Risk of malignant transformation of congenital melanocytic nevi in blacks.

The risk of small congenital melanocytic nevi (CMN) developing into melanoma is not known, but is highly controversial. The frequency of small CMN is, paradoxically, slightly higher in some populations, such as blacks, who are at a lower risk of developing melanoma than whites. An estimate of the risk of malignant transformation of CMN in such a low-risk population could help in the management of congenital nevi in these patients and might also shed light on the inherent malignant risk of small CMN. We used a national population-based cancer registry, the Surveillance, Epidemiology, and End Results program (SEER), and the incidence of CMN in blacks taken from published newborn surveys to calculate a risk of malignant transformation. We calculated a maximum risk using a model based on a worst-case scenario, assuming that all melanomas on glabrous skin arise in CMN. We also calculated a modified risk based on the known historical association of nevi and melanomas in blacks, and estimates of the histologic association of the two. The cumulative maximum risk of malignant transformation in blacks to age 75 years was 1 in 164. It was strongly age dependent, with the majority occurring in persons over age 45. The estimated maximum risk before age 15 was less than 1 in 10,000 CMN, and in blacks age 15 to 35 less than 1 in 3700 CMN. The modified risk suggests that the worst-case scenario overestimates the risk by at least a factor of 12, making the actual risk in blacks up to age 75 approximately 1 in 2000.(ABSTRACT TRUNCATED AT 250 WORDS)