Colorectal carcinoma is the most common malignancy of the gastrointestinal tract. Over 140,000 new cases are diagnosed annually in the United States, and more than 50,000 patients die of this disease each year, making colorectal cancer the third most lethal cancer in the United States.51
The incidence is similar in men and women and has remained fairly constant over the past 20 years; however, the widespread adoption of current national screening programs is gradually decreasing the incidence of this common and lethal disease. Early detection and improvements in medical and surgical care are thought to be responsible for the decreasing mortality of colorectal cancer observed in recent years.
Epidemiology (Risk Factors)
Identification of risk factors for development of colorectal cancer is essential to establish screening and surveillance programs in appropriately targeted populations.
Aging is the dominant risk factor for colorectal cancer, with incidence rising steadily after age 50 years. More than 90% of cases diagnosed are in people older than age 50 years. This is the rationale for initiating screening tests of asymptomatic patients at average risk of developing colorectal cancer at age 50 years. However, individuals of any age can develop colorectal cancer, so symptoms such as a significant change in bowel habits, rectal bleeding, melena, unexplained anemia, or weight loss require a thorough evaluation.
Approximately 80% of colorectal cancers occur sporadically, while 20% arise in patients with a known family history of colorectal cancer. Advances in the understanding of these familial disorders have led to interest in early diagnosis using genetic testing. Because of the medical, legal, and ethical considerations that are involved in this type of testing, all patients should be offered genetic counseling if a familial syndrome is suspected.
Environmental and Dietary Factors
The observation that colorectal carcinoma occurs more commonly in populations that consume diets high in animal fat and low in fiber has led to the hypothesis that dietary factors contribute to carcinogenesis. A diet high in saturated or polyunsaturated fats increases risk of colorectal cancer, while a diet high in oleic acid (olive oil, coconut oil, fish oil) does not increase risk. Animal studies suggest that fats may be directly toxic to the colonic mucosa and thus may induce early malignant changes. In contrast, a diet high in vegetable fiber appears to be protective. A correlation between alcohol intake and incidence of colorectal carcinoma has also been suggested. Ingestion of calcium, selenium, vitamins A, C, and E, carotenoids, and plant phenols may decrease the risk of developing colorectal cancer. Obesity and sedentary lifestyle dramatically increase cancer-related mortality in a number of malignancies, including colorectal carcinoma. This knowledge is the basis for primary prevention strategies to eliminate colorectal cancer by altering diet and lifestyle.52
Inflammatory Bowel Disease
Patients with long-standing colitis from inflammatory bowel disease are at increased risk for the development of colorectal cancer. It is hypothesized that chronic inflammation predisposes the mucosa to malignant changes, and there is some evidence that degree of inflammation influences risk. In general, the duration and extent of colitis correlate with risk. Other factors thought to increase risk include the presence of primary sclerosing cholangitis and family history of colorectal cancer.
Cigarette smoking is associated with an increased risk of colonic adenomas, especially after more than 35 years of use. Patients with ureterosigmoidostomy are also at increased risk for both adenoma and carcinoma formation.53
Acromegaly, which is associated with increased levels of circulating human growth hormone and insulin-like growth factor-1, increases risk as well. Pelvic irradiation may increase the risk of developing rectal carcinoma. However, it is unclear whether this represents a direct effect of radiation damage or is instead a correlation between the development of rectal cancer and a history of another pelvic malignancy; for example among patients who develop prostate cancer and are treated with radiation, the risk of rectal cancer increases significantly.54
Pathogenesis of Colorectal Cancer
Over the past two decades, an intense research effort has focused on elucidating the genetic defects and molecular abnormalities associated with the development and progression of colorectal adenomas and carcinoma. Mutations may cause activation of oncogenes (K-ras) and/or inactivation of tumor suppressor genes (APC, deleted in colorectal carcinoma [DCC], p53). Colorectal carcinoma is thought to develop from adenomatous polyps by accumulation of these mutations in what has come to be known as the adenoma-carcinoma sequence (Fig. 29-22).
Schematic showing progression from normal colonic epithelium to carcinoma of the colon.
Defects in the APC gene were first described in patients with FAP. By investigating these families, characteristic mutations in the APC gene were identified. They are now known to be present in 80% of sporadic colorectal cancers as well.
The APC gene is a tumor suppressor gene. Mutations in both alleles are necessary to initiate polyp formation. The majority of mutations are premature stop codons, which result in a truncated APC protein. In FAP, the site of mutation correlates with the clinical severity of the disease. For example, mutations in either the 3′ or 5′ end of the gene result in attenuated forms of FAP (AFAP), whereas mutations in the center of the gene result in more virulent disease. Thus, knowledge of the specific mutation in a family may help guide clinical decision making.
APC inactivation alone does not result in a carcinoma. Instead, this mutation sets the stage for the accumulation of genetic damage that results in malignancy. Additional mutations may include activation or inactivation of a variety of genes.
One of the most commonly involved genes in colorectal cancer is K-ras. K-ras, a signaling molecule in the epidermal growth factor receptor (EGFR) pathway, is classified as a proto-oncogene because mutation of only one allele will perturb the cell cycle. The K-ras gene product is a G-protein involved in intracellular signal transduction. When active, K-ras binds guanosine triphosphate (GTP); hydrolysis of GTP to guanosine diphosphate (GDP) then inactivates the G-protein. Mutation of K-ras results in an inability to hydrolyze GTP, thus leaving the G-protein permanently in the active form. It is thought that this then leads to uncontrolled cell division. Other EGFR signaling molecules such as BRAF have also been implicated in colorectal cancer pathogenesis and progression, and ongoing research is focusing on elucidating their roles in this disease.
Another common mutation occurs in the MYH gene on chromosome 1p.55,56 MYH is a base excision repair gene, and biallelic deletion results in changes in other downstream molecules. Since its discovery, MYH mutations have been associated with an AFAP phenotype in addition to sporadic cancers.55 Unlike APC gene mutations that are expressed in an autosomal dominant pattern, the requirement for biallelic mutation in MYH results in an autosomal recessive pattern of inheritance.
The tumor suppressor gene p53 has been well characterized in a number of malignancies. The p53 protein appears to be crucial for initiating apoptosis in cells with irreparable genetic damage. Mutations in p53 are present in 75% of colorectal cancers.
Deletion of the tumor suppressor phosphatase and tensin homolog (PTEN) appears to be involved in a number of hamartomatous polyposis syndromes. Deletions in PTEN have been identified in juvenile polyposis, Peutz-Jeghers syndrome, Cowden’s syndrome, and PTEN hamartoma syndrome, in addition to multiple endocrine neoplasia type IIB.12
The mutations involved in colorectal cancer pathogenesis and progression are now recognized to accumulate via one of three major genetic pathways: the loss of heterozygosity (LOH; chromosomal instability) pathway, the microsatellite instability (MSI) pathway, and the CpG island methylation (CIMP; serrated methylated) pathway.
The Loss of Heterozygosity Pathway
The LOH pathway is characterized by chromosomal deletions and tumor aneuploidy. Eighty percent of colorectal carcinomas appear to arise from mutations in the LOH pathway. This pathway was first described in patients with FAP in whom mutations of the APC gene were found to be inherited.
Another example of LOH occurs in the region of chromosome 18q. This region has been found to be deleted in up to 70% of colorectal cancers. Two tumor suppressor genes, DCC and SMAD4, are located in this region, and as such, deletion of 18q may result in the loss of one or both of these genes. DCC is a tumor suppressor gene, and loss of both alleles is required for malignant degeneration. The main role of this molecule appears to be in the central nervous system, where it is involved in neural differentiation and axonal migration. This observation has led to the hypothesis that DCC may be involved in differentiation and cellular adhesion in colorectal cancer, but this theory remains unproven.57 DCC mutations are present in more than 70% of colorectal carcinomas and may negatively impact prognosis. SMAD4 functions in the signaling cascade of transforming growth factor beta and beta-catenin (also a downstream effector of the APC gene). Loss of either of these genes is thought to promote cancer progression.
