Melanoma Clues Beyond Dermoscopic Patterns: Lesion Orientation to Langer's Lines as a Predictor on the Trunk

Background/Objectives: The diagnosis of melanocytic lesions on the trunk is challenging due to a high frequency of atypical features in benign nevi, leading to a high rate of unnecessary excisions. This study aimed to identify robust dermoscopic predictors of cutaneous melanoma on the trunk and to evaluate a novel diagnostic criterion: the orientation of lesions relative to Langer’s skin tension lines. Methods: We conducted a retrospective analysis of 321 melanocytic lesions (227 nevi and 94 melanomas) excised from the trunk. Dermoscopic features were systematically evaluated. A chi-square test and an age- and sex-adjusted multivariate logistic regression were performed to calculate odds ratios (OR) and identify independent predictors of malignancy. A subgroup analysis was also conducted on “critical” versus “non-critical” anatomical sites. Results: Non-adherence to Langer’s lines was the most powerful predictor of melanoma (OR 5.55, 95% CI 3.22–9.81; p < 0.001). Other significant predictors included blue-white veil (OR 5.09) and polymorphous vessels (OR 4.06). Notably, 70% of melanomas did not align with Langer’s lines, whereas 72% of nevi did. Classic features such as scar-like regression were not statistically significant predictors in this cohort. In the subgroup analysis, color asymmetry was a significant predictor of melanoma only in non-critical sites (p for interaction = 0.026). Conclusions: The orientation of a melanocytic lesion relative to Langer’s lines is a powerful and independent predictor of melanoma on the trunk. This simple morphological feature, which may reflect differences in growth patterns between malignant and benign lesions, could serve as an additional clinical cue to support decision-making and improve diagnostic accuracy in this challenging anatomical location.