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.
**背景/目的：** 躯干部位黑素细胞性皮损的诊断具有挑战性，因为良性痣常表现出较高的非典型特征频率，导致不必要的切除率较高。本研究旨在确定躯干部位皮肤黑色素瘤可靠的皮肤镜预测因子，并评估一项新的诊断标准：皮损相对于朗格氏皮肤张力线的方向。**方法：** 我们对从躯干切除的321例黑素细胞性皮损（227例痣和94例黑色素瘤）进行了回顾性分析。系统性地评估了皮肤镜特征。采用卡方检验以及经年龄和性别调整的多变量逻辑回归分析来计算比值比（OR），并确定恶性的独立预测因子。还对"关键"与"非关键"解剖部位进行了亚组分析。**结果：** 不遵循朗格氏线方向是黑色素瘤最强的预测因子（OR 5.55，95% CI 3.22–9.81；p < 0.001）。其他显著的预测因子包括蓝白幕（OR 5.09）和多形性血管（OR 4.06）。值得注意的是，70%的黑色素瘤与朗格氏线方向不一致，而72%的痣则与之相符。在本队列中，诸如瘢痕样退行性变等经典特征并非统计学上显著的预测因子。在亚组分析中，颜色不对称仅在非关键部位是黑色素瘤的显著预测因子（交互作用p值 = 0.026）。**结论：** 黑素细胞性皮损相对于朗格氏线的方向是躯干部位黑色素瘤一个强大且独立的预测因子。这一简单的形态学特征可能反映了良恶性皮损生长模式的差异，可作为一项额外的临床线索，在此具有挑战性的解剖部位辅助决策并提高诊断准确性。
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