JAAD-D-21-01505R2, Correlation of Basal Cell Carcinoma Subtype with Histologically Confirmed Subclinical Extension During Mohs Micrographic Surgery: A Prospective Multi-Center Study
Description
Background: Traditionally “aggressive” histologic subtypes of basal cell carcinoma (BCC) are more likely to quantitatively exhibit subclinical extension (SCE), requiring more stages during Mohs micrographic surgery and therefore larger margins upon excision. However, the tendency for SCE has never been compared between histologic subtypes of BCC in a prospective manner. Objective: To prospectively correlate the histologic subtype of BCC with the likelihood of subclinical extension as defined by the number of MMS stages required to clear tumor. Methods: In a prospective, multi-center study involving 17 Mohs surgeons in 16 different practices across the United States, 1,686 cases of BCC undergoing MMS were collected. Patient demographics, tumor characteristics, number of MMS stages required for tumor clearance, and specific BCC subtypes noted on both index biopsy and final MMS stage were recorded. Results: Analysis of the average number of MMS stages for each histologic subtype required to clear tumor revealed two distinct degrees of SCE (P < 0.0001): high (higher than average) risk of SCE (1.9 stages, 1.0 SD), and low (lower than average) risk of SCE (1.6 stages, 0.9 SD). Subtypes of BCC within the high category were morpheaform (2.1), infiltrative (1.9), metatypical (1.9), mixed (1.8), and superficial (1.8). The low category included BCC subtypes of basosquamous (1.6), micronodular (1.6), nodular (1.6), and unspecified (1.5). Three hundred twenty-four cases (22.0%) manifested histologic subtype (HS) drift, or a change in subtype from index biopsy to final MMS stage. Superficial BCC was the only subtype that showed an increase in prevalence from index biopsy to final MMS stage (16.0% to 25.8%, P < 0.0002). Limitations: Histologic subtypes from index biopsy may not be representative of all histologic subtypes present, resulting in sampling bias. Conclusion: Subclinical extension of superficial BCC was as likely as SCE of BCC subtypes which are considered “aggressive” and are deemed “appropriate” for MMS by the AUC. Our study also found that when HS drift occurs, the most likely subtype to extend subclinically is superficial BCC.