Colon cancers are usually exophytic lesions that grow into the lumen of the colon. Their vascular nature makes them friable, often causing them to bleed.
Most colon cancers are distinguishable from surrounding mucosa by their color and texture, as seen here.
As colon cancers grow, they often grow in two directions—into the submucosal and deeper layers of the colon wall, as well as into the lumen, causing obstruction of the colon, as seen here. In this case, the colonoscope could not be passed more proximally due to the obstruction caused by the cancer.
If the colon cancer is causing obstructive symptoms, located in the rectum or sigmoid colon, and the patient is not a good surgical candidate, an expandable stent may be endoscopically placed to relieve obstruction, as in this case. In some instances, a stent may be placed temporarily to relieve obstruction prior to a resection of the cancer.
Many colon cancers will ulcerate as they grow exophytically into the lumen of the colon. They also tend to grow asymmetrically. Note how this cancer is asymmetric in its exophytic growth as well as the ulcer associated within it.
Occasionally, a colon cancer may appear more as an ulcer than an exophytic mass. This ulcerated cancer was suspicious for being malignant due to its location in the ascending colon in a patient without a history of inflammatory bowel disease. Occasionally, large benign ulcers of the rectum (stercoral ulcers) may be suspicious for malignancy.
This ulcerated, saddle-shaped lesion proved to be a small adenocarcinoma. The presence of an excavated, ulcerated surface of a broad based small mass was a clue to the malignant nature of this lesion.
Small carcinoid tumors often resemble small benign polyps. These are nearly always found in the rectum. ...