Minimizing the dermatoscopic morphologic overlap between basal and squamous cell carcinoma: a retrospective analysis of initially misclassified tumours

Background: Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) have well-established dermatoscopic criteria that make them relatively easy to recognize on a clinical basis. However, even with the addition of dermatoscopy, a morphologic overlap between the two tumours does exist. Objectives: To analyse the dermatoscopic morphology of clinically and dermatoscopically misclassified BCCs and SCCs, to identify factors causing the erroneous clinical interpretation and, therefore, minimize the morphologic overlap between BCC and SCC. Methods: Retrospective study including histopathologically diagnosed BCCs or SCCs that had been clinically inversely diagnosed. Their dermatoscopic images were blindly evaluated for the presence of predefined criteria. Descriptive statistics were performed and univariate and multivariate predictors were calculated. Results: A total of 68 cases were included, 41 of which were BCCs and 27 SCCs. Most tumours in both groups were non-pigmented, ulcerated and displayed a polymorphous vascular pattern. The presence of erosions was positively associated to BCC (5.2-fold higher odds, P = 0.05), whereas scales/keratin masses were positively associated to SCC (3.7-fold higher odds, P = 0.07), although marginally not statistically significant. Conclusions: Clinically misclassified BCCs and SCCs are usually non-pigmented ulcerated tumours. Erosions and keratin masses/scales are more robust criteria as compared to vascular structures for the differential diagnosis between BCC and SCC.