A new look at nevus-associated melanomas.

The frequency with which malignant melanomas arise in association with preexisting melanocytic nevi has been studied extensively. We opted to evaluate new aspects of this association. In particular, we addressed the relative proportions of acquired versus congenital nevi involved and categorized the acquired nevi according to morphological type. Approximately 23% of the melanomas (29 of 124) in this group arose in association with preexisting nevi of which 55% (n = 16) were acquired and 28% (n = 8) were congenital (small). In 17% (n = 5) a distinction could not confidently be made. Of the acquired nevi, the vast majority were of Clark's type. It is clear that a relatively small proportion of melanomas as a whole are associated with preexisting nevi, and this number should be kept in perspective in devising strategies for early detection and prevention. The involvement of Clark's nevi in this regard is known, but to date the role of small congenital nevi has been underrecognized.