The histological variance of malignant melanoma: the interrelationship of histological subtype, neoplastic progression, and biological behaviour

Summary Histological variance within premalignant melanocytic dysplasias and melanomas reflects the biological progression of neoplasia. In general, the more severe cytological atypia, the more advanced the stage of neoplasia, and the more likely true melanomatous transformation (vertical growth or level III invasion) will be present. Histological variance may be seen in disparity between the cytology of the premalignant precursor and the vertical growth component and in the expression of normally latent phenotypic options such as desmoplasia and neurotropism. The pattern of superficial spreading melanoma (severe atypism, large epithelioid cells in pagetoid growth) is universal and qualifies as the common final pathway. Breslow's criteria of measurement are useful in formulating therapy in melanomas showing the common final pathway but may not accurately relate to the biological potential of minimal deviation variants i.e. those with mild to moderate melanocytic atypia. Examples of such variants are lentigo maligna melanoma, melanomas arising in pigmented spindle cell nevus, Spitz nevus, cellular blue nevus, dermal nevus and melanomas histologically resembling halo nevus.