Diagnosis: Sentinel Lymph Node
• A sentinel lymph node is the first draining lymph node functionally determined with the use of a dye or other tracers. Its clinical applicability is based on the generally stepwise progression of metastasis in 95% to 98% of cases.
• The protocol for cutting sentinel lymph nodes is more rigorous than routine lymph node examination. Sentinel lymph nodes typically are examined at three levels with hematoxylin-eosin to reduce the false-negative rate (to 5% to 7%). It is generally recommended to cut sentinel lymph nodes grossly into 2- to 3-mm thick sections, if not thinner, rather than merely bisecting the lymph node. Bisection may be appropriate for nodes that are 4 to 5 mm in thickness but not for larger nodes because they would yield larger segments. A more judicious gross cutting of lymph nodes results in a lower rate of false-negative results and increases the likelihood of detecting metastasis.
• Although two to three lymph nodes on average are identified in a sentinel lymph node excision, fewer or more lymph nodes occasionally may be identified.
• The sensitivity of detection of metastasis in sentinel lymph nodes in an intraoperative setting depends on the size of the primary tumor. The tumor size predicts the likelihood of micrometastasis, which has a sensitivity of detection much lower than that of a macrometastasis.
• ACOSOG Z0011 is a randomized trial of axillary node dissection in women with clinical T1-2N0M0 breast cancer who have a positive sentinel node. In this trial, patients with clinically negative axillary nodes who had one or two sentinel lymph nodes positive for cancer were randomly assigned for either completion node dissection or observation without axillary therapy. Most patients received chemotherapy. The outcome suggested similar (noninferiority) recurrence rate and overall survival in the two study arms putting into question the need to complete the node dissection under these circumstances.
• ACOSOG Z0010 is a multicenter prognostic study of sentinel node and bone marrow micrometastases in women with clinical T1/T2N0M0 breast cancer. Among women receiving breast-conserving therapy and sentinel lymph node dissection, immunohistochemical evidence of sentinel lymph node metastasis was not associated with overall survival over a median of 6.3 years, whereas occult bone marrow metastasis, although rare, was associated with decreased survival. This study put into question the utility of performing cytokeratin immunohistochemistry on sentinel lymph nodes if nodes are negative by hematoxylin-eosin, given similar survival of patients who are immunohistochemistry negative.
