Comparative dermoscopy assessment of nevus-associated versus de novo in situ melanoma

Background: Dermoscopic features differentiating in situ nevus-associated melanoma (NAM) versus in situ de novo melanoma (DNM) are inconclusive. Objectives: The aim of the study was to investigate the dermoscopic features associated with in situ NAM versus DNM. Materials & methods: This was a retrospective observational study. All consecutive in situ melanomas diagnosed in adult patients were retrieved and stratified as NAM vs DNM, and clinical and dermoscopic data were compared between the two. Results: A total of 183 patients with in situ melanoma were collected, of whom 98 (54%) were male with a mean age of 64±14 years. For 129 patients, standardized dermoscopic images were collected (51 for NAM and 78 for de novo MM). The most common dermoscopic features were an atypical pigment network (85%), atypical globules (63%) and regression (42%). No significant differences were found except for regression, which was detected in 54.9% NAM vs 33.3% DNM (p=0.016). Multivariate logistic regression confirmed the association between dermoscopic regression and NAM (OR=2.34, 95% CI: 1.15-4.91). Conclusion: Currently, the use of dermoscopy to determine whether a melanoma is associated with a nevus is unreliable, however, the presence of regression adjacent to atypical lesions may raise suspicion of in situ NAM.