Do all melanomas come from "moles"? A study of the histological association between melanocytic naevi and melanoma.

Histological examination of 1101 melanomas (990 superficial spreading and 111 nodular melanomas) from 1098 people revealed that 23.3% showed an associated melanocytic naevus. Of these, 56.5% were classified histologically as common acquired, 37.7% as dysplastic and 5.8% as congenital. Of the superficial spreading melanomas, 25.7% showed an associated naevus. By contrast, only 2.7% of nodular melanomas showed histological evidence of a coexisting naevus. When the superficial spreading melanomas were analysed by level, the presence of a naevus varied from 31.3% of level I melanomas to 21.3% of level IV melanomas. When thickness was measured, an associated naevus was found in 27.0% of superficial spreading melanomas less than 1.0 mm thick, and 14.8% of melanomas with a thickness of 1.0 mm or greater. These data suggest that most melanomas do not arise in pre-existing naevi, and accordingly public educational programs for the early detection of melanoma should focus on looking for changes in previously normal skin as well as in pre-existing moles.