Mohs Margins in Stage-1-Positive Basal Cell Carcinoma Are Often Histologically Shallow Irrespective of Biopsy...

Presurgical biopsy subtype guides basal cell carcinoma (BCC) risk stratification, but how well it predicts histopathology at the Mohs margin is unclear. Noninvasive imaging with reflectance confocal microscopy (RCM), line-field confocal optical coherence tomography (LC-OCT), and optical coherence tomography (OCT) may detect margin-localized tumor within imaging depth.

The aim of this study was to quantify low-risk-only histopathology at stage-1 positive Mohs margins by biopsy subtype and estimate histology-based amenability to RCM, LC-OCT, and OCT.

This retrospective analysis included 108 primary BCCs treated with Mohs micrographic surgery from January 2021 through November 2022. Cases with first-stage margin positivity and retrievable Mohs slides were reviewed. Potential imaging amenability was estimated as a histologic surrogate, using the depth from the granular layer to the tumor top with modality-specific thresholds of RCM ≤ 150 μm, LC-OCT ≤ 300 μm, and OCT ≤ 720 μm.

Overall, 63.9% of cases showed low-risk-only histopathology at the stage-1 positive margin, whereas only 33.3% were classified as low-risk-only on biopsy. Histology-based imaging amenability was 55.6% for RCM, 65.7% for LC-OCT, and 76.9% for OCT. Among high-risk biopsy cases, estimated amenability remained substantial: 51.4%, 63.9%, and 75%, respectively.

Biopsy subtype underpredicted the low-risk-only Mohs margin phenotype. Using histologic depth as a surrogate, many first-stage margin breaches were shallow enough to fall within modality-specific depth thresholds, including in high-risk biopsy tumors. As no in vivo imaging was performed, these findings estimate potential detectability and support feasibility and trial design rather than demonstrating imaging performance.