Histological type and biological behavior of primary cutaneous malignant melanoma. 1. An analysis of 1916 cases.

In 1916 patients with primary malignant melanoma of the skin (excluding palms, soles, and nailbeds) the primary lesions were reviewed microscopically and classified according to Clark's system into lentigo maligna melanoma (85), superficial spreading melanoma (1234), and nodular melanoma (513). Differentiation between the types was not possible in 84 melanomas (4%). By correlating type of melanoma with various clinical and histological features, it was found that the 3 types differed significantly from one another with regard to growth rate of tumor, antecedent nevus, dominant type of invasive tumor cell, and prognosis. The study thus supported the basic principle of the classification employed, that the 3 histological types represent distinct entities of cutaneous melanoma with different clinical, cellular, and behavioral characteristics. As originally described by Clark, the growth rate was greatest for nodular melanoma, followed by superficial spreading melanoma, and least for lentigo maligna melanoma. It is recommended that this classification be employed in the histological typing of cutaneous melanoma as 1) it is readily applied to the vast majority of melanomas, and 2) it seems to delineate separate clinico-pathologic entities of cutaneous melanoma, which might be correlated with aetiological differences.