The Microsatellite Instability Pathway
Many of the remaining colorectal carcinomas are thought to arise from mutations in the MSI pathway, which is characterized by errors in mismatch repair during DNA replication. These errors in mismatch repair were first described in HNPCC (Lynch’s syndrome), but are now recognized to be present in many sporadic tumors as well. A number of genes have been identified that appear to be crucial for recognizing and repairing DNA replication errors. These mismatch repair genes include MSH2, MLH1, PMS1, PMS2, and MSH6/GTBP. A mutation in one of these genes predisposes a cell to mutations, which may occur in proto-oncogenes or tumor suppressor genes. Accumulation of these errors then leads to genomic instability and ultimately to carcinogenesis.
Microsatellites are regions of the genome in which short base-pair segments are repeated several times, regions that are particularly prone to replication error. Consequently, a mutation in a mismatch repair gene produces variable lengths of these repetitive sequences, a finding that has been described as MSI.
Tumors associated with MSI appear to have different biologic characteristics than do tumors that result from the LOH pathway. Tumors with MSI are more likely to be in the right colon and possess diploid DNA and are associated with a better prognosis than tumors that arise from the LOH pathway that are microsatellite stable. Tumors arising from the LOH pathway tend to occur in the more distal colon, often have chromosomal aneuploidy, and are associated with a poorer prognosis.
CpG Island Methylation Pathway
In the recently described CIMP pathway, genes do not accumulate mutations (deletions or insertions of bases), but instead are activated or inactivated by methylation. This process has been called epigenetic alteration to differentiate it from the more traditional genetic alterations or true mutations. In normal cells, methylation is critical for regulation of gene expression. In cancer, aberrant methylation (either hyper- or hypomethylation), usually of a promoter region, results in abnormal activation or inactivation of genes. This gene silencing or, alternatively, activation results in a phenotype similar to that present with a true gene mutation. This pathway has also been called the serrated methylated pathway because of the observation that serrated polyps often harbor aberrant methylation in contrast to adenomatous polyps that are more often associated with mutations in the APC gene (LOH pathway).58
Although these classifications are useful for understanding the mechanisms underlying carcinogenesis, they are not mutually exclusive. For example, a mismatch repair gene may be inactivated by methylation. Errors in mismatch repair may then allow mutations to inactivate a tumor suppressor gene. In addition, there is considerable interest in targeting molecules in each of these pathways in order to design better anticancer agents. Finally, ongoing research is focusing on the utility of molecular profiling in predicting prognosis and/or response to treatment.
It is now well accepted that the majority of colorectal carcinomas evolve from adenomatous polyps; this sequence of events is the adenoma-carcinoma sequence. Polyp is a nonspecific clinical term that describes any projection from the surface of the intestinal mucosa regardless of its histologic nature. Colorectal polyps may be classified as neoplastic (tubular adenoma, villous adenoma, tubulovillous adenomas, serrated adenomas/polyps), hyperplastic, hamartomatous (juvenile, Peutz-Jeghers, Cronkite-Canada), or inflammatory (pseudopolyp, benign lymphoid polyp).
Adenomatous polyps are common, occurring in up to 25% of the population older than 50 years of age in the United States. By definition, these lesions are dysplastic. The risk of malignant degeneration is related to both the size and type of polyp. Tubular adenomas are associated with malignancy in only 5% of cases, whereas villous adenomas may harbor cancer in up to 40%. Tubulovillous adenomas are at intermediate risk (22%). Invasive carcinomas are rare in polyps smaller than 1 cm; the incidence increases with size. The risk of carcinoma in a polyp larger than 2 cm is 35% to 50%. Although most neoplastic polyps do not evolve to cancer, most colorectal cancers originate as a polyp. It is this fact that forms the basis for secondary prevention strategies to eliminate colorectal cancer by targeting the neoplastic polyp for removal before malignancy develops.
Polyps may be pedunculated or sessile. Most pedunculated polyps are amenable to colonoscopic snare excision. Removal of sessile polyps is often more challenging. Special colonoscopic techniques, including saline lift, piecemeal snare excision, and endoscopic mucosal resection facilitate successful removal of many sessile polyps. For rectal sessile polyps, transanal operative excision is preferred because it produces an intact, single pathology specimen that can be used to determine the need for further therapy. Interpretation of the precise depth of invasion of a cancer arising in a sessile polyp after piecemeal excision is often impossible. The site of sessile polypectomies should be marked by injection of India ink to guide follow-up colonoscopy sessions to ensure that the polyp has been completely removed and to facilitate identification of the involved bowel segment should operative resection be necessary. Colectomy is reserved for cases in which colonoscopic removal is impossible, such as large, flat lesions, or if a focus of invasive cancer is confirmed in the specimen.
Complications of polypectomy include perforation and bleeding. A small perforation (microperforation) in a fully prepared, stable patient may be managed with bowel rest, broad-spectrum antibiotics, and close observation. Signs of sepsis, peritonitis, or deterioration in clinical condition are indications for laparotomy. Bleeding may occur immediately after polypectomy or may be delayed. The bleeding will usually stop spontaneously, but colonoscopy may be required to resnare a bleeding stalk or cauterize the lesion. Occasionally angiography and infusion of vasopressin may be necessary. Rarely, colectomy is required.
Hyperplastic polyps are extremely common in the colon. These polyps are usually small (<5 mm) and show histologic characteristics of hyperplasia without any dysplasia. They are not considered premalignant, but cannot be distinguished from adenomatous polyps colonoscopically and are therefore often removed. In contrast, large hyperplastic polyps (>2 cm) may have a slight risk of malignant degeneration. Moreover, large polyps may harbor foci of adenomatous tissue and dysplasia. Hyperplastic polyposis is a rare disorder in which multiple large hyperplastic polyps occur in young adults. These patients are at slightly increased risk for the development of colorectal cancer.
Serrated polyps are a recently recognized, histologically distinct group of neoplastic polyps. These lesions were long thought to be similar to hyperplastic polyps with minimal malignant potential. However, it has become clear that some of these polyps will develop into invasive cancers. In addition, a familial serrated polyposis syndrome has recently been described. Serrated polyps should be treated like adenomatous polyps.59
Hamartomatous Polyps (Juvenile Polyps)
In contrast to adenomatous and serrated polyps, hamartomatous polyps (juvenile polyps) usually are not premalignant. These lesions are the characteristic polyps of childhood but may occur at any age. Bleeding is a common symptom, and intussusception and/or obstruction may occur. Because the gross appearance of these polyps is identical to adenomatous polyps, these lesions should also be treated by polypectomy. In contrast to adenomatous polyposis syndromes, these conditions are often associated with mutation in PTEN.
Familial juvenile polyposis is an autosomal dominant disorder in which patients develop hundreds of polyps in the colon and rectum. Unlike solitary juvenile polyps, these lesions may degenerate into adenomas and eventually carcinoma. Annual screening should begin between the ages of 10 and 12 years. Treatment is surgical and depends in part on the degree of rectal involvement. If the rectum is relatively spared, a total abdominal colectomy with ileorectal anastomosis may be performed with subsequent close surveillance of the retained rectum. If the rectum is carpeted with polyps, total proctocolectomy is the more appropriate operation. These patients are candidates for ileal pouch–anal reconstruction to avoid a permanent stoma.
Peutz-Jeghers syndrome is characterized by polyposis of the small intestine and, to a lesser extent, polyposis of the colon and rectum. Characteristic melanin spots are often noted on the buccal mucosa and lips of these patients. The polyps of Peutz-Jeghers syndrome are generally considered to be hamartomas and are not thought to be at significant risk for malignant degeneration. However, carcinoma may occasionally develop. Because the entire length of the gastrointestinal tract may be affected, surgery is reserved for symptoms such as obstruction or bleeding or for patients in whom polyps develop adenomatous features. Screening consists of a baseline colonoscopy and upper endoscopy at age 20 years, followed by annual flexible sigmoidoscopy thereafter.
