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Few medical procedures have the mystique that surrounds Mohs micrographic surgery (MMS). While most physicians whose work involves treating skin cancer understand it in principle, many are less aware of what is wholly involved or how it is performed. Some patients may have also heard of it and, after conducting a little research, concluded that it is what they want for their skin cancer as the term is practically synonymous with the highest chance of cure. They can view MMS as a silver bullet, a mysterious yet infallible solution to their condition; one minor procedure and, like magic, their lesion will be fixed. While there is a reason for this optimism, the physician must rely on deeper knowledge and careful judgment.

MMS has enjoyed enormous success as a procedure, probably more so than any other form of margin control surgery (MCS). Training programs and quality assurance programs help ensure standardization and quality. Societies with annual meetings encourage collegiality and innovation. Specialist technicians have also developed societies, training programs, and continued education. With these developments, its popularity has increased around the world and its use has diversified to treat an ever-wider range of tumors and clinical situations.


There seems to be a variety of definitions for what MMS is. It has been defined as a procedure performed by a dermatologist who acts as both the surgeon and pathologist. The dermatologist performs the surgery to remove the tumor, examines the margins intraoperatively with horizontal frozen sections, maps positive margins and re-excises the positive areas until the margins are clear, and then typically performs the reconstruction. But there is considerable variability internationally. For example, sometimes the surgeon is not a dermatologist, sometimes a pathologist is involved in interpreting the slides, sometimes the reconstruction is performed by a reconstructive surgeon, and sometimes the Mohs surgeon is only involved in the interpretation of the histopathology slides. The term has been stretched further still: Some apply this term to any procedure which involves examination of 100% of the margins intraoperatively regardless of the pathology processing used or the specialists involved. Further confusion is added by the use of the term “slow Mohs,” which usually means examination of the entire margin with formalin-fixed paraffin-embedding processing.


The suitability for MMS was formalized in the United States with the appropriate use criteria (AUC) publication produced in 2012 by the American Academy of Dermatology (AAD) in collaboration with the American College of Mohs Surgery, the American Society for Dermatologic Surgery, and the American Society for Mohs Surgery. Clinical scenarios were developed following consultation with 70 experts and then a panel of raters scored the appropriateness of MMS for each scenario. The panel consisted of 17 dermatologists, of which eight were practicing MMS surgeons. Similar guidelines have been developed by equivalent bodies in other countries and territories.


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