Recurrences after Mohs micrographic surgery (MMS) have been associated in the past with aggressive tumor type, large tumor size, and location within certain anatomic subunits. These factors are beyond the control of the treating physician and not subject to quality improvement efforts.

We sought to determine the relationship between slide quality and surgeon error with tumor recurrence after MMS.

This case-control study compared slide characteristics from 19 recurrent cancers previously treated using MMS with 95 nonrecurrent controls. The controls were randomly selected from a database of 6208 MMS cases from the University of California, Davis, from 2002 to 2009.

Significant factors for recurrences using χ² or Fisher exact tests included: tumor type, surgeon error, tissue drop out, dense inflammation, aggressive tumor subtype, and surgeries with 3 or more layers. After multivariate analysis with a stepwise regression model, factors that remained significant included surgeon error, tissue drop out, and aggressive tumor subtype.

The study involved only 2 surgeons and was from a single center. Not all recurrences were likely identified.

Surgeon errors resulting in persistent unexcised tumor were strongly associated with tumor recurrence. Tissue drop out and aggressive tumor subtype were also important factors. Two of these factors are within the control of the treating physician, and thus potentially improvable.