Cronkite-Canada syndrome is a disorder in which patients develop gastrointestinal polyposis in association with alopecia, cutaneous pigmentation, and atrophy of the fingernails and toenails. Diarrhea is a prominent symptom, and vomiting, malabsorption, and protein-losing enteropathy may occur. Most patients die of this disease despite maximal medical therapy, and surgery is reserved for complications of polyposis such as obstruction.
Cowden’s syndrome is an autosomal dominant disorder with hamartomas of all three embryonal cell layers. Facial trichilemmomas, breast cancer, thyroid disease, and gastrointestinal polyps are typical of the syndrome. Patients should be screened for cancers. Treatment is otherwise based on symptoms.
Inflammatory Polyps (Pseudopolyps)
Inflammatory polyps occur most commonly in the context of inflammatory bowel disease, but may also occur after amebic colitis, ischemic colitis, and schistosomal colitis. These lesions are not premalignant, but they cannot be distinguished from adenomatous polyps based on gross appearance and therefore should be removed. Microscopic examination shows islands of normal, regenerating mucosa (the polyp) surrounded by areas of mucosal loss. Polyposis may be extensive, especially in patients with severe colitis, and may mimic FAP.
Inherited Colorectal Carcinoma
Many of the genetic defects originally described in hereditary cancers have subsequently been found in sporadic tumors. Although the majority of colorectal cancer is sporadic, several hereditary syndromes provide paradigms for the study of this disease. Insight gained from studying inherited colorectal cancer syndromes has led to better understanding of the genetics of colorectal carcinoma.
Familial Adenomatous Polyposis
This rare autosomal dominant condition accounts for only about 1% of all colorectal adenocarcinomas. Nevertheless, this syndrome has provided tremendous insight into the molecular mechanisms underlying colorectal carcinogenesis. The genetic abnormality in FAP is a mutation in the APC gene, located on chromosome 5q. Of patients with FAP, APC mutation testing is positive in 75% of cases. While most patients with FAP will have a known family history of the disease, up to 25% present without other affected family members. Clinically, patients develop hundreds to thousands of adenomatous polyps shortly after puberty. The lifetime risk of colorectal cancer in FAP patients approaches 100% by age 50 years.
Flexible sigmoidoscopy of first-degree relatives of FAP patients beginning at age 10 to 15 years has been the traditional mainstay of screening. Today, following genetic counseling, APC gene testing may be used to screen family members, providing an APC mutation has been identified. If APC testing is positive in a relative of a patient with a known APC mutation, annual flexible sigmoidoscopy beginning at age 10 to 15 years is done until polyps are identified. If APC testing is negative, the relative can be screened starting at age 50 years per average-risk guidelines. If APC testing is refused or unavailable, or if a mutation cannot be identified, annual flexible sigmoidoscopy beginning at age 10 to 15 years is performed until age 24 years. Screening flexible sigmoidoscopy is then done every 2 years until age 34 years, every 3 years until age 44 years, and then every 3 to 5 years.
FAP patients are also at risk for the development of adenomas anywhere in the gastrointestinal tract, particularly in the duodenum. Periampullary carcinoma is a particular concern. Upper endoscopy is therefore recommended for surveillance every 1 to 3 years beginning at age 25 to 30 years.
Once the diagnosis of FAP has been made and polyps are developing, treatment is surgical. Four factors affect the choice of operation: age of the patient; presence and severity of symptoms; extent of rectal polyposis; and presence and location of cancer or desmoid tumors. Three operative procedures can be considered: total proctocolectomy with an end (Brooke) ileostomy; total abdominal colectomy with ileorectal anastomosis; and restorative proctocolectomy with ileal pouch–anal anastomosis with or without a temporary ileostomy. Most patients elect to have an ileal pouch–anal anastomosis in the absence of a distal rectal cancer, a mesenteric desmoid tumor that prevents the ileum from reaching the anus, or poor sphincter function. Mucosectomy has been advocated in patients with FAP undergoing ileal pouch–anal anastomosis because of the risk of neoplasia in the anal transition zone, but the requirement for this procedure remains controversial. Although patient satisfaction with this procedure remains high, function may not be ideal, and up to 50% of patients experience some degree of incontinence. Total abdominal colectomy with an ileorectal anastomosis is also an option in these patients, but requires vigilant surveillance of the retained rectum for development of rectal cancer. There is increasing data suggesting that the administration of cyclooxygenase-2 (COX-2) inhibitors (celecoxib, sulindac) may slow or prevent the development of polyps.60
FAP may be associated with extraintestinal manifestations such as congenital hypertrophy of the retinal pigmented epithelium, desmoid tumors, epidermoid cysts, mandibular osteomas (Gardner’s syndrome), and central nervous system tumors (Turcot’s syndrome). Desmoid tumors in particular, can make surgical management difficult and are a source of major morbidity and mortality in these patients. Desmoid tumors are often hormone responsive, and growth may be inhibited in some patients with tamoxifen. COX-2 inhibitors and nonsteroidal, anti-inflammatory drugs may also be beneficial in this setting.
Attenuated Familial Adenomatous Polyposis
AFAP is a recognized variant of FAP. Patients present later in life with fewer polyps (usually 10–100) predominantly located in the right colon, when compared to classic FAP. Colorectal carcinoma develops in more than 50% of these patients, but occurs later (average age, 55 years). Patients are also at risk for duodenal polyposis. However, in contrast to FAP, APC gene mutations are present in only about 30% of patients with AFAP. When present, these mutations are expressed in an autosomal dominant pattern.
Mutations in MYH also result in the AFAP phenotype but are expressed in an autosomal recessive pattern. It has been suggested that MYH mutations may be responsible for AFAP in patients who do not have a detectable APC gene mutation.61
Genetic testing is often offered to patients with suspected AFAP. When positive, genetic counseling and testing may be used to screen at-risk family members. If the family mutation is unknown, screening colonoscopy is recommended beginning at age 13 to 15 years, then every 4 years to age 28 years, and then every 3 years. These patients are often candidates for a total abdominal colectomy with ileorectal anastomosis because the limited polyposis in the rectum can usually be treated by colonoscopic snare excision.62,63 Prophylaxis with COX-2 inhibitors also may be appropriate. Because of the more subtle phenotype in these patients, it is important to rule out other familial syndromes such as HNPCC (Lynch’s syndrome) and the more common familial colorectal cancer.
Hereditary Nonpolyposis Colon Cancer (Lynch’s Syndrome)
HNPCC (Lynch’s syndrome) is more common than FAP, but is still extremely rare (1%–3% of all colon cancers). The genetic defects associated with HNPCC arise from errors in mismatch repair, the phenotypic result being MSI. HNPCC is inherited in an autosomal dominant pattern and is characterized by the development of colorectal carcinoma at an early age (average age, 40–45 years). Approximately 70% of affected individuals will develop colorectal cancer. Cancers appear in the proximal colon more often than in sporadic colorectal cancer and have a better prognosis regardless of stage. The risk of synchronous or metachronous colorectal carcinoma is 40%. HNPCC may also be associated with extracolonic malignancies, including endometrial carcinoma, which is most common, and ovarian, pancreas, stomach, small bowel, biliary, and urinary tract carcinomas. The diagnosis of HNPCC is made based on family history. The Amsterdam criteria for clinical diagnosis of HNPCC are three affected relatives with histologically verified adenocarcinoma of the large bowel (one must be a first-degree relative of one of the others) in two successive generations of a family with one patient diagnosed before age 50 years. The presence of other HNPCC-related carcinomas should raise the suspicion of this syndrome. In a patient with an established diagnosis of colorectal cancer, tumor testing for presence of mismatch repair gene products (immunohistochemistry) and/or MSI can sometimes serve as screening for this syndrome.64,65
HNPCC results from mutations in mismatch repair genes, and like FAP, specific mutations are associated with different phenotypes. For example, mutations in PMS2 or MSH6 result in a more attenuated form of HNPCC when compared to mutations in other genes. MSH6 inactivation also appears to be associated with a higher risk for endometrial cancer. Further significance of these specific mutations remains to be determined.
