“Microscopic satellites” are more highly associated with regional lymph node metastases than is primary melanoma thickness

A multivariate analysis was performed on 20 clinical and histologic variables from 327 Stage I prospectively studied melanoma patients who underwent elective regional lymph node dissection (ERLD). Primary tumor thickness, microscopic satellites, and the elapsed interval between diagnosis and ERLD, were selected as the combination of variables that were most highly associated with clinically occult regional lymph node metastases (P = 10−15, model chi-square). Microscopic satellites were defined as tumor nests, >0.05 mm in diameter, in the reticular dermis, panniculus, or vessels beneath the principal invasive tumor mass but separated from it by normal tissue on the section in which the Breslow measurement was taken. The probability of finding nodal metastases for melanomas <0.75 mm thick was 0% (0/41 patients); for those 0.76–1.50 mm, 4% (4/108); 1.51–3.0 mm, 14% (14/102); and >3.0 mm, 39.5% (30/76). Primary melanomas >1.50 mm thick with microscopic satellites were more often associated with nodal metastases than those of similar thickness without satellites (30/57 (53%) versus 14/121 (12%), P = 0.01). Some satellites probably represent intraspecimen metastases, while others do not. Any predictive model for occult regional lymph node metastases based on data from ERLD done <50 days after diagnosis may underestimate the prevalence of metastases.