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 id entify individuals at greatest risk for melanoma. Previous studies wer e retrospective case-control or prospective without control groups. A prospective group of 3889 employees without previous melanoma or famil y history of multiple melanoma at the Lawrence Livermore (Calif) Natio nal Laboratory were examined as part of a melanoma screening program. Their subsequent incidence of melanoma in relationship to potential me lanoma 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 pa ttern 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 co mpared 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 wer e 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 ea sily recognizable definite atypical (dysplastic) nevi have a marked in creased risk of melanoma. Smaller significant melanoma risks were foun d for a total number of moles and a family history of many moles.