Sentinel Lymph Node

A relatively new development in the surgical management of the clinically negative regional lymph node basin is the introduction of lymphatic mapping technology. Lymphatic mapping and sentinel lymph node biopsy were first reported in 1977 by Cabanas for penile cancer.194 Morton and colleagues implemented this approach for the treatment of melanoma,195 and Giuliano and colleagues further adapted the technology to breast cancer.196 Now sentinel node biopsy is the standard of care for the management of melanoma and is rapidly becoming the standard of care in breast cancer. Moreover, the utility of sentinel node biopsy is being explored in other cancers such as esophageal, gastric, colon, and head and neck cancers.

The first node to receive drainage from the tumor site is termed the sentinel node. This node is the node most likely to contain metastases, if metastases to that regional lymph node basin are present. The goal of lymphatic mapping and sentinel lymph node biopsy is to identify and remove the lymph node most likely to contain metastases in the least invasive fashion. The practice of sentinel lymph node biopsy followed by selective regional lymph node dissection for patients with a positive sentinel lymph node avoids the morbidity of lymph node dissections in patients with negative nodes. An additional advantage of the sentinel lymph node technique is that it directs attention to a single node, allowing more careful analysis of the lymph node most likely to have a positive yield and increasing the accuracy of nodal staging.202

Two criteria are used to assess the efficacy of a sentinel lymph node biopsy: the sentinel lymph node identification rate and the false-negative rate. The sentinel lymph node identification rate is the proportion of patients in whom a sentinel lymph node was identified and removed among all patients undergoing an attempted sentinel lymph node biopsy. The false-negative rate is the proportion of patients with regional lymph node metastases in whom the sentinel lymph node was found to be negative. False-negative biopsies may be due to identification of the wrong node or to missing the sentinel node (i.e., surgical error), or they may be due to the cancer cells establishing metastases not in the first encountered node, but in a second echelon node (i.e., biologic variation). Alternatively, false-negative biopsies may be due to inadequate histologic evaluation of the lymph node. A sentinel lymph node can be identified in almost 100% of melanoma patients and in 94% of breast cancer patients. The false-negative rates for sentinel lymph node biopsy in larger series range between 0 and 11%. Both increases in the identification rate and decreases in the false-negative rate have been observed as surgeons gain experience with the technique. For breast cancer, therefore, it is recommended that until a surgeon documents an identification rate of greater than 90% and a false-negative rate of less than 5%, he or she should continue to perform concomitant axillary dissections.

Lymphatic mapping is performed by using isosulfan blue dye, technetium-labeled sulfur colloid or albumin, or a combination of both techniques to detect sentinel nodes. The combination of blue dye and technetium has been reported to improve the capability of detecting sentinel lymph nodes. The nodal drainage pattern usually is determined with a preoperative lymphoscintogram, and the "hot" and/or blue nodes are identified with the assistance of a gamma probe and careful nodal basin exploration. Careful manual palpation is a crucial part of the procedure to minimize the false-negative rate. The nodes are evaluated with serial sectioning, hematoxylin and eosin staining, and immunohistochemical staining with S-100 and HMB-45 for melanoma and cytokeratin for breast cancer.

In spite of widespread use of lymphatic mapping, there are still controversies about some technical aspects such as how many nodes should be removed. Other controversies that remain in lymphatic mapping for breast cancer include the roles of lymphoscintigraphy, internal mammary nodal mapping, and immunohistochemistry, and the indications for completion of node dissection. The uses of sentinel node biopsy after an excisional biopsy in patients with large breast tumors, in patients who have received preoperative chemotherapy, and in patients with multicentric disease also have been controversial. However, it is increasingly apparent that, although these patients may have a higher risk for a false-negative sentinel node, the accuracy is still high enough to justify sentinel node biopsy in most patients.