Background: Melanocytic nevi (MN) are markers of melanoma risk, but their potential role as precursors of cutaneous malignant melanoma (CMM) is still controversial.
Objective: The overall and site-specific relative risk (RR) of developing CMM was evaluated according to site-specific MN counts.
Methods: MN prevalence by anatomic site and by age was compared in 200 CMM patients and in 200 nonmelanoma control subjects; RRs were calculated.
Results: In CMM patients both MN and CMM were mainly found on the legs in women and on the posterior trunk in men, whereas in the control subjects most MN were found on the arms. MN counts on the trunk in men and on the legs in women were best predictors of the overall CMM risk (RR: 33-fold and 15-fold, respectively, for greater than 20 vs up to 4 MN). For both genders combined, the RR for CMM developing on the trunk and legs (predominant CMM locations) was best predicted by MN counts in the respective body region (RR: 24-fold and 27-fold, respectively). MN prevalence peaked in the fourth to fifth decade of life and most CMM were diagnosed during the fifth and sixth decades.
Conclusion: The site-specificity of melanoma risk found for high MN counts on the trunk and the legs and the close similarities in age distribution suggest that the role of MN as direct precursors of CMM has been underestimated and exceeds the number of histologically evident MN associated with CMM.