A walk through the day of Mohs surgery: who qualifies, how the layers and lab checks work, cure rates, wound repair, and its use for melanoma in situ on the face.
Mohs surgery removes a skin cancer one thin layer at a time and checks each layer under a microscope before anyone decides whether to take more. The surgeon stops as soon as the edges are clean. You arrive with a cancer and, in most cases, leave the same day with it fully removed.
One doctor acts as surgeon, pathologist, and often the person who repairs the wound.
Mohs surgery takes more time and staff than a standard excision, so doctors reserve it for cancers where it pays off. In 2012 the American Academy of Dermatology and 3 surgical societies published appropriate use criteria that rated 270 clinical scenarios. In plain words, Mohs is considered appropriate for basal cell and squamous cell carcinomas that are:
A small, low-risk cancer on the trunk, arm, or leg of a healthy person usually falls outside the criteria. Simpler treatments cure those tumors at a high rate.
Eat breakfast and take your usual medicines unless your surgeon told you otherwise. Bring a book and a snack, because most of the day is waiting.
The surgeon marks the visible tumor and numbs the area with local anesthetic. You stay awake. Using a scalpel, the surgeon removes the visible cancer with a very narrow rim of skin, cutting at an angle so the specimen looks like a shallow saucer. A nurse places a temporary bandage and you return to the waiting room.
The tissue goes to a lab inside the office. A technician marks its edges with colored inks, draws a map that matches the wound, freezes the tissue, and slices it so that the entire outer edge and the entire underside land on glass slides. Preparing the slides takes about an hour.
This cutting pattern is the heart of the method. In a standard excision the pathologist samples the margins at intervals, like checking slices of a loaf. In Mohs the surgeon sees 100% of the margin.
When cancer shows at any point on the slides, the map tells the surgeon exactly where in the wound that point lies. You go back to the room, get more anesthetic if needed, and the surgeon removes another thin layer from that spot only. Then you wait again. Many cancers clear in 1 or 2 rounds. A tumor with long roots can take more, and the visit can stretch to several hours or the whole day.
The Skin Cancer Foundation reports cure rates of up to 99% for skin cancers that have never been treated before and up to 94% for cancers that came back after earlier treatment. These are the highest rates of any treatment for basal cell and squamous cell carcinoma.
Repair is planned only after the cancer is out, since the final size of the wound is unknown until then. The options run from simple to complex:
Most Mohs surgeons repair the wound the same day. For larger wounds, or wounds on the eyelid or deep in the nose, the surgeon may arrange for an oculoplastic, facial plastic, or plastic surgeon to do the repair, sometimes a day or 2 later.
For years Mohs was seldom used for melanoma. Melanocytes, the pigment cells that melanoma comes from, are hard to tell apart from their neighbors on frozen slides with routine stains. Immunostains changed that. A stain called MART-1 colors melanocytes so they stand out, and the lab can run it on frozen tissue the same day.
Use of Mohs with immunostains has grown for melanoma in situ on the head and neck, especially the lentigo maligna type, which often spreads well past its visible border. In the 2012 appropriate use criteria, 10 of the 12 scenarios for lentigo maligna and melanoma in situ were rated appropriate for Mohs. Reviews that pool published studies report local recurrence after Mohs that is at least as low as after wide excision. Those studies were not randomized, so more data is needed.
NCCN guidelines still advise against Mohs for invasive melanoma when standard margins can be taken, and they allow it to be considered for the thinnest invasive melanomas in tight anatomic areas. Some centers use a related method called slow Mohs or staged excision, in which the edges go to a pathology lab overnight and the wound is repaired once the margins are clear.
You leave with a bulky pressure bandage that stays on for 24 to 48 hours. Swelling and bruising peak around day 3 or 4, and surgery near the forehead or nose can swell the eyelids. Acetaminophen controls the pain for most people.
Plan on a quiet week with no heavy lifting, bending, or hard exercise. Stitches come out in 5 to 10 days. The scar keeps improving for 12 to 18 months.
