Unusual Dermoscopic Patterns of Basal Cell Carcinoma Mimicking Melanoma

Abstract: 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). Limitations: Retrospective design and proposed score unvalidated. Conclusions: Atypical vascular pattern should no longer be considered a melanoma associated feature only. Our proposed score improves diagnostic accuracy and confidence. Absence of pigmented features were associated with lower diagnostic accuracy and confidence. Conclusions: Our proposed score improves diagnostic accuracy and confidence. Absence of pigmented features were associated with lower diagnostic accuracy and confidence. Legends: Figure S1. (a-c) MM; (b-d) BCC. Dermoscopic features: white-red structureless areas (white star), atypical vascular pattern (black circle), multiple blue-gray globules (black triangle), regression structures (black rectangle), maple leaf-like areas (white triangle). MM, malignant melanoma; BCC, basal cell carcinoma. Figure S2. BCC. Lesions representative of the hypo/amelanotic-MM like cluster: (a-c-e) clinical images;(b-d-f) white-red structureless areas (asterisk), (b-d-f) atypical vascular pattern (black circle), (b-d-f) superficial (short) fine telangiectasia (triangle), (b-d-f) ulceration (rectangle), (b-d-f) some arborizing vessels (arrows). MM, malignant melanoma; BCC, basal cell carcinoma. Figure S3. BCC. Lesions representative of the mixed cluster: (a-c-e) clinical images; (b-f) superficial (short) fine telangiectasia (black triangle), (b-d-f) multiple blue-gray globules (asterisk), (b-d) atypical vascular pattern (white triangle), (b-f) white-red structureless areas (rectangle), (f) irregular dots/globules (arrows), (f) white streaks (circle). BCC, basal cell carcinoma. Table S1. Dermoscopic features classified according to common associations in literature with malignant melanoma (MM) and/or basal cell carcinoma (BCC) diagnoses Table S2. Demographic and clinical details for the included patients.