Solar nevogenesis: A surrogate for predicting a rise in incidence of malignant melanoma because of ozone depletion

Several case-control studies have shown that the risk for development of a malignant melanoma (MM) isproportionalto the number ofmelanocytic neviborneby a person.1-3 Accordingto Hollyet al.,4 the risk of MM increases with the number of nevi: relative risksare 1.6(p =0.43) for 11 to 25 melanocytic nevi, 4.4 (p = 0.01) for 26 to 50 nevi, 5.4 (P =0.008) for 51 to 100nevi, and 9.8 (p = 0.001) for 1 to 5 dysplastic nevi and 6.3 (p =0.003) for 6 or more dysplastic nevi. The anatomic distribution of melanocytic nevi, favoring sun-exposed rather than sun-protected areas of the skin, implies their solar induction(i.e., solar nevogenesis).5-12 An increased numberof melanocytic nevi is seen in geographic regions of higher insolation.l3, 14 In addition, the number of nevi is increasedin immunosuppressed patientsl5,16 and UV irradiation causes cutaneous immunosuppression.l" Melanocytic nevi are congenital or acquired. Most of the latter appearduring the first20 years of life. Acquired nevi, which are far more common than congenital nevi, can be subdivided into those induced bysun exposure (i.e., solarnevogenesis) and those lesscommonmelanocytic nevi that are not related to sun exposure.l ''