Unusual dermoscopic patterns of basal cell carcinoma mimicking melanoma

Background Basal cell carcinoma can simulate melanoma and specific dermoscopic criteria have not yet been defined in a large cohort. Objective To identify dermoscopic "trump" characteristics for differential diagnosis, identify cluster groups and assess the clinical impact of this study's findings. Methods Retrospective, multicentric comparative study of atypical, non-facial basal cell carcinoma (>= 1 seven-point checklist criteria) and melanoma (with at least one BCC criteria) at dermoscopy. Observed dermoscopic features were used to develop a proposed score. Lesion clusters were defined with hierarchical analysis. Clinical impact was assessed with a blinded reader study following this study's results. Results A total of 146 basal cell carcinoma and 76 melanoma were included. Atypical vascular pattern was common to most lesions (74.5%). Twelve trump features were included in the proposed score (sensitivity 94.1% and specificity 79.5%). Cluster analysis identified 3 basal cell carcinoma and 3 melanoma clusters. Findings improved overall diagnostic accuracy and confidence (26.8% and 13.8%, respectively; p < 0.001). Conclusions These findings support the notion that atypical vascular pattern should be considered a shared feature of both melanoma and atypical basal cell carcinoma. Our proposed score improves diagnostic accuracy and confidence. Absence of pigmented features was associated with lower diagnostic accuracy and confidence.