Factors to Predict 13 or More Sections in Mohs Micrographic Surgery

Studies on factors that predict the number of stages in Mohs micrographic surgery (MMS) have been published previously. To date, no studies have analysed the predictors for the number of sections during MMS.

A retrospective case-control study of patients treated for keratinocyte cancer (KC) between 2013 and 2017 was conducted to identify predictive factors for 13 or more MMS sections. Patient, tumour, management and practitioner-related factors were analysed with univariate logistic regression and a multivariate predictive model. Surface area for tumours and defects was studied in cases and controls as a secondary outcome.

Out of 10,132 tumours, a total of 195 cases representing 1.9% of all MMS procedures for the study period required more than 13 MMS sections. A control group with 213 tumours was also randomly selected. Largest preoperative tumour diameter, mixed histology, tumour recurrence and age were significant predictors for 13 or more MMS sections in a multivariate model (AUC 88.4%, sensitivity 77.2% and specificity 87.0%). Significantly larger defects were also found in our cases compared to the control group (median tumour to defect ratio 3.94 vs. 2.43; p < 0.0001).

Identifying factors that predict 13 or more sections prior to surgery could assist the Mohs practitioner in informing patients and allocating time and resources accordingly.