The amount of metastatic melanoma in a sentinel lymph node: Does it have prognostic significance?

Background: The amount of metastatic disease in the sentinel lymph node (SLN) is examined as a prognostic factor in malignant melanoma. Methods: SLN mapping was performed on 592 patients with stage I and II malignant melanoma from March I, 1994, through December 31, 1999. One hundred four patients were found to have 134 sentinel SLNs containing metastatic melanoma. The slides were reviewed, and the size of the metastatic melanoma in each SLN was measured. The size of the metastatic deposit was defined as macrometastasis (>2 mm), micrometastasis (less than or equal to2 mm), a cluster of cells (10-30 grouped cells) in the subcapsular space or interfollicular zone, or isolated melanoma cells (1 to greater than or equal to20 individual cells) in subcapsular sinuses. Results: The number of metastases in each SLN was isolated melanoma cells, n = 5 (3.7%); cluster of cells, n = 35 (26.1%); less than or equal to2 mm, n = 45 (33.6%); and >2 mm, n = 49 (36.7%). Seventy-nine patients (76%) had a single positive SLN. The size of the largest nodal metastasis was used to stratify patients with multiple positive SLNs. The overall 3-year survival for patients with SLN micrometastases was 90%, versus 58% for patients with SLN macrometastases (P = .004). Conclusions: The amount of metastatic melanoma in an SLN is an independent predictor of survival. Patients with SLN metastatic deposits >2 mm in diameter have significantly decreased survival.