Screening colonoscopy is recommended annually for at-risk patients beginning at either age 20 to 25 years or 10 years younger than the youngest age at diagnosis in the family, whichever comes first.66 Because of the high risk of endometrial carcinoma, transvaginal ultrasound or endometrial aspiration biopsy is also recommended annually after age 25 to 35 years. Because there is a 40% risk of developing a second colon cancer, total colectomy with ileorectal anastomosis is recommended once adenomas or a colon carcinoma is diagnosed. Annual proctoscopy is necessary because the risk of developing rectal cancer remains high. Similarly, prophylactic hysterectomy and bilateral salpingo-oophorectomy should be considered in women who have completed childbearing.
Familial Colorectal Cancer
Nonsyndromic familial colorectal cancer accounts for 10% to 15% of patients with colorectal cancer. The lifetime risk of developing colorectal cancer increases with a family history of the disease. The lifetime risk of colorectal cancer in a patient with no family history of this disease (average-risk population) is approximately 6%, but rises to 12% if one first-degree relative is affected and to 35% if two first-degree relatives are affected. Age of onset also impacts risk, and a diagnosis before the age of 50 years is associated with a higher incidence in family members. Screening colonoscopy is recommended every 5 years beginning at age 40 years or beginning 10 years before the age of the earliest diagnosed patient in the pedigree. While there are no specific genetic abnormalities that are associated with familial colorectal cancer, any of the defects found in either the LOH pathway or MSI pathway may be present in these patients.
Prevention: Screening and Surveillance
Because the majority of colorectal cancers are thought to arise from adenomatous polyps, preventive measures focus on identification and removal of these premalignant lesions. In addition, many cancers are asymptomatic, and screening may detect these tumors at an early and curable stage (Table 29-1). Although screening for colorectal cancer decreases the incidence of cancer and cancer-related mortality, the optimal method of screening remains controversial. Screening guidelines are meant for asymptomatic patients.61,66,67,68 Any patient with a gastrointestinal complaint (bleeding, change in bowel habits, pain, etc.) requires a complete evaluation, usually by colonoscopy.
Table 29-1Advantages and disadvantages of screening modalities for asymptomatic individuals ||Download (.pdf) Table 29-1 Advantages and disadvantages of screening modalities for asymptomatic individuals
| ||ADVANTAGES ||DISADVANTAGES |
Fecal occult blood testing
Ease of use and noninvasive
Good sensitivity with repeat testing
May not detect most polyps
Colonoscopy required for positive result
Poor compliance with serial testing
|Sigmoidoscopy || |
Examines colon most at risk
Very sensitive for polyp detection in left colon
Does not require full bowel preparation (enemas only)
Slight risk of perforation or bleeding
May miss proximal lesions
Colonoscopy required if polyp identified
|Colonoscopy || |
Examines entire colon
Highly sensitive and specific
Uncomfortable and requires sedation
Requires bowel preparation
Risk of perforation or bleeding
Double-contrast barium enema
Examines entire colon
Good sensitivity for polyps >1 cm
Examines entire colon
Requires bowel preparation
Less sensitivity for polyps <1 cm
May miss lesions in the sigmoid colon
Colonoscopy required for positive result
|Computed tomography colonography (virtual colonoscopy) || |
Sensitivity may be as good as colonoscopy
Requires bowel preparation
Insensitive for small polyps
Minimal experience and data
Colonoscopy required for positive result
Fecal Occult Blood Testing
FOBT is known to reduce colorectal cancer mortality by 33% and metastatic disease by 50%. However, FOBT is relatively insensitive, missing up to 50% of cancers and the majority of adenomas. Its specificity is low because 90% of patients with positive tests do not have colorectal cancer. Compliance with annual testing is low and costs are significant if one includes the colonoscopy examinations done to evaluate patients with positive FOBT. Nonetheless, the direct evidence that FOBT screening is efficacious and decreases both the incidence and mortality of colorectal cancer is so strong that national guidelines recommend annual FOBT screening for asymptomatic, average-risk Americans older than 50 years of age as one of several accepted strategies. Newer immunohistochemical methods for detecting human globin may prove to be more sensitive and specific.69 A positive FOBT test should be followed by colonoscopy.
Screening by flexible sigmoidoscopy every 5 years may lead to a 60% to 70% reduction in mortality from colorectal cancer, chiefly by identifying high-risk individuals with adenomas. However, it is important to recognize that lesions in the proximal colon cannot be identified, and for this reason, flexible sigmoidoscopy has often been paired with air-contrast barium enema to detect transverse and right colon lesions. Patients found to have a polyp, cancer, or other lesion on flexible sigmoidoscopy will require colonoscopy.70
Fecal Occult Blood Testing and Flexible Sigmoidoscopy
Several trials have shown that FOBT screening is least effective at detecting rectosigmoid cancers.69,71 This is precisely the area screened by flexible sigmoidoscopy; thus, the combination of the two tests has been suggested as a reasonable screening strategy. Winawer and colleagues, in a study of 12,479 subjects, showed that the combination of FOBT annually with flexible sigmoidoscopy every 5 years resulted in lower mortality from colorectal cancer and better survival in patients with colorectal cancer.72 Such data led to the American Cancer Society recommendations that one of the acceptable screening regimens for average-risk Americans is the combination of FOBT annually and flexible sigmoidoscopy every 5 years; this combination was preferred over either test alone. The addition of air-contrast barium enema to assess the proximal colon may improve sensitivity as well.
Colonoscopy is currently the most accurate and most complete method for examining the large bowel. This procedure is highly sensitive for detecting even small polyps (<1 cm) and allows biopsy, polypectomy, control of hemorrhage, and dilation of strictures. However, colonoscopy does require mechanical bowel preparation, and the discomfort associated with the procedure requires conscious sedation in most patients. Colonoscopy is also considerably more expensive than other screening modalities and requires a well-trained endoscopist. The risk of a major complication after colonoscopy (perforation and hemorrhage) is extremely low (0.2%–0.3%). Nevertheless, deaths have been reported.
Air-Contrast Barium Enema
Air-contrast barium enema is also highly sensitive for detecting polyps greater than 1 cm in diameter (90% sensitivity). Unfortunately, there are no studies proving its efficacy for screening large populations. Accuracy is greatest in the proximal colon but may be compromised in the sigmoid colon if there is significant diverticulosis. The major disadvantages of barium enema are the need for mechanical bowel preparation and the requirement for colonoscopy if a lesion is discovered.
Computed Tomography Colonography (Virtual Colonoscopy)
Advances in imaging technology have created a number of less invasive, but highly accurate tools for screening. CT colonography makes use of helical CT technology and three-dimensional reconstruction to image the intraluminal colon. A present, patients require a mechanical bowel preparation. The colon is then insufflated with air, a spiral CT is performed, and both two-dimensional and three-dimensional images are generated. In the hands of a qualified radiologist, sensitivity appears to be as good as colonoscopy for colorectal cancers and polyps greater than 1 cm in size.73 Colonoscopy is required if a lesion is identified. CT colonography is also useful for imaging the proximal colon in cases of obstruction or if a colonoscopy cannot be completed. Limitations of this technique include false-positive results from retained stool, diverticular disease, haustral folds, motion artifacts, and an inability to detect flat adenomas.
Current American Cancer Society guidelines advocate screening for the average-risk population (asymptomatic, no family history of colorectal carcinoma, no personal history of polyps or colorectal carcinoma, no familial syndrome) beginning at age 50 years. Recommended procedures include yearly FOBT, flexible sigmoidoscopy every 5 years, FOBT and flexible sigmoidoscopy in combination, air-contrast barium enema every 5 years, or colonoscopy every 10 years.66 Patients with other risk factors should be screened earlier and more frequently (Table 29-2).
