The classification of primary cutaneous malignant melanoma. A prospective study of 60 cases using Clark's classification.

A series of 60 primary cutaneous malignant melanomas has been studied by serial block technique. The resulting 492 sections have been classified as junctional naevus with or without atypia and preinvasive or invasive malignant melanoma according to Clark (1967). No sections showed lentigo maligna (melanoma). The overall classification resultedin 49 superficial spreading malignant melanomas, 6 nodular malignant melanomas and 5 unclassifiable malignant melanomas. In 3 cases (5%) there was inconsistency between the classification of the central section and the overall classification of the tumour. Five theoretical growth patterns have been postulated ranging from thatof the pure superficial spreading malignant melanoma completely surrounded by a preinvasive area to the pure nodular malignant melanoma which completely lacks any such area. Borderline cases between these two types certainly seem to exist. Features such as intraepidermal Pagetoid growth of tumour cells, co-existence of a benign melanocytic component and histological changes indicating tumour regression have been discussed. It is recommended that at least 3 tissue blocks should be taken from all malignant melanomas up to 25 mm in diameter and more if the tumour is larger.