Cutaneous melanoma histologically associated with a nevus and melanoma de novo have a different profile of risk: Results from a case-control study

Background: Histopathologic association between melanocytic nevus and melan oma has been reported in approximately 10% to more than 50% of melanoma cas es. Whether melanomas in contiguity with a nevus have a different natural h istory and pathogenesis from melanomas without a nevus is still to be deter mined. Objective: The present study was undertaken to clarify whether melanocytic nevus-associated melanomas (MN[+]) have a different risk factor profile fro m cases without histopathologic evidence of melanocytic nevus association ( MN[-]). Methods: The study population consisted of 131 invasive melanoma cases with a thickness of 4.00 mm or less and 174 control cases without melanomas. Th e whole series was evaluated for the following risk factors: phenotypic tra its; the number of common, atypical, and congenital nevus-like nevi; and fr eckling and history of sunburns. Melanoma cases were revised for the presen ce of associated melanocytic nevi. The analysis of risk factors was perform ed by a case-control approach comparing cases, classified by histologic ass ociation with nevus, to the group of controls. Possible differences in risk factor distribution between MN(+) cases and MN(-) cases were evaluated wit h a polychotomous logistic regression model and a likelihood ratio test for heterogeneity. Results: Histopathologic association between melanocytic nevus and melanoma was found in 27 cases (20.6%). Phenotypic traits were shown to be more pow erful predictors of risk for MN(-) than for MN(+) cases (blond/red hair; od ds ratio, 7.4 and 1.2, respectively; likelihood ratio test for heterogeneit y, 4.13; P < .05). Conversely, history of frequent sunburn was a risk facto r only in MN(+) cases (more than 5 sunburns; odds ratio, 6.7; 95% confidenc e interval, 1.3-33.7), but not in MN(-) cases (odds ratio, 1.2; 95% confide nce interval, 0.3-4.0; likelihood ratio test for heterogeneity, 4.2; P < .0 5). Where melanocytic nevi are concerned, an increased number of common nev i was a predictor of melanoma risk in both MN(+) and MN(-) cases, but with a different magnitude of risk, higher for MN(+) cases (number of common nev i, 10-30; odds ratio, 14.4 and 4.7, respectively; likelihood ratio test for heterogeneity, 3.7; P = .055). Conclusion: This study showed that, although MN(+) and MN(-) melanomas shar e many risk factors, there is a different strength of association between t he 2 groups. The effect of a history of sunburn as a predictor of risk was found only for nevus-associated melanomas, suggesting a possible role of su nburns in the neoplastic transformation of nevi.