Table 29-2Screening guidelines for colorectal cancer ||Download (.pdf) Table 29-2 Screening guidelines for colorectal cancer
|POPULATION ||INITIAL AGE ||RECOMMENDED SCREENING TEST |
|Average risk ||50 y || |
Annual FOBT or
Flexible sigmoidoscopy every 5 y or
Annual FOBT and flexible sigmoidoscopy every 5 y or
Air-contrast barium enema every 5 y or
Colonoscopy every 10 y
Colonoscopy at first detection; then colonoscopy in 3 y
If no further polyps, colonoscopy every 5 y
If polyps, colonoscopy every 3 y
Annual colonoscopy for >5 adenomas
Pretreatment colonoscopy; then at 12 mo after curative resection; then colonoscopy after 3 y; then colonoscopy every 5 y, if no new lesions
Ulcerative colitis, Crohn’s colitis
At diagnosis; then after 8 y for pancolitis, after 15 y for left-sided colitis
Colonoscopy with multiple biopsies every 1–2 y
|FAP ||10–12 y || |
Annual flexible sigmoidoscopy
Upper endoscopy every 1–3 y after polyps appear
|Attenuated FAP ||20 y || |
Annual flexible sigmoidoscopy
Upper endoscopy every 1–3 y after polyps appear
|HNPCC ||20–25 y || |
Colonoscopy every 1–2 y
Endometrial aspiration biopsy every 1–2 y
|Familial colorectal cancer first-degree relative ||40 y or 10 y before the age of the youngest affected relative || |
Colonoscopy every 5 y
Increase frequency if multiple family members are affected, especially before 50 y
Routes of Spread and Natural History
Carcinoma of the colon and rectum arises in the mucosa. The tumor subsequently invades the bowel wall and eventually adjacent tissues and other viscera. Tumors may become bulky and circumferential, leading to colon obstruction. Local extension (especially in the rectum) may occasionally cause obstruction of other organs such as the ureter.
Regional lymph node involvement is the most common form of spread of colorectal carcinoma and usually precedes distant metastasis or the development of carcinomatosis. The likelihood of nodal metastasis increases with tumor size, poorly differentiated histology, lymphovascular invasion, and depth of invasion. The T stage (depth of invasion) is the single most significant predictor of lymph node spread. Carcinoma in situ (Tis) in which there is no penetration of the muscularis mucosa (basement membrane) has also been called high-grade dysplasia and should carry no risk of lymph node metastasis. Small lesions confined to the bowel wall (T1 and T2) are associated with lymph node metastasis in 5% to 20% of cases, whereas larger tumors that invade through the bowel wall or into adjacent organs (T3 and T4) are likely to have lymph node metastasis in more than 50% of cases. The number of lymph nodes with metastases correlates with the presence of distant disease and inversely with survival. Four or more involved lymph nodes predict a poor prognosis. In colon cancer, lymphatic spread usually follows the major venous outflow from the involved segment of the colon. Lymphatic spread from the rectum follows two routes. In the upper rectum, drainage ascends along the superior rectal vessels to the inferior mesenteric nodes. In the lower rectum, lymphatic drainage may course along the middle rectal vessels. Nodal spread along the inferior rectal vessels to the internal iliac nodes or groin is rare unless the tumor involves the anal canal or the proximal lymphatics are blocked with tumor (Fig. 29-23).
Lymphatic drainage of the rectum. a. = artery.
The most common site of distant metastasis from colorectal cancer is the liver. These metastases arise from hematogenous spread via the portal venous system. Like lymph node metastasis, the risk of hepatic metastasis increases with tumor size and tumor grade. However, even small tumors may produce distant metastasis. The lung is also a site of hematogenous spread, but this rarely occurs in isolation. Carcinomatosis (diffuse peritoneal metastases) occurs by peritoneal seeding and has a dismal prognosis.
Staging and Preoperative Evaluation
Symptoms of colon and rectal cancers are nonspecific and generally develop when the cancer is locally advanced. The classic first symptoms are a change in bowel habits and rectal bleeding. Abdominal pain, bloating, and other signs of obstruction typically occur with larger tumors and suggest more advanced disease. Because of the caliber of the bowel and the consistency of the stool, left-sided tumors are more likely to cause obstruction than are right-sided tumors. Rectal tumors may cause bleeding, tenesmus, and pain. Alternatively, patients may be asymptomatic and/or present with unexplained anemia, weight loss, or poor appetite.
Colorectal cancer staging is based on tumor depth and the presence or absence of nodal or distant metastases. Older staging systems, such as the Dukes’ Classification and its Astler-Coller modification, have been replaced by the tumor-node-metastasis (TNM) staging system (Table 29-3).74 Stage I disease includes adenocarcinomas that are invasive through the muscularis mucosa but are confined to the submucosa (T1) or the muscularis propria (T2) in the absence of nodal metastases. Stage II disease consists of tumors that invade through the bowel wall into the subserosa or nonperitonealized pericolic or perirectal tissues (T3) or into other organs or tissues or through the visceral peritoneum (T4) without nodal metastases. Stage III disease includes any T stage with nodal metastases, and stage IV disease denotes distant metastases.
Table 29-3TNM staging of colorectal carcinoma ||Download (.pdf) Table 29-3 TNM staging of colorectal carcinoma
| ||DEFINITION |
|Tumor stage (T) |
|TX ||Cannot be assessed |
|T0 ||No evidence of cancer |
|Tis ||Carcinoma in situ |
|T1 ||Tumor invades submucosa |
|T2 ||Tumor invades muscularis propria |
|T3 ||Tumor invades through muscularis propria into subserosa or into nonperitonealized pericolic or perirectal tissues |
|T4 ||Tumor directly invades other organs or tissues or perforates the visceral peritoneum of specimen |
|Nodal stage (N) |
|NX ||Regional lymph nodes cannot be assessed |
|N0 ||No lymph node metastasis |
|N1 ||Metastasis to one to three pericolic or perirectal lymph nodes |
|N2 ||Metastasis to four or more pericolic or perirectal lymph nodes |
|N3 ||Metastasis to any lymph node along a major named vascular trunk |
|Distant metastasis (M) |
|MX ||Presence of distant metastasis cannot be assessed |
|M0 ||No distant metastasis |
|M1 ||Distant metastasis present |
The preoperative evaluation usually identifies stage IV disease. In colon cancer, differentiating stages I, II, and III depends on examination of the resected specimen. In rectal cancer, endorectal ultrasound or MRI may predict the stage (ultrasound stage, uTxNx) preoperatively, but the final determination depends on pathologic examination of the resected tumor and adjacent lymph nodes (pathologic stage, pTxNx). Disease stage correlates with 5-year survival. Patients with stages I and II disease can expect excellent survival rates. The presence of nodal metastases (stage III) decreases survival (Table 29-4). The 5-year survival rate with stage IV disease is less than 16%. However, in well-selected patients, metastasectomy, especially of isolated liver or lung lesions, can result in cure. In rectal cancer, staging has been further refined, and outcomes suggest that subgroups of patients within each stage may have very different prognoses (Table 29-5). If the mesorectum around a rectal cancer is involved or threatened (only 1–2 mm of clearance), there is a very high likelihood of local recurrence and a poor prognosis. This circumferential or radial margin is probably best assessed preoperatively by MRI. Although nodal involvement is the single most important prognostic factor in colorectal carcinoma, tumor characteristics, such as degree of differentiation, mucinous or signet-ring cell histology, vascular invasion, and DNA aneuploidy, also adversely affect prognosis. Molecular profiling is currently being studied in an effort to further improve prognostic indicators.
