Histopathological patterns of melanoma metastases in sentinel lymph nodes

Sentinel lymph node biopsy (SLNB) is an important component in the staging and treatment of cutaneous melanoma (CM). The medical literature provides only limited information regarding melanoma sentinel lymph node (SLN) histology. This report details the specific histological patterns of melanoma metastases in sentinel lymph nodes (SLNs) and highlights some key factors in evaluating SLNs for melanoma.

From 281 SLNB cases between June 1998 and May 2002, 79 consecutive cases of SLN biopsies positive for metastases from CM were retrospectively reviewed. The important characteristics of the SLNs and the metastatic foci are described.

The median size of positive SLNs was 17 mm (range, 5-38). SLNs had a median of two metastatic foci (range, 1-11), with the largest foci being a median of 1.1 mm in size (range, 0.05-24). S-100 and HMB-45 staining was positive in 100% and 92% of the detected metastatic foci, respectively. The metastatic melanoma cells were epithelioid, spindled, and mixed in 86%, 5%, and 9% of cases. Metastatic foci were most often (86%) found in the subcapsular region of the SLN. Benign naevic cells were found coexisting in 14% of positive SLNs.

Staining for S100 is more sensitive than HMB-45 (100% v 92%), but HMB-45 staining helped to distinguish benign naevic cells from melanoma. The subcapsular region was crucial in SLN evaluation, because it contained the metastases in 86% of cases. Evaluation of the subcapsular space should not be compromised by cautery artefacts or incomplete excision of the SLN.