C-KIT RECEPTOR EXPRESSION IN CUTANEOUS MALIGNANT-MELANOMA AND BENIGN MELANOCYTIC NEVI

To investigate the role of c-KIT receptor in melanocytic tumour develo pment and progression, we analysed the expression and localization of c-KIT by Immunohistochemistry and Western blotting. In contrast to the positive staining shown by melanocytes and naevus cells in the epider mis of common naevi (n = 20), all dysplastic naevi (n = 13) were negat ive, as were dermal melanocytic cells of blue naevi (n = 4) and common naevi (n = 26). Three out of four superficial spreading melanomas los t c-KIT expression both in the epidermal and dermal parts, while nodul ar melanomas showed no expression of c-KIT except in partially positiv e cells, and six out of seven metastatic melanomas were negative. In a cral lentiginous melanomas (n = 8), in contrast to other types of mela noma, all cases with melanoma cells growing basally in the epidermis s howed strong c-KIT positivity, but melanoma cells growing at the upper layers of the epidermis and vertically into the dermis lost c-KIT exp ression. Using the Western blot method on cultured pigment cells, huma n epidermal melanocytes, junctional naevus cells and one out of three metastatic melanoma cell lines showed 125 and 145 kDa bands correspond ing to c-KIT, whereas dermal naevus cells did not. These results sugge st that dysplastic naevi are distinct from ordinary naevi in terms of c-KIT expression and that basally growing cells in acral lentigenous m elanomas could be at an initial stage of tumour progression, before c- KIT loss occurs.