Supplementary Material for: Dermoscopy Improves the Diagnostic Accuracy of Melanomas Clinically Resembling Seborrheic Keratosis: Cross-Sectional Study of the Ability to Detect Seborrheic Keratosis-Like Melanomas by a Group of Dermatologists with Varying Degrees of Experience

<b><i>Background:</i></b> Malignant melanomas mimicking seborrheic keratosis (SK-like MMs) carry the risk of delayed diagnosis and inadequate treatment. The value of dermoscopy to improve the correct detection of these mimickers has not been previously studied. <b><i>Objective:</i></b> To evaluate the diagnostic accuracy of clinically SK-like MMs with and without dermoscopy. <b><i>Methods:</i></b> Clinical and dermoscopic images of histopathologically proven SK-like MMs (<i>n</i> = 134) intermingled with other melanomas and benign tumors were randomly presented to clinicians with different levels of experience, blinded to the diagnosis and goal of the study. Each participant classified each lesion as melanoma or benign tumor. The clinical and clinical-dermoscopic diagnostic accuracies were measured separately. <b><i>Results:</i></b> Overall, 54 participants with a mean clinical experience of 15.8 years (SD 11.8) evaluated 231 tumors. Almost 40% of SK-like melanomas were clinically misclassified as benign tumor. Dermoscopy improved diagnostic accuracy for all participants, independently of experience, from 60.9 to 68.1% (<i>p</i> < 0.001), mostly due to a significant increase in the sensitivity (clinical 61.9% vs. dermoscopic 74.5%) (<i>p</i> < 0.001). Dermoscopy did not significantly affect specificity among the experienced participants (≥6 years of experience) compared to clinical examination (61.1 vs. 59.6%, respectively); in contrast, dermoscopy was associated with a decrease in specificity compared to clinical diagnosis among novice participants (< 6 years) (45.6 vs. 61.1%, respectively; <i>p</i> = 0.02). <b><i>Conclusion:</i></b> Melanomas can be clinically indistinguishable from SKs despite being evaluated by expert dermatologists. Dermoscopy, even in nonexpert hands, significantly improves their recognition.