Mohs Micrographic Surgery Dermatopathology Concordance in Canada: A Single-Institution Experience

Background: Mohs micrographic surgery (MMS) is a surgical modality that achieves high cure rates of nonmelanoma skin cancers but is dependent on accurate histologic examination of surgical margins. Therefore, quality assurance is essential to ongoing assessment of histological margins. Objectives: To prospectively determine the concordance rate between a Mohs surgeon (MS) and dermatopathologist (DP) with respect to tumour status (ie, present or absent) and tumour type. Secondary end points were to determine the relationship between discordant interpretations and slide quality and to assess the feasibility of using an electronic webform for data collection. Methods: Ten percent (10%) of the planned MMS cases between January 2015 and March 2016 were randomly selected by a histotechnologist at the start of each month. The MS and DP were blinded to the chosen cases, and slides were reviewed independently at the beginning of the following month. Data were collected using an online webform. A blinded third party determined if there were discrepancies in interpretation, and any discordant slides were reviewed together and a consensus was reached. Results: A total of 270 slides from 54 total cases were reviewed. The overall tumour status concordance rate was 93.6%. Cohen's kappa was 0.86. Tumour type concordance was 98.9%. No discrepancy required a change in patient care. All discrepant slides were from cases that required multiple stages. Conclusions: This is the first study looking at MS-DP concordance in Canada, and our findings support the MS acting as his or her own pathologist.