Table 29-4TNM staging of colorectal carcinoma and 5-year survival ||Download (.pdf) Table 29-4 TNM staging of colorectal carcinoma and 5-year survival
|STAGE ||TNM ||5-Y SURVIVAL (%) |
|I ||T1–2, N0 ||93.2 |
|IIa ||T3, N0 ||84.7 |
|IIb ||T4, N0 ||72.2 |
|IIIa ||T1–2, N1 ||83.4 |
|IIIb ||T3, N1 ||64.1 |
|IIIc ||T3, N2 or T4, N1–2 ||44.3 |
|IV ||Tany, Nany, M1 ||8.1 |
Table 29-5American Joint Committee on Cancer staging ||Download (.pdf) Table 29-5 American Joint Committee on Cancer staging
|TNM ||STAGE ||LOCAL RECURRENCE (%) ||SURVIVAL (%) |
|T1–2 N0 ||I ||<5 ||90 |
|T3 N0 ||IIA ||8 ||74 |
|T4 N0 ||IIB ||15 ||65 |
|T1–2 N1 ||IIIA ||6 ||81 |
|T1–2 N2 ||IIIB ||8 ||69 |
|T3 N1 ||IIIB ||11 ||61 |
|T3 N2 ||IIIC ||15 ||48 |
|T4 N1–2 ||IIIC ||19–22 ||36 |
|TNM = tumor-node-metastasis. Source: From Gunderson et al.76 Copyright Elsevier. |
Once a colon or rectal carcinoma has been diagnosed, a staging evaluation should be undertaken. The colon must be evaluated for synchronous tumors, usually by colonoscopy. Synchronous disease will be present in up to 5% of patients. For rectal cancers, digital rectal examination and rigid or flexible proctoscopy with biopsy should be performed to assess tumor size, location, morphology, histology, and fixation. Endorectal ultrasound or MRI can be invaluable in staging rectal cancer and is used to classify the ultrasound T and N stage of rectal cancers (Fig. 29-24). A chest/abdominal/pelvic CT scan should be obtained to evaluate for distant metastases. Pelvic CT scan, and sometimes MRI, can be useful in large rectal tumors and in recurrent disease to determine the extent of local invasion. Among patients with obstructive symptoms, a water-soluble contrast study (Gastrografin enema) may be useful for delineating the degree of obstruction. It is important to avoid mechanical bowel preparation (for either colonoscopy or surgery) in a patient who appears to be obstructed. PET scan may be useful in evaluating lesions seen on CT scan and in patients in whom a risky or highly morbid operation is planned (pelvic exenteration, sacrectomy). Preoperative CEA is often obtained and may be useful for postoperative follow-up.
Endorectal ultrasonography showing a T3 rectal carcinoma. The dotted line is being used to measure the diameter of the lesion. (Used with permission of Charles O. Finne III, MD, Minneapolis, MN.)
Therapy for Colonic Carcinoma
The objective in treatment of carcinoma of the colon is to remove the primary tumor along with its lymphovascular supply. Because the lymphatics of the colon accompany the main arterial supply, the length of bowel resected depends on which vessels are supplying the segment involved with the cancer. Any adjacent organ or tissue, such as the omentum, that has been invaded should be resected en bloc with the tumor. If all of the tumor cannot be removed, a palliative procedure should be considered, although it important to note that “debulking” is rarely effective in colorectal adenocarcinoma.
The presence of synchronous cancers or adenomas or a strong family history of colorectal neoplasms suggests that the entire colon is at risk for carcinoma (often called a field defect), and a subtotal or total colectomy should be considered. Metachronous tumors (a second primary colon cancer) identified during follow-up studies should be treated similarly. However, the surgeon must be aware of which mesenteric vessels have been ligated at the initial colectomy because that may influence the choice of procedure.
The number of lymph nodes recovered in the surgical specimen has long served as a proxy for the oncologic adequacy of resection. A number of studies previously have suggested that a minimum of 12 lymph nodes in the resected specimen are necessary for adequate staging. In addition, patients in whom more nodes are harvested have better long-term outcome.76,77 As such, a 12-node minimum has been suggested as an appropriate benchmark for assessing quality of care. However, several investigators recently have called this into question, noting that the number of lymph nodes examined does not correlate with staging, use of adjuvant chemotherapy, or patient survival.70 Others have suggested that the number of negative lymph nodes and/or the lymph node ratio (positive lymph nodes to total lymph nodes) may further improve staging.77,78,79
If unexpected metastatic disease is encountered at the time of a laparotomy, the decision about whether to proceed with resection of the primary tumor depends on the volume of distant disease, location and size of the primary tumor, the operation required to remove the primary tumor, and the operative approach. If the metastatic disease is low volume (isolated or potentially resectable liver lesions) and the resection of the primary tumor is straightforward (segmental abdominal colectomy), it is probably reasonable to proceed with resection. On the other hand, if the metastatic disease is high volume (carcinomatosis), especially if the primary tumor is minimally symptomatic, the operation should be aborted in order to facilitate early systemic chemotherapy. Some centers favor starting the operation with a diagnostic laparoscopy in cases where risk of discovering metastasis is high in order to minimize the magnitude of the operation should surgery be aborted. With recent advances in chemotherapy, many of these patients will never develop a complication from the primary tumor requiring surgical intervention.81
Other palliative approaches include a bypass or proximal stoma for obstructing lesions.
Polyps containing carcinoma in situ (high-grade dysplasia) carry no risk of lymph node metastasis. However, the presence of high-grade dysplasia increases the risk of finding an invasive carcinoma within the polyp. For this reason, these polyps should be excised completely, and pathologic margins should be free of dysplasia. Most pedunculated polyps and many sessile polyps may be completely removed endoscopically. These patients should be followed with frequent colonoscopy to ensure that the polyp has not recurred and that an invasive carcinoma has not developed. In cases where the polyp cannot be removed entirely, a segmental resection is recommended.
Stage I: The Malignant Polyp (T1, N0, M0)
Occasionally a polyp that was thought to be benign will be found to harbor invasive carcinoma after polypectomy. Treatment of a malignant polyp is based on the risk of local recurrence and the risk of lymph node metastasis.64 The risk of lymph node metastases depends primarily on the depth of invasion. Invasive carcinoma in the head of a pedunculated polyp with no stalk involvement carries a low risk of metastasis (<1%) and may be completely resected endoscopically. However, lymphovascular invasion, poorly differentiated histology, or tumor within 1 mm of the resection margin greatly increases the risk of local recurrence and metastatic spread. Segmental colectomy is then indicated. Invasive carcinoma arising in a sessile polyp extends into the submucosa and is usually best treated with segmental colectomy (Fig. 29-25).
Levels of invasive carcinoma in pedunculated and sessile polyps. ca = carcinoma.
Stages I and II: Localized Colon Carcinoma (T1-3, N0, M0)
The majority of patients with stages I and II colon cancer will be cured with surgical resection. Few patients with completely resected stage I disease will develop either local or distant recurrence, and adjuvant chemotherapy does not improve survival in these patients. However, up to 46% of patients with completely resected stage II disease will ultimately die from colon cancer. For this reason, adjuvant chemotherapy has been suggested for selected patients with stage II disease (young patients, tumors with “high-risk” histologic findings). It remains controversial as to whether chemotherapy improves survival rates in these patients. Molecular profiling holds promise for improving patient selection in these early cancers.
Stage III: Lymph Node Metastasis (Tany, N1, M0)
Patients with lymph node involvement are at significant risk for both local and distant recurrence, and adjuvant chemotherapy has been recommended routinely in these patients. 5-Fluorouracil–based regimens (with leucovorin) and oxaliplatin (FOLFOX) reduce recurrences and improve survival in this patient population.69 It is important to note, however, that a subgroup of patients with stage III disease will do well without chemotherapy. MSI status in particular predicts good prognosis. Subset analysis from the CRYSTAL trial has shown that patients with MSI-high stage III disease do not benefit from 5-fluorouracil–based chemotherapy. Molecular profiling, therefore, may be helpful in determining which stage III patients can safely avoid systemic chemotherapy.82
Stage IV: Distant Metastasis (Tany, Nany, M1)
Survival is extremely limited in stage IV colon carcinoma. However, unlike many other malignancies, highly selected patients with isolated, resectable metastases may benefit from resection (metastasectomy). The most common site of metastasis is the liver. Of patients with systemic disease, approximately 15% will have metastases limited to the liver. Of these, 20% are potentially resectable for cure. Survival is improved in these patients (20% –40% 5-year survival) when compared to patients who do not undergo resection. Hepatic resection of synchronous metastases from colorectal carcinoma may be performed as a combined procedure or in two stages. All patients require adjuvant chemotherapy. The second most common site of metastasis is the lung, occurring in approximately 20% of patients with colorectal carcinoma. Although very few of these patients will be potentially resectable, among those who are (about 1%–2% of all colorectal cancer patients), long-term survival benefit is approximately 30% to 40%.83 There are limited reports of successful resection of metastases in other sites (ovary and retroperitoneum are most common).
