Atypical cells in human cutaneous re-excision scars for melanoma express p75NGFR, C56/N-CAM and GAP-43: evidence of early Schwann cell differentiation

Background: A common problem in the routine examination of melanoma re-excision scars occurs when a few or rare mildly atypical cells are present within the scar, raising the question of residual disease. Little is known about the derivation of these cells. Because the normal cutaneous wound-healing process is reparative, we hypothesized that these atypical cells may be reactive proliferating Schwann cell precursors. Methods: The expression of the Schwann cell differentiation markers p75NGFR, CD56/N-CAM and GAP-43 was examined by immunohistochemistry in scars of wide local re-excisions for melanoma and non-melanoma tumors. Expression of S100, gp100 (with HMB45) and MART1 was also analyzed by immunohistochemistry. Results: All melanoma and non-melanoma re-excision specimens contained mildly atypical, spindled or epithelioid cells within the scar. They varied in number from case to case and expressed S100, p75NGFR, CD56/N-CAM or GAP-43 but not gp100 (with HMB45) or MART1. Rare epithelioid non-melanoma cells within the superficial dermis expressed MART-1. Conclusions: Atypical cells are present in re-excision scars from melanoma and non-melanoma cases. They demonstrate early Schwann cell differentiation and appear to proliferate during the scarring process. The use of anti-MART-1 alone in the examination of melanoma re-excisions specimens may be inadequate as it may label rare, superficially located, non-melanoma cells within the scar.