Rationale of Sentinel Lymph Node Mapping and Biopsy
Early in the nineteenth century, Virchow implicated lymph nodes in the process of the local spread of solid tumors to a more widespread systemic disease. The node identified by Virchow is specifically located in the left supraclavicular region. In the modern vernacular, the term sentinel lymph node (SLN) describes the first lymph node to receive drainage from any solid tumor in any anatomic region. It was not until 1989 that the concept of SLN biopsy, as it is currently known, was first made popular based on studies by Morton et al.1 A feasibility study using blue dye was translated into a successful clinical trial in patients with melanoma. Their results indicated that biopsy and analysis of SLNs accurately reflected the tumor status of the lymph node basin. SLN biopsy was introduced in breast cancer patients shortly thereafter.2 Further studies supported SLN biopsy as a way to identify patients at highest risk for locoregional recurrence and metastatic spread, and, therefore, most likely to benefit from adjuvant therapy. SLN mapping aids in the identification of lymph nodes at highest risk of metastasis and allows for more detailed analysis to detect early metastatic disease thus identifying patients who may benefit from adjuvant therapy. While SLN biopsy is standard in both breast cancer and melanoma patients, a number of factors have led to slower adoption in patients with non-small cell lung cancer (NSCLC).
Nodal Disease in Lung Cancer
Lung cancer is the leading cause of cancer deaths among both men and women in the US, with an estimated 170,000 new cases and 160,000 deaths reported each year.3 Even in patients with stage I disease thought to have undergone curative resection, recurrence rates remain high at nearly 40%.4 This high incidence of recurrent disease in stage I lung cancer patients suggests that these patients are currently understaged and undertreated. In fact, retrospective analysis has demonstrated that nearly 15% to 20% of N0 patients harbor “occult” metastatic disease when nodes are histologically scrutinized in the manner done for breast cancer and melanoma.5 Not surprisingly, patients with occult nodal disease exhibit poorer survival and increased rates of recurrence. Despite all the recent clinical advances in lung cancer therapy, the best predictor of patient outcome following surgical resection remains the presence or absence of metastatic disease to lymph nodes. To improve survival of patients with surgically resectable lung cancer, detailed intraoperative lymph node evaluation is needed to more accurately stage patients and identify candidates for early adjuvant therapy.
SLN mapping seeks to identify the first lymph node to harbor metastatic disease from a nearby tumor and has become an integral part of patient selection for adjuvant treatment in solid malignancies such as breast cancer and melanoma. The two primary benefits of SLN mapping in breast cancer and melanoma have been (1) limiting the extent of lymph node dissection ...