Multiple common naevi in Israeli adolescents.

The most prominent known phenotypic risk factor for the development of melanoma is a large number of common melanocytic naevi. The aims of this study were to determine the prevalence of multiple common naevi in a group of 17-year-olds and to identify possible associated risk factors. The study subjects were approximately 40,000 female and 60,000 male 17-year-old Jewish Israelis presenting to army recruitment centres for compulsory military service during a 1-year period from January 2003 to December 2003. Data were gathered on whole-body naevi count, years of education, place of residence and place of birth of the recruit, his/her parents and paternal grandparents. The count of whole-body naevi was carried out by military physicians. The multiple naevi phenotype was defined by the presence of more than 50 naevi. The prevalence of the phenotype was highest amongst recruits of American origin and lowest amongst those of Asian and African origin (P < 0.0001). The prevalence differed in different population centres, the highest being in the coastal cities of Haifa and Tel Aviv. This pattern corresponded to the geographical distribution of melanoma in Israel. Amongst male conscripts, the phenotype was more common in the better educated group (> or =12 years) than in the poorer educated conscripts (< or = 11 years) (P = 0.051). When adjusted for the factors studied, a significant correlation was found between a high multiple common naevi count and American and European origin and residence in coastal cities, reflecting the complex interplay between endogenous and exogenous factors of melanoma.