Dermoscopy in Merkel Cell Carcinoma—A Multicenter Retrospective Study of the International Dermoscopy Society

Background: Merkel cell carcinoma (MCC) is a rare neuroendocrine tumor that usually presents as a pink nodule on sun-exposed skin in elderly patients. This study aimed to investigate the dermoscopic patterns of MCC and identify predictors that may help distinguish it from other benign or malignant tumors often included in its differential diagnosis. Methods: This was a study announced via an online call on the International Dermoscopy Society website where we collected macroscopic and dermoscopic images of MCC and other tumors with similar clinical morphology that served as controls. Sixteen experts were asked to assess the images for the presence of preselected dermoscopic features. Univariable feature analysis, multivariable logistic regression analysis, and interrater reliability assessment were performed. Results: In total, 402 cases were collected: 134 MCCs and 268 controls. Three hundred and ninety six images were included in the analysis after the exclusion of poor-quality photographs. Pink color was the most common feature in MCC (92.4%, 95% confidence interval [CI]: 1.17–5.7), followed by white color (58%, 95% CI: 0.62–1.51) and linear irregular vessels (43.5%, 95% CI: 0.61–1.47). Scale on the surface was documented in 33.6% of MCCs compared to 23.4% of controls (95% CI: 1.01–2.69). Multivariable logistic regression analysis identified two positive predictors of MCC, namely pink color and scale, and three negative predictors, namely ulceration, brown, and blue-gray pigmentation. Conclusion: MCC might mimic other benign or malignant lesions. In nonpigmented tumors dermoscopically characterized by pink color and scales, MCC should be prioritized among the differentials.