Mohs surgery

Mohs surgery is also known as Mohs micrographic surgery. It is a surgical procedure that removes a tumour little by little in layers until no cancer remains. The goal is to remove the cancer and leave as much healthy tissue as possible.

Why Mohs surgery is done

Mohs surgery may be used to treat different kinds of skin cancers, including basal cell carcinoma, squamous cell carcinoma, some types of melanoma and other rare types of skin cancer. It is used to treat tumours:

  • in areas where it is important to remove as little tissue as possible (such as the eyelids, ears, nose, lips, hairline, genitals, fingers or toes)
  • that are larger (to leave a smaller scar)
  • that have come back (recurred) or have a high risk of coming back
  • in sites of previous radiation therapy or where there is a scar
  • that are growing quickly
  • in people with immunosuppression
  • with poorly defined edges (margins)

How Mohs surgery is done

Mohs surgery is usually done as an outpatient procedure in a doctor’s office or hospital.

Local anesthetic is used to freeze the area. The surgeon uses a scalpel to remove the part of the tumour that can be seen along with a thin layer of tissue underneath. A temporary bandage is placed on the cut (incision).

The tissue sample is taken to the lab to be looked at under a microscope to find out if there are still cancer cells in the tissue.

If there is cancer in the layer, another thin layer of tissue is removed and examined. Each round takes about an hour. The surgery takes 20 to 30 minutes and looking at the tissue under the microscope takes about 30 minutes.

These steps are repeated until the last tissue sample removed shows no cancer cells and there is a surrounding margin of healthy tissue.

The wound is repaired after all of the cancer is removed. Repairing the wound might include:

  • leaving the wound to heal on its own
  • closing the wound with stitches
  • using a skin graft or skin flap to cover the wound
  • seeing a plastic surgeon to repair the area (if surgery was extensive)

Side effects

You may have side effects after surgery, but everyone’s experience is different. Side effects can happen any time during, immediately after or a few days or weeks after Mohs surgery. Side effects may include:

  • pain, tenderness or a burning sensation
  • swelling
  • bleeding and bruising
  • infection
  • scarring
  • nerve damage such as numbness

Tell your healthcare team if you have these side effects or others you think might be from surgery. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.

Expert review and references

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

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