A multicenter study of nevus-associated melanoma versus de novo melanoma, tumor thickness and body site differences.

Background Whether melanoma in histological contiguity with a nevus (nevus-associated melanoma, NAM) is distinctly different from melanoma arising de novo remains unclear. Objectives To determine whether the characteristics of de novo melanoma differ from NAM and are not due to nevus obliteration in thicker tumors. Methods A multicenter retrospective study of de novo melanoma and NAM in 7 referral centers in Europe, Australia and the USA, between 2006 and 2015. Results In a total of 9,474 localized melanomas, de novo melanoma compared to NAM was associated with thicker tumors and body-site differences. In the subset of T1 melanomas (n=5,307), similar body-site differences were found in multivariate analysis by body site: de novo melanoma compared to NAM, was more likely to affect older individuals (≥70 years) when located on the head/neck (OR: 4.65, 95% CI: 2.55-8.46), on the trunk (OR: 1.82, 95% CI:1.40-2.36), or on the upper extremity (OR: 1.69, 95% CI: 1.14-2.50), to affect females when located on the lower extremities (OR:1.36, 95% CI: 1.03-1.80), to be of the NM subtype (OR: 2.23, 95% CI: 1.14-4.35) when located on the trunk, while it was less likely to have regression present. Conclusions Clinicopathological and body site differences between de novo melanoma and NAM support divergent pathways of development. These differences were also found in thin melanomas, suggesting that de novo melanomas are different from NAM and their differences are not due to the obliteration of nevus remnants in thicker tumors.