The remainder of patients with stage IV disease cannot be cured surgically, and therefore, the focus of treatment should be palliation.84 Methods such as colonic stenting for obstructing lesions of the left colon also provide good palliation. More limited surgical intervention such as a diverting stoma or bypass procedure may be appropriate in patients with stage IV disease who develop obstruction. Hemorrhage in an unresectable tumor can sometimes be controlled with angiographic embolization. External beam radiation also has been used for palliation.
Therapy for Rectal Carcinoma
The biology of rectal adenocarcinoma is thought to be identical to the biology of colonic adenocarcinoma, and the operative principles of complete resection of the primary tumor, its lymphatic bed, and any other involved organ apply to surgical resection of rectal carcinoma. However, the anatomy of the pelvis and proximity of other structures (ureters, bladder, prostate, vagina, iliac vessels, and sacrum) make resection more challenging and often require a different approach than for colonic adenocarcinoma. Moreover, it is more difficult to achieve negative radial margins in rectal cancers that extend through the bowel wall because of the anatomic limitations of the pelvis. Therefore, local recurrence is higher than with similar stage colon cancers. However, unlike the intraperitoneal colon, the relative paucity of small bowel and other radiation-sensitive structures in the pelvis makes it easier to treat rectal tumors with radiation. Therapeutic decisions, therefore, are based on the location and depth of the tumor and its relationship to other structures in the pelvis.
The distal 10 cm of the rectum are accessible transanally. For this reason, several local approaches have been proposed for treating rectal neoplasms. Transanal excision (full thickness or mucosal) is an excellent approach for noncircumferential, benign, villous adenomas of the rectum. Transanal endoscopic microsurgery (TEM) and transanal minimally invasive surgery (TAMIS) make use of a specially designed proctoscope, magnifying system, and instruments similar to those used in laparoscopy to allow local excision of lesions higher in the rectum (up to 15 cm). Although this technique has been used for selected T1, and some T2, carcinomas, local excision does not allow pathologic examination of the lymph nodes and might therefore understage patients. Moreover, local recurrence rates are high after transanal excision, and salvage surgery, while often curative, is associated with poorer survival than with initial radical surgery. Local excision of any rectal neoplasm should be considered an excisional biopsy because final pathologic examination of the specimen may reveal an invasive carcinoma that then mandates more radical therapy.
Ablative techniques, such as electrocautery or endocavitary radiation, also have been used. The disadvantage of these techniques is that no pathologic specimen is retrieved to confirm the tumor stage. Fulguration is generally reserved for extremely high-risk patients with a limited life span who cannot tolerate more radical surgery.
Radical resection is preferred to local therapy for most rectal carcinomas. Radical resection involves removal of the involved segment of the rectum along with its lymphovascular supply. Although any microscopically negative margin has been suggested to be adequate, most surgeons still attempt to obtain a 2-cm distal mural margin for curative resections.
Total mesorectal excision (TME) is a technique that uses sharp dissection along anatomic planes to ensure complete resection of the rectal mesentery during low and extended low anterior resections. For upper rectal or rectosigmoid resections, a partial mesorectal excision of at least 5 cm distal to the tumor appears adequate. TME both decreases local recurrence rates and improves long-term survival rates. Moreover, this technique is associated with less blood loss and less risk to the pelvic nerves and presacral plexus than is blunt dissection. The principles of TME should be applied to all radical resections for rectal cancer.
Recurrence of rectal cancer generally has a poor prognosis. Extensive involvement of other pelvic organs (usually occurring in the setting of tumor recurrence) may require a pelvic exenteration. The rectal and perineal portions of this operation are similar to an APR, but en bloc resection of the ureters, bladder, and prostate or uterus and vagina are also performed. A permanent colostomy and an ileal conduit to drain the urinary tract may be necessary. The sacrum may also be resected if necessary (sacrectomy) up to the level of the S2-S3 junction. These operations are best performed in tertiary centers with multidisciplinary teams consisting of a colon and rectal surgeon, urologist, neurosurgeon, and plastic surgeon.
Diagnostic algorithm for rectal cancer. CT = computed tomography; MRI = magnetic resonance imaging; U/S = ultrasound.
Pretreatment staging of rectal carcinoma often relies on endorectal ultrasound to determine the T and N status of a rectal cancer. Ultrasound is highly accurate at assessing tumor depth, but less accurate in diagnosing nodal involvement. Ultrasound evaluation can guide choice of therapy in most patients. MRI is useful to assess mesorectal involvement. When the radial margin is threatened or involved, neoadjuvant chemoradiation is recommended.
Villous adenomas harboring carcinoma in situ (high-grade dysplasia) are ideally treated with local excision. A 1-cm margin should be obtained. Rarely, radical resection will be necessary if transanal excision is not technically possible (large circumferential lesions).
Stage I: Localized Rectal Carcinoma (T1-2, N0, M0)
Although local excision has been used for small, favorable sessile uT1N0 and uT2N0 rectal cancers, local recurrence rates may be as high as 20% and 40%, respectively. For this reason, radical resection is strongly recommended in all good-risk patients. Lesions with unfavorable histologic characteristics and those located in the distal third of the rectum, in particular, are prone to recurrence. In high-risk patients and in patients who refuse radical surgery because of the risk of need for a permanent colostomy, local excision may be adequate, but strong consideration should be given to adjuvant or neoadjuvant chemoradiation to improve local control. The efficacy of adjuvant or neoadjuvant chemoradiation followed by transanal excision in patients who can tolerate radical surgery has been controversial. Early results from ACOSOG Z6041, in which patients with T2 rectal cancers received neoadjuvant chemoradiation followed by transanal excision, showed a pathologic complete response rate of 44%. Long-term outcomes, however, are not yet known.85
Locally Advanced Rectal Cancer (Stages II and III)
Stage II: Localized Rectal Carcinoma (T3-4, N0, M0)
Larger rectal tumors, especially if located in the distal rectum, are more likely to recur locally. There are two schools of thought, each differing in their approach to control local recurrences. Advocates of total mesorectal resection suggest that optimization of operative technique will obviate the need for any adjuvant chemoradiation to control local recurrence after resection of stages I, II, and III rectal cancers. The opposing school suggests that stages II and III rectal cancers will benefit from chemoradiation. They argue that such therapy reduces local recurrences and prolongs survival whether given preoperatively or postoperatively. The advantages of preoperative chemoradiation include tumor shrinkage, increased likelihood of resection and of a sphincter-sparing procedure, tumor downstaging by treating locally involved lymph nodes, and decreased risk to the small intestine. Disadvantages include possible overtreatment of early-stage tumors, impaired wound healing, and pelvic fibrosis increasing the risk of operative complications. Postoperative radiation allows accurate pathologic staging of the resected tumor and lymph nodes and avoids the wound healing problems associated with preoperative radiation. However, bulky tumors, tumors involving adjacent organs, and very low rectal tumors may be much more difficult to resect without preoperative radiation and may require a more extensive operation.
Stage III: Lymph Node Metastasis (Tany, N1, M0)
Many surgeons now recommend chemotherapy and radiation either pre- or postoperatively for node-positive rectal cancers. The advantages and disadvantages are similar to those listed for stage II disease, except that the likelihood of overtreating an early-stage lesion is considerably less.
