Nevus-associated melanomas (NAM) are thinner, more likely to be found on the torso, and more often occur in younger patients compared with de novo melanomas (DNM), according to a study in the Journal of the European Academy of Dermatology and Venereology.

Researchers compared the clinical and dermoscopic features of patients with NAM and DNM from melanomas that were biopsied at a large tertiary cancer center from 2004 to 2019 in this cross-sectional study. The lesions were categorized into 4 groups: in situ NAM, invasive NAM, in situ DNM, and invasive DNM.

The NAM group included 138 patients (mean age, 60.1 years; 2:1 male:female ratio; 160 lesions [86 in situ, 74 invasive]), and the DNM group included 196 patients (mean age, 65.2 years; 3:2 male:female ratio; 218 lesions [109 in situ, 109 invasive]).


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NAM, compared with DNM, were associated with younger age, greater likelihood of being present on the torso (73% of lesions vs 43% of lesions, respectively), and thinner Breslow thickness (0.48 mm vs 0.72 mm, respectively). NAM were also more likely to be invasive compared with DNM (46% vs 28%, respectively).

NAM were 2.5 times more likely than DNM to have a negative pigment network. Regarding in situ melanomas, NAM were 2.1 times more likely to have a dermoscopic area without definable structures and 2 times more likely to have tan structureless areas compared with DNM. All other dermoscopic characteristics were not significantly different between NAM and DNM. The results were similar after a subgroup analysis was performed that excluded all invasive melanomas that were more than 1 mm in Breslow depth.

Patients with invasive melanomas more frequently presented with scarlike depigmentation and shiny white structures, compared with those who had in situ melanomas. Invasive DNM were more frequently characterized by areas without definable structures than in situ DNM, a feature that was similar in invasive and in situ NAM. In addition, invasive NAM were more likely to feature peppering than in situ NAM, and the difference in peppering between invasive and in situ DNM was not statistically significant.

The mean Breslow depth of invasive melanomas was 0.62 mm and was deeper on average in lesions that had streaks (1.1 mm vs 0.59 mm), blotches (1.14 mm vs 0.54 mm), and shiny white structures (1.3 mm vs 0.54 mm).

The study was limited by its retrospective nature and by previous images not being available to evaluate whether a nevus had been present before the appearance of a melanoma in most cases. Also, the reliance on pathology reports may have reduced the accuracy of the findings.

“Even though nevus components were not identified dermoscopically in the current series, negative pigment network, areas without definable structures, and tan structureless areas are dermoscopic clues for NAM, the former of which is consistent with prior research,” the study authors commented.

Reference

Reiter O, Kurtansky N, Nanda JK, et al. The differences in clinical and dermoscopic features between in situ and invasive nevus-associated melanomas and de novo melanomas. J Eur Acad Dermatol Venereol. Published online January 28, 2021. doi:10.1111/jdv.17133