Concordance in Distinguishing Actinic Keratosis from Squamous Cell Carcinoma in Situ on Mohs Histological Frozen Sections.

Background: Mohs surgeons routinely encounter squamous cell carcinoma at surgical margins and often base the decision to take another layer on the severity of atypia observed. Currently, no criteria exists for distinguishing borderline histological patterns that could be interpreted differently as actinic keratosis (AK), squamous cell carcinoma in situ (SCCIS), or AK with focal SCCIS.

Objective: To assess interrater concordance amongst Mohs surgeons in distinguishing AK from SCCIS when evaluating Mohs frozen sections.

Methods: Seventeen slides were selected and converted into digitally formatted cases. They were compiled into an electronic survey and distributed to the American College of Mohs Surgery.

Results: Overall κ was 0.26 corresponding to weak agreement between raters compared to the standard, with κ of 0.34 for AK and 0.37 for SCCIS.

Conclusion: There exists notable variability among Mohs surgeons who interpret the spectrum of in situ carcinoma differently. Ongoing learning and consensus building among Mohs surgeons and trainees can aid in quality patient care, even if there may not be agreement on every case. J Drugs Dermatol. 2023;22(2):199-194. doi:10.36849/JDD.7084.