Final Musings on Mohs Surgery

What you need to know before you undergo Mohs surgery

“Mohs, which stresses taking thin margins, has no place in treating melanoma.”

For thirty-five years I have dealt with the issue of Mohs surgery for removal of common skin cancers- basal cell and squamous cell cancers. This post will be my final word on the subject. I hope it will help readers who are diagnosed with skin cancer and wonder how best to manage this.

Mohs surgery was developed by Dr. Frederic Mohs while he was still a medical student in the 1930’s. It has barely changed in the decades since. Now called Mohs Micrographic Surgery (MMS) it remains the exclusive purview of Dermatology. The laudable goal of MMS is to remove skin cancers with clear margins and as little normal skin as possible. It is typically used on facial cancers although it can be performed anywhere, and is always done in an office setting. The skin cancer is removed under straight local anesthesia, the patient bandaged and sent out to a waiting room, and the surgeon examines the specimen to assess the margins. If they are clear, the patient is brought back to have the site sutured or otherwise closed in some fashion. If the margins are not clear, the patient is brought back, more skin removed, and the process repeats until clear margins are obtained. Each excision stage takes around 45 minutes or so. Because the MMS surgeon cuts right along the margin of the cancer, positive margins are more common than not. With MMS, the average skin cancer requires 1.7 excisions, which means that many require two or more excisions for clear margins. I have seen patients who had as many as 8 excisions over the course of an entire day before arriving at my office for reconstruction. I believe this is highly inappropriate use of MMS.

The dermatologist may close the wound themselves, but if it is in a critical area, such as around the eye, or unusually large, the patient may be referred to a plastic surgeon for reconstruction. In some cases, the wound will be left open for days. In some cases, the wound is left to heal on its own and the cosmetic result may be less than ideal.

In contrast to MMS, traditional excision (TE) of routine skin cancers by a plastic surgeon is done by simply excising them with a small, 1-2 mm, margin of skin beyond any visible cancer. This is sufficient to fully excise the cancer with clear margins in over 95% of patients. The margins can be evaluated immediately by freezing and examining the specimen, and the reconstruction can proceed immediately, whether by simple suture closure or a small skin graft or flap. The wound is never left open. In the vast majority of cases, this is a simple office procedure using local anesthesia, and takes from 45-60 minutes from start to finish. The advantages are many. Plastic surgeons typically operate in facilities that permit the use of intravenous sedation, which can allay a lot of patient anxiety when working on the face. Dermatologists usually do not have this option. The patient is never left with an open wound to be closed by a plastic surgeon later. The cost for TE to patients is often significantly less than MMS. Cure rates are comparable, but in one study MMS was more likely to give false positive margins, which may explain why MMS typically requires more exisions and often results in unusually large wounds.

In some areas, MMS surgeons and plastic surgeons work closely together according to my daughter, who is a dermatologist. When I tell her about my experience with MMS in my community, she is quick to state that the MMS surgeons in my community and hers practice very differently. Why this is so, I do not know. It has been my experience that when patients learn that their skin cancer can be excised by a plastic surgeon who can do both the excision and reconstruction in one stage and that intravenous sedation is available to them if they wish, most choose this route rather than MMS.

To date, there are no systematic reviews or randomized controlled studies that show MMS to be any better than TE for treating skin cancers.

Until fairly recently, MMS was confined to non-melanoma skin cancers such as basal cell and squamous cell. These are typically confined to a small area of skin and are very rarely life-threatening. While MMS is accepted for routine basal cell and squamous cell skin cancers, its use in melanoma is new and highly controversial.

Recently, dermatologists have begun to perform something called “slow Mohs” for early melanoma cancer. Melanoma is a potentially lethal cancer. Wide excision- taking a generous margin of between 0.5 and 2 cm around the entire cancer, has been the primary treatment for decades. I feel that MMS, which stresses taking thin margins, has no place in treating melanoma. Even with very early, non-invasive melanoma in situ, the accepted standard is wide margins of no less than 5 mm.

The term “slow Mohs” reflects the fact that the process always takes more than one day. Processing a melanoma specimen takes 1-2 days. Therefore, the patient is sent home with their open wound bandaged and made to return a few days or up to a week later for either closure or yet another excision. One patient referred to me had undergone three excisions over the course of three weeks! To me, this is unnecessariy traumatic to a patient and definitely increases the risk of infection. There is no justification for this. When a proper margin is taken at the start, it is uncommon to have to do a second excision.

I spoke to a dermatopathologist who processes a lot of slow Mohs specimens. She dislikes the procedure because of the way the specimen is taken and has to be processed. This makes it difficult, if not impossible, to establish the final margin, which is the closest the melanoma comes to the final surgical margin. Let me stress this: the goal of melanoma cancer excision is not to remove it with the smallest possible margin, which is the goal of slow Mohs; it is to remove the cancer with a generous margin, usually deemed to be 5 mm or more. Most slow Mohs excisions take only a 1-2 mm margin. This small difference can be the difference between curing the cancer and experiencing a recurrence, or worse.

Why the push for slow Mohs in treating a life-threatening cancer? I believe that slow Mohs for melanoma reflects a misguided ordering of priorities. The first priority in treating melanoma is to cure the patient. The concern over reconstruction and the cosmetic result are important, but clearly secondary to that critical primary goal. In 1957 Drs. Harold Gillies and D. Ralph Millard, Jr., two of the pre-eminent plastic surgeons of the last century, wrote, “Too often, the general surgeon will ask courteously whether sparing such and such a bit will make the repair easier. He is genuinely trying to help in the repair and forgetting his primary duty. The answer must be, "I couldn’t care less. You remove the malignancy, so it does not recur, whatever the deformity, and let me worry about the repair”. Because plastic surgeons are trained to deal with even very large facial wounds, we do not concern ourselves over a millimeter or two greater wound, unlike MMS surgeons.

The more cynical side of me thinks that the insurance reimbursement for MMS, which is higher than for traditional excision, is another factor and I believe this same financial incentive leads to MMS being used in situations where it is no better than a TE.

Slow Mohs attempts to force a deadly cancer into the same treatment category as non-melanoma skin cancers, which are not life threatening. Slow Mohs for invasive melanoma is, in my opinion, malpractice. Ask any general or plastic surgeon what they think about slow Mohs and you will hear almost universal condemnation of the procedure. Even among dermatologists, slow Mohs is controversial. The bottom line is that it simply makes no sense and is an example of trying to expand the indication for the procedure beyond anything reasonable or necessary. I would never allow myself or anyone I know to be treated for any melanoma using slow Mohs.

I don’t care for MMS, will never have it done or recommend it to a friend or family member except under very unusual circumstances, believe it is overused, and find it highly inappropriate for treating melanoma.

Richard T. Bosshardt, MD, FACS Senior Fellow at Do No Harm

My book, The Making of a Plastic Surgeon: Two Years in the Crucible Learning the Art and Science, is now available on Amazon as an eBook or paperback. If you have been curious about my world, this is great peek into the most misunderstood surgical specialty.