Risk factors for melanoma incidence in prospective follow-up. The importance of atypical (dysplastic) nevi.

BACKGROUND AND DESIGN

Assessment of melanoma risk factors can help identify individuals at greatest risk for melanoma. Previous studies were retrospective case-control or prospective without control groups. A prospective group of 3889 employees without previous melanoma or family history of multiple melanoma at the Lawrence Livermore (Calif) National Laboratory were examined as part of a melanoma screening program. Their subsequent incidence of melanoma in relationship to potential melanoma risk factors, which were recorded at the first examination, was determined.

RESULTS

Nine invasive melanomas developed after initial examination among the studied population over an 8-year period with an average follow-up of 5 years. The presence of an easily recognized pattern of definite clinically atypical (dysplastic) nevi was present in 7% of employees and was associated with a cumulative melanoma risk of 1.9%. It was the strongest risk factor, with a relative risk of 47 compared with the 0.04% cumulative melanoma risk in the 64% of employees with no atypical (dysplastic) moles (chi 2 for equal risk, P = 7 x 10(-8). Significant, but less marked associations with melanoma risk were found for the total number of moles and for a history of many moles in other family members, with a maximal relative risk of 11.6 and 10.4, respectively.

CONCLUSION

A small subgroup of the population with easily recognizable definite atypical (dysplastic) nevi have a marked increased risk of melanoma. Smaller significant melanoma risks were found for a total number of moles and a family history of many moles.