Over the past two decades, a wide variety of studies have addressed the issue of adjuvant and neoadjuvant therapy for locally advanced rectal cancer. Many of these studies demonstrated both improved local control and prolonged survival and resulted in the 1990 National Institutes of Health (NIH) consensus conference recommendation for postoperative chemoradiation therapy in these patients. There is little controversy regarding chemoradiation therapy for stage III (node-positive) disease. However, advances in surgical technique, such as TME, for locally advanced node-negative cancers (T3-4, N0; stage II) have improved local control with surgery alone, prompting some to abandon adjuvant chemoradiation in these patients, especially for those with cancers in the proximal rectum. Although the data from these studies are intriguing, other reports have shown that chemoradiation improves local control and survival even in patients who undergo TME. Thus, most colorectal surgeons in the United States continue to recommend adjuvant or neoadjuvant therapy for patients with locally advanced disease. Many European surgeons now rely heavily on MRI staging to determine the need for neoadjuvant chemoradiation. They use neoadjuvant chemoradiation if the radial margin is threatened or involved by the cancer or if anal sphincter or other local organ invasion is present. In the United States, chemoradiation therapy is still recommended for all patients with stage III disease and the majority of patients with stage II disease. In select patients with T3 tumors, favorable histology, and negative radial margins, chemoradiation may not be necessary, but larger prospective studies are required before this approach can be recommended.
Appropriate timing of chemoradiation for locally advanced rectal cancer has been debated. Historically, preoperative chemoradiation has been advocated based on tumor shrinkage/downstaging, improved resectability, and the possibility of performing a sphincter-sparing operation in some patients. In addition, the absence of small bowel adhesions in the pelvis may decrease toxicity. However, preoperative radiation therapy may increase operative complications and impairs wound healing. Although preoperative endorectal ultrasound and MRI have improved our ability to stage rectal cancer, clinical “overstaging” can be problematic, and neoadjuvant therapy may therefore overtreat patients with pT1-2, N0 tumors. Advocates of postoperative radiation therapy cite more accurate pathologic staging and fewer operative/postoperative complications. However, large, bulky tumors may be unresectable or require a more extensive operation (APR, pelvic exenteration) without preoperative therapy. In addition, postoperative pelvic radiation may compromise function of the neorectum.
Comparisons of perioperative toxicity and oncologic outcome have been addressed by the German CAO/ARO/AIO-94 trial. In this study, pre- and postoperative chemoradiation were associated with equivalent acute toxicity and equivalent postoperative complication rates. Postoperative chemoradiation, however, doubled the risk of postoperative stricture formation. In addition, preoperative chemoradiation halved the risk of local recurrence (6% vs. 12%). Based on these data, most surgeons consider preoperative chemoradiation to be the most appropriate therapy for locally advanced rectal cancer.86
Stage IV: Distant Metastasis (Tany, Nany, M1)
Like stage IV colon carcinoma, survival is limited in patients with distant metastasis from rectal carcinoma. Isolated hepatic and/or pulmonary metastases are rare, but when present may be resected for cure in selected patients.83 Some patients will require palliative procedures. Radical resection may be required to control pain, bleeding, or tenesmus, but highly morbid procedures such as pelvic exenteration and sacrectomy should generally be avoided in this setting. Local therapy using cautery, endocavitary radiation, or laser ablation may be adequate to control bleeding or prevent obstruction. Intraluminal stents may be useful in the uppermost rectum but often cause pain and tenesmus lower in the rectum. Occasionally, a proximal diverting colostomy will be required to alleviate obstruction. A mucus fistula should be created if possible to vent the distal colon. It is critical that the morbidity of any procedure be realistically weighed against potential benefit in these patients with limited life expectancy. The assistance of a palliative care team can be invaluable in this setting.84
Follow-Up and Surveillance
Patients who have been treated for one colorectal cancer are at risk for the development of recurrent disease (either locally or systemically) or metachronous disease (a second primary tumor). In theory, metachronous cancers should be preventable by using surveillance colonoscopy to detect and remove polyps before they progress to invasive cancer. For most patients, a colonoscopy should be performed within 12 months after the diagnosis of the original cancer (or sooner if the colon was not examined in its entirety prior to the original resection). If that study is normal, colonoscopy should be repeated every 3 to 5 years thereafter.
The optimal method of following patients for recurrent cancer remains controversial. The goal of close follow- up observation is to detect resectable recurrence and to improve survival. Re-resection of local recurrence and resection of distant metastasis to liver, lung, or other sites are often technically challenging and highly morbid, with only a limited chance of achieving long-term survival. Thus, only selected patients who would tolerate such an approach should be followed intensively. Because most recurrences occur within 2 years of the original diagnosis, surveillance focuses on this time period. Patients who have undergone local resection of rectal tumors probably also should be followed with frequent endoscopic examinations (every 3–6 months for 3 years, then every 6 months for 2 years). CEA is often followed every 3 to 6 months for 2 years. CT scans are often performed annually for 5 years, but there are few data to support this practice. More intensive surveillance is appropriate in high-risk patients such as those with possible HNPCC syndrome or T3, N+ cancers. Although intensive surveillance improves detection of resectable recurrences, it is important to note that a survival benefit has never been proven. Therefore, the risks and benefits of intensive surveillance must be weighed and treatment individualized.
Treatment of Recurrent Colorectal Carcinoma
Between 20% and 40% of patients who have undergone curative intent surgery for colorectal carcinoma will eventually develop recurrent disease. Most recurrences occur within the first 2 years after the initial diagnosis, but preoperative chemoradiation therapy may delay recurrence. While most of these patients will present with distant metastases, a small proportion will have isolated local recurrence and may be considered for salvage surgery. Recurrence after colon cancer resection usually occurs at the local site within the abdomen or in the liver or lungs. Resection of other involved organs may be necessary. Recurrence of rectal cancer can be considerably more difficult to manage because of the proximity of other pelvic structures. If the patient has not received chemotherapy and radiation, then adjuvant therapy should be administered prior to salvage surgery. Radical resection may require extensive resection of pelvic organs (pelvic exenteration with or without sacrectomy). Ideally, the aim of a salvage operation should be to resect all of the tumor with negative margins. However, if the ability to achieve a negative margin is in question, the addition of intraoperative radiation therapy (usually brachytherapy) can help improve local control. Pelvic MRI is useful for identifying tumor extension that would prevent successful resection (extension of tumor into the pelvic sidewall, involvement of the iliac vessels or bilateral sacral nerves, sacral invasion above the S2-S3 junction). Patients should also undergo a thorough preoperative evaluation to identify distant metastases (CT of chest, abdomen, and pelvis, and PET scan) before undergoing such an extensive procedure. Nevertheless, radical salvage surgery can prolong survival in selected patients.
Minimally Invasive Techniques For Resection
Laparoscopic colectomy for cancer has been controversial. Early reports of high port site recurrence dampened enthusiasm for this technique.87 The ability to perform an adequate oncologic resection for cancer has also been questioned. Several trials have laid to rest many of these fears. The Clinical Outcomes of Surgical Therapy Study Group (COST), the Colon Carcinoma Laparoscopic or Open Resection (COLOR) trial, and the United Kingdom Medical Research Council Conventional versus Laparoscopic-Assisted Surgery in Colorectal Cancer (CLASSICC) trial all have shown oncologic equivalence between open and laparoscopic techniques. In these multi-institutional studies, the rates of cancer recurrence, survival, and quality of life were similar, suggesting that, in the hands of an appropriately trained surgeon, laparoscopic colectomy is appropriate for cancer.87,88,89 The recent introduction of robotic surgery offers an additional minimally invasive approach. Early studies suggest that robotic surgery may be the oncologic equivalent to laparoscopic surgery for colorectal cancer. A prospective, randomized, multicenter trial, Robotic versus Laparoscopic Resection for Rectal Cancer (ROLARR) is under way in hopes of answering this question.91