The classification of malignant melanoma and its histologic reporting

Abstract

Apart from the rare malignant melanomas occurring in blue nevi, primary cutaneous malignant melanoma arises in 1 of 3 ways, regardless of the presence or absence of a pre-existing nevus. These three types have been designated: 1. Malignant melanoma, invasive, with adjacent intra-epidermal component of Hutchinson's melanotic freckle type; 2. Malignant melanoma, invasive, with adjacent intra-epidermal component of superficial spreading type; and 3. Malignant melanoma, invasive, without adjacent intra-epidermal component. Occasionally, both clinically and histologically, there may be difficulty in deciding whether a malignant melanoma belongs to category 1 or 2, but, in the majority of cases, these 2 types can be quite readily distinguished. In addition to recording the histogenetic mode of development of a malignant melanoma, a histologic system of reporting is recommended which includes mitotic activity, levels of invasion, and vascular involvement. There are other parameters such as the cell type, pigmentation, lymphocytic infiltrates, evidence of spontaneous regression, associated nevi, and solar changes in the dermis, all of which are of unknown significance. The recording of these features, which are clearly of interest for research purposes, is left to individual discretion. It is emphasized that all the usual macroscopic descriptions and measurements should continue to be recorded.