Melanocytic nevus development in Colorado children born in 1998: a longitudinal study.

OBJECTIVE To describe the development of nevi from 3 to 8 years of age in a birth cohort of children in Colorado. DESIGN Longitudinal observational study. SETTING Large managed care organization and university and private primary care practices. PARTICIPANTS Annual convenience samples of children born in 1998 (range, n = 137 to n = 870) (participation rates, 18.8%-76.0%). We recruited children through the managed care organization, private primary care practices, and community settings. MAIN OUTCOME MEASURES Total whole body nevus counts, counts by nevus diameter (< 2, 2 to < 5, or > or = 5 mm), and counts for chronically and intermittently exposed body sites. RESULTS Non-Hispanic white children had significantly more nevi than did other racial/ethnic groups and developed an average of 4 to 6 new nevi per year from 3 to 8 years of age. Non-Hispanic white boys had significantly more nevi than did girls beginning at 6 years of age (median, 21 [interquartile range, 28] vs 17 [17]; P = .002). This difference was due to nevi of less than 2 mm and nevi in chronically exposed body sites. Development of new nevi leveled off in chronically exposed body sites at 7 years of age and at a higher level for boys than girls. CONCLUSIONS Children in Colorado developed more small nevi and fewer large nevi compared with children in other regions of the world, highlighting the importance of studying nevus development in various locations where sun exposure patterns and behavioral norms vary. The sex difference in nevus development could be owing to variation in sun exposure and/or a biological predisposition of boys to develop more nevi. Studies of nevus development can aid in the understanding of the complicated relationship between nevus development and malignant melanoma.