Laboratory errors leading to nonmelanoma skin cancer recurrence after Mohs micrographic surgery

Compared with standard surgical excision, Mohs micrographic surgery (MMS) provides superior cure rates for nonmelanoma skin cancer (NMSC). Although cure rates of NMSC approach 99% with MMS, local recurrences occasionally occur.

The authors sought to identify histological features during frozen section examination that were associated with local recurrence of NMSC after MMS.

A retrospective chart review was performed of patients undergoing a second MMS procedure to treat locally recurrent NMSC over a 20-month period. Histological slides were reviewed to assess for possible causes of local recurrence.

Of 3,169 NMSCs treated, 22 were locally recurrent. Possible causes of recurrence identified after MMS included dense inflammation in the final margin at sites affected by tumor in prior slides (27%), visible remaining tumor (23%), missing epidermal or dermal tissue (23%), and actinic keratosis (4%). One recurrence was possibly explained by incorrect mapping. No abnormality could be detected in 18% of cases. Possible limitations include the small sample size, retrospective design, and the possibility that some patients may have been lost to follow-up.

Local recurrences after MMS are extremely rare. When recurrences do occur, they can be attributed to errors in histological interpretation or tumor mapping.