Number of melanocytic nevi as a major risk factor for malignant melanoma.

A study of 121 melanoma patients and 139 control subjects from the University of California, San Francisco clinics was conducted among whites to examine the relationship between number of melanocytic nevi and cutaneous melanoma. Nevi that measured 2 mm or more in diameter were counted over the body by a dermatologist and a dermatology fellow. The average number of nondysplastic melanocytic nevi that were 2 mm or greater in diameter was 97 for melanoma patients and 36 for control subjects (p less than 0.001). Relative risks were 1.6 (p = 0.43) for 11 to 25 nevi, 4.4 (p = 0.01) for 26 to 50 nevi, 5.4 (p = 0.008) for 51 to 100 nevi, and 9.8 (p = 0.001) for more than 100 nondysplastic melanocytic nevi. Relative risks were 3.8 (p = 0.001) for 1 to 5 dysplastic nevi and 6.3 (p = 0.003) for 6 or more of these lesions. Report of blistering sunburns or of a previous skin cancer and having red or blond hair at the age of 20 were also independently associated with an increased risk of cutaneous melanoma. If confirmed in larger studies, the results presented on number of nevi and melanoma risk suggest a readily identifiable melanoma-prone group that could be followed to detect early malignant melanoma.