THE RISK OF MELANOMA IN PATIENTS WITH CONGENITAL NEVI - A COHORT STUDY

Background: Giant congenital nevi are associated with a greatly increased risk of melanoma, but this has not been quantified. Smaller congenital nevi are believed by some authors to be associated with increased risk, but this is uncertain and needs to be clarified. Objective: Our purpose was to analyze cause-specific mortality and cancer incidence risks in patients with congenital nevi according to size of the nevi. Methods: We followed up 265 patients with congenital nevi first treated at the Hospital for Sick Children or at St. John's Hospital in London during 1950 to 1984 for mortality to mid-1993 and for cancer incidence from 1971 to 1989. Mortality and cancer incidence rates in the cohort were compared with expectations from national mortality and cancer incidence rates by sex, age, and calendar period. Results: Among the 33 patients with a congenital nevus covering at least 5% of the body area, two melanomas occurred during follow-up; both were fatal. The relative risk of melanoma mortality in these patients was 1046 (95% confidence interval, 127 to 3779). In the remaining 232 patients, 68 of whom had a nevus covering 1% to 4% of the body, and 164 with nevi smaller than 1% of body area, no melanomas occurred (0.18 melanoma deaths expected). The difference in melanoma mortality risk between the group with a nevus covering at least 5% of the body and the group with smaller nevi was significant (p < 0.05). There was not a significantly increased risk of nonmelanoma mortality or of nonmelanoma cancer incidence overall in the cohort, although two lymphohematopoietic malignancies occurred. Conclusion: The data show the large risk of melanoma in patients with nevi covering more than 5% of the body surface area. The results do not support the hypothesis of greatly increased risk in persons with congenital nevi smaller than this, but because the confidence intervals of the result were wide, the data are compatible with a sizable risk. Much larger studies than those that have so far been undertaken, or combined analysis of data from several studies, are needed to quantify more precisely the risk of melanoma in relation to size of nevi and to determine the appropriate clinical management of these lesions.