Large congenital melanocytic nevi and the risk for the development of malignant melanoma. A prospective study.

BACKGROUND AND DESIGN: Patients with large congenital melanocytic nevi have been described to have an increased risk for the development of malignant melanoma (MM). Ninety-two patients with large congenital melanocytic nevi were followed up prospectively for the development of MM. Matched individuals from the general population served as control subjects.

RESULTS: Ninety-two patients (median age, 3 years) were followed up prospectively for an average of 5.4 years. In three patients (3%), MM developed in extracutaneous sites. The cumulative 5-year life-table risk for the development of MM was calculated to be 4.5% (95% confidence interval, 0% to 9.3%). In individuals in the general US population, matched for age, sex, and length of follow-up to the 92 study patients, 0.013 would be expected to develop MM. The standardized morbidity ratio (adjusted relative risk) was calculated to be 239, which was highly significant (P < .001).

CONCLUSIONS: Patients with large congenital melanocytic nevi are at a significantly increased risk for the development of MM and should be kept under continuous surveillance for the development of cutaneous as well as noncutaneous primary MM.