Nevi as Risk Factors for Melanoma

There is a wide range of metanocytic nevi, sotne more prevalent in children than in aduits. Some, but not all, may be true precursors to melanoma and others may be markers of an individual at increased risk of developing melanoma on any body site. The mechanisms for such associations and the risk factors for developing nevi in the first place are currently the subjects of active research. The two groups of nevi currently recognized as potential precursors of melanoma are the giant congenital nevi and the so-called dysplastic or clinically atypical nevi. Giant congenital nevi are rare, and reports of malignant change are difficult to relate to their true prevalence. One of the few epidemiologic studies in this area came from Scandinavia, where a cohort of individuals was followed for several decades, with the lifetime risk of malignant change in the region of 4% to 6% (1). One of the difficulties of managing children with giant congenital nevi and trying to note malignant change is detecting this change in a heavily pigmented area that often has additional textural abnormalities in the epidermis and dermis. By the time change is visible or, more likely, palpable, the melanoma is frequently relatively advanced. A second problem relates to the associated melanocytosis of the central nervous system, which is commonly found in association with giant congenital nevi, particularly those that overlie the back of the scalp and neck area. Malignant change in these components is recorded and is virtually impossible to identify early. Advances in plastic surgical techniques over the past decade, particularly the use of tissue expanders, has made it possible to excise lesions that previously were considered inoperable. It remains to be seen whether or not this reduction in total quantity of nevus cells will reduce the risk of malignant change, but there is every reason to anticipate that this will be the case. Good follow-up registers are required to detect these improvements. A second approach to mans^ing these large nevi is to shave the area in the early neonatal period. This approach is based on the observation that a higher proportion of nevus cells are seen in the upper dermis in neonates than in older infants. Only a small number of centers carry out this procedure at present, and again longer-term follow-up is required to detect any changes. Both of these approaches to management of giant nevi should improve the child's cosmetic appearance, and thus the psychologic problems associated with the lesions. These problems should not be underestimated. Currently, relatively few data are available on the malignant potential of intermediate-size and small congenital nevi. We carried out a study looking at features of both the patients and the lesions in 95 individuals who developed melanoma prior to their thirtieth birthday (2). A very much higher than expected proportion of these individuals (42) had either clinical or pathologic evidence of a small earlyonset nevus (present before age 2 yrs) at the site of the melanoma. In addition, a higher than expected frequency of nevus ceils was reported in excised melanoma specimens (3). What is not known is the frequency of malignant change in the entire population of those who have small congenital nevi. The ethics and logistics of a study to determine this are so complicated that it is unlikely that this will ever be known with accuracy. At present, however, the frequency with which this is observed, bearing in mind that We of newboms have a congenital nevus, is not so great that prophylactic excision of all these lesions should be advocated.