Misclassification of Aggressive Basal Cell Carcinoma Subtypes and Implications for Management.

Background: Management of basal cell carcinoma (BCC) varies by histopathologic subtype; however, biopsies may inadequately characterize them as nonaggressive, risking potential suboptimal treatment.

Objective: To characterize the rate of undetected aggressive BCC subtypes by size, location, and histopathology type. Materials and

Methods: Retrospective cohort study of 928 BCCs treated with Mohs Micrographic Surgery (MMS) at a tertiary academic institution from 2015 to 2017, comparing patient and tumor characteristics and histopathologic subtype on biopsy versus Mohs.

Results: Among the 825 BCCs with known subtypes on biopsy, 68% (561/825) were classified as nonaggressive, 28% (159/561) of which were subsequently found to have aggressive subtypes on MMS. Aggressive features were more often underrepresented in biopsy samples taken from Area H compared with Area M/L (odd ratio [OR] 2.65, 95% confidence interval [CI] 1.73-4.08, p < .001) or those with nodular subtypes (OR 2.19, CI 1.08-4.45, p = .03). Of concern, these unsuspected aggressive BCCs required more Mohs stages for clearance (mean 2.37, SD 0.72, p < .001) compared with BCCs that remained nonaggressive on both biopsy and Mohs (mean 1.50, SD 0.75).

Conclusion: Given the high percentage of BCCs with unsuspected aggressive subtypes, higher clinical suspicion for undiagnosed high-risk BCCs should be given to nodular BCCs and to BCCs on Area H.