Development of melanocytic nevi in the first three years of life.

Interest in melanocytic nevi (moles) stems from their clinical, histologic, and epidemiologic association with melanoma. Few studies of nevi have been longitudinal (1,2), and all, apart from our own (3), have involved subjects 3 years old or older. Hence, little is known about the age at which nevi begin to develop. We compared rates of development of nevi from birth to 3 years of age in two cohorts of Caucasian children of similar ethnicity from the contrasting climates of Townsville, Australia [19° S; high levels of ambient UV radiation (4)], and Glasgow, U.K. [55° N; low levels of ambient UV radiation (5)]. The Australian cohort was recruited by approaching postpartum women at three maternity hospitals in Townsville during September and October 1994; 96.7% of the eligible mothers participated, resulting in a cohort of 115 babies of European ancestry. Scottish neonates were recruited from October 1993 through August 1994 by inviting postpartum women at the Queen Mother’s Hospital, Glasgow, to participate in a randomized intervention trial focused on sun avoidance in infancy (consent rate for parents at Queen Mother’s Hospital, Glasgow 97.4%). From the latter group, only control subjects (no intervention; n 157) were included in this study. The institutional review boards of the participating hospitals approved this study. The parents of all participants provided written, informed consent. In both countries, a standard international protocol was used to define and to count nevi of all sizes (6). Full-body nevus counts were performed on the Australian infants by an experienced observer (S. L. Harrison) (3) who was previously trained by dermatologists to recognize nevi (7). Nevi on the Scottish infants were counted by one of two experienced research nurses, and their counts were checked by a dermatologist (R. M. MacKie). Prior to the study, S. L. Harrison and R. M. MacKie reviewed numerous pigmented lesions together to standardize their nevus counting. Subjects were examined for nevi at birth (Australian cohort) or at 6 weeks of age (Scottish cohort) and within a month of their first, second, and third birthdays. Additional examinations of the Australian subjects were conducted at ages 6 and 18 months. Of the original 115 Australian infants, 88.7% and 77.4% were available for follow-up at ages 6 and 12 months, respectively. The retention rate for the Scottish cohort was higher, with 96.2% of the original cohort of 157 available for follow-up at 12 months of age. Retention for both cohorts is shown in Table 1. Only one of the 47 children lost from the Australian cohort over the 3-year period of follow-up withdrew by choice. The other 46 children were lost to follow-up because their families moved away. Of the 17 children lost from the Scottish cohort, 14 moved away or could not be contacted, one mother withdrew her consent, and follow-up of two subjects was not pursued for reasons unrelated to the study. Nevus counts were posit ively skewed. Consequently, we have presented the data as median nevus counts and interquartile ranges (IQRs). The chisquare and Wilcoxon rank sum (WRS) tests were used as appropriate (8). All P values are two-tailed. The proportion of Australian children with nevi increased rapidly in the first 2 years of life from 2.3% at birth to 65.2% (95% confidence interval [CI] 54.3%–75.0%) at 12 months and 100% (95% CI 95.3%–100.0%) at 24 months (Fig. 1). Corresponding proportions for the Scottish cohort were similar at age 6 weeks (3.2%; chi-square P for comparison with Australian children at birth .781), but they were consider-