Comparison of S-100 versus hematoxylin and eosin staining for evaluating dermal invasion and peripheral margins by desmoplastic malignant melanoma

Desmoplastic malignant melanoma (DMM) is a rare and locally aggressive variant of malignant melanoma, which is difficult to diagnose clinically and microscopically. A retrospective study of 21 DMM were collected during 7 years, representing 1.7% of melanomas. By comparing S-100 and hematoxylin and eosin (H & E) staining in DMM, we sought to determine whether S-100 staining offered a more accurate means of assessing dermal and neural invasion, tumor thickness, and peripheral margins. Eleven cases were excluded because the tumor extended past the deep margin. Six cases that were stained with S-100 showed a greater tumor thickness than by H & E (difference of 0. 13 to 2.79 mm). In two cases, the tumor thickness was greater by using H & E than S-100, and there was no difference in the remaining two cases. Of the eight cases in which the peripheral margins were positive by S-100, neoplastic cells were only apparent at those margins in four cases when examined with H & E. The remaining two cases showed negative margins by both stains. Clinical follow-up was obtained from nine cases, and none had recurrence of melanoma. Particularly for hypocellular and amelanotic tumors, S-100 staining proved to be a valuable adjunct in determining the extent of the tumor at the peripheral margins.