The microanatomic location of metastatic melanoma in sentinel lymph nodes predicts nonsentinel lymph node involvement

Sentinel node biopsy is now widely accepted as the most accurate prognostic indicator in melanoma, and is important in guiding management of patients with clinical stage I or II disease. Patients with a positive sentinel node have conventionally undergone completion lymphadenectomy (CLND) of the involved basin, but only 20% have involvement beyond the sentinel node, suggesting that CLND may be unnecessary for the other 80% of patients. This study seeks to identify criteria that might be used to be more restrictive in selecting those who should undergo CLND.

A total of 146 patients were identified who had had a positive sentinel node biopsy for malignant melanoma. Their sentinel nodes and lymphadenectomy specimens were re-evaluated pathologically. The metastatic melanoma in each sentinel node was assessed according to its microanatomic location within the node (subcapsular, combined subcapsular and parenchymal, parenchymal, multifocal, or extensive), and this was correlated with the presence of involved nonsentinel nodes in the CLND. The depth of the metastases from the sentinel node capsule was also recorded.

The metastatic deposits in the sentinel node were subcapsular in 26.0% of patients. None of these patients had any nonsentinel nodes involved on CLND. In the patients whose sentinel node metastases had a different microanatomic location, the rate of nonsentinel node involvement was 22.2% overall.

The microanatomic location of metastases within sentinel nodes predicts nonsentinel lymph node involvement. In patients with only subcapsular deposits in the sentinel node, it is possible that CLND could safely be avoided.