[Histologic analysis of intraepidermal melanocytic proliferation in the peripheral area of superficially diffused melanoma].

Histological analysis of intraepidermal melanocytic proliferation in the peripheral areas of superficial spreading melanoma. The intraepidermal melanocytic proliferation in the areas adjacent to the invasive component of 100 superficial spreading melanomas of the skin (levels III and IV) was studied. Three patterns were identified: 1) melanoma in situ type (MIS); 2) melanocytic dysplasia type (DYS); 3) normal skin or increased number of typical melanocytes (0). The different distribution of these patterns in the areas adjacent to the invasive melanoma led to a histological classification of the tumors into 4 topographical models. Two models showed MIS areas and contiguous normal skin (A1, A2); two models showed MIS areas adjacent to DYS areas, that in turn were contiguous to normal skin (B1, B2). In all cases, however, in centrifugal sense, more severe alterations preceded less severe ones. These observations suggest that superficial spreading melanoma grows horizontally by induction of neighbour cells (neoplastic recruitment). The neoplastic transformation seems to progress in two ways: directly to melanoma in situ or through an intermediate phase (melanocytic dysplasia).