A retrospective histological study of 669 cases of primary cutaneous malignant melanoma in clinical stage I. The consequences of a reclassification of the original group of lentigo maligna melanomas.

A selected series of primary malignant melanoma of the skin, clinical stage I, was originally classified according to Clark's system. The consistency of this classification was tested by two Brisbane pathologists who indicated that we had misinterpreted some cases of superficial spreading malignant melanoma as lentigo maligna melanoma. We have therefore reclassified the original group of 86 lentigo maligna melanomas. This resulted in a total series of 37 (5.5%) lentigo maligna melanomas, 301 (45%) superficial spreading malignant melanomas, 194 (29%) nodular malignant melanomas (unchanged) and 137 (20.5%) unclassifiable malignant melanomas. The diagnosis of lentigo maligna melanoma was not made unless the epidermis was atrophic and dermal solar elastosis was present. The new group of lentigo maligna melanomas is dominated by cases on the head among patients over 50 years of age (especially women). This is in better agreement with other studies than our previous findings. The relationship with tumour cell type, pigmentation, mitotic count, atypia, transsectional profile, level of invasion, ulceration, vascular invasion, lymphocyte infiltration and prognosis shown by the new groups of lentigo maligna melanoma and superficial spreading malignant melanoma indicates that the cases by which the diagnosis has been changed are relatively benign. Our previous conclusions are still valid. The lentigo maligna melanoma is still the most benign type and nodular malignant melanoma still the most malignant type of melanoma. The superficial spreading malignant melanoma still represents an intermediate tumour type, although it has deviated in the benign direction.