Concordance of basal cell carcinoma subtyping at biopsy vs. excision, and the implications for clinical approach: a multicenter cohort study

The purpose of this retrospective multicenter cohort study of consecutive cases at 3 academic centers was to determine whether preoperative biopsies of BCC detect all subtypes present. Included were adult patients with biopsy diagnosis of primary BCC and subsequent detection of tumor in Mohs specimens. Two dermatologists recorded subtypes in each biopsy report, and two others, subtypes detected in frozen section glass slides associated with corresponding Mohs excisions. Among 827 biopsies, mixed histology was identified in 57%, but reported in 18%. A median of 1 subtype was observed in biopsies (IQR: 1-1) and 2 in excisions (IQR: 1-2). Ninety-nine percent of cases showed concordance between excision and biopsy, with 31% having identical subtypes. Biopsy and excision histology were equally clinically aggressive in 69%, excision more aggressive in 25%, and biopsy in 6%. Biopsies of BCC can fail to detect all histologic subtypes despite impeccable histologic sectioning and assessment by a dermatopathologist due to the small amount of sampled tissue. Importantly, surgeons performing definitive excisions should realize it is unrealistic to expect all present BCC subtypes to be detected in minute biopsy specimens, and should be prepared to encounter and adequately treat additional aggressive subtypes.