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Mohs Surgery

Mohs surgery is also known as Mohs micrographic surgery. It is a specialized surgical procedure that involves removing the tumour little by little in layers until no cancer remains.

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.

Mohs surgery is used to treat tumours:

  • in areas where it is essential to remove as little tissue as possible (such as the eyelid, ears, nose, lips, hairline, genitals, fingers or toes)
  • that are larger (greater than 2 cm in diameter)
  • that are recurrent or have a high risk of recurrence
  • occurring in sites of previous radiation therapy
  • that are aggressive
  • in immunosuppressed people
  • with poorly defined borders

How Mohs surgery is done

Mohs surgery is usually done on an outpatient basis, either in a medical office or hospital.

  • Local anesthetic is used to freeze the area.
  • The surgeon uses a scalpel to remove the visible part of the tumour along with a thin, underlying layer of tissue that is slightly larger than the visible tumour.
  • Before the tissue is completely removed, the surgeon makes shallow cuts (hash marks) with a scalpel to help identify the area from where the tissue was removed.
  • A temporary bandage is placed on the incision.
  • The surgeon takes the tissue to the laboratory where:
    • The surgeon cuts the tissue sample into sections and marks them to show their location.
    • The location of each section is mapped on a Mohs map and used as a reference point for the surgeon.
    • The sections are frozen, cut into very thin slices, placed onto slides and stained.
    • The slides are examined under a microscope to check for the presence of cancer cells.
      • If cancer cells are found, the surgeon notes the location on the Mohs map.
      • The surgeon uses the map as a guide to remove an additional layer of tissue from the skin, while leaving as much healthy tissue as possible.
  • If cancer cells remain, another thin layer is removed, mapped and examined.
  • These steps are repeated until the last tissue sample removed shows no cancer cells.
  • The wound is repaired after all of the cancer is removed. This 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
  • If surgery is extensive, the person may be referred to a plastic surgeon for reconstruction.

Potential side effects

Complications from Mohs surgery are uncommon. Side effects can happen any time during, immediately after, or a few days or weeks after Mohs surgery. Most side effects go away after Mohs surgery. Late side effects can occur months or years after surgery. Some side effects may last a long time or be permanent.

It is important to report side effects to the healthcare team.


Pain often occurs because of trauma to the tissue during surgery. Nerve pain may occur after surgery done on tissues close to the nerves. Nerve pain can appear long after surgery is over and may last a long time. Pain-relieving medications are used to control pain. It may take time for pain to decrease after surgery, depending on the procedure done and how the person heals or tolerates pain. Check with the doctor if pain does not go away or pain medications do not relieve the pain.


Some swelling may occur, depending on the area treated. The area may be very delicate when it heals. If a skin graft or skin flap is done, it is very important that the area is not damaged while it is healing.


A small amount of bloody drainage may be expected after surgery. Report large amounts of blood to the doctor or healthcare team.


Some people may develop a wound infection after surgery. This is not a common side effect, but it can potentially occur after any type of surgery. Antibiotics may be used to help prevent or treat an infection.

Tell your doctor or the healthcare team about signs of infection, such as redness, pus or foul-smelling drainage, increased swelling or tenderness at the treatment site and increased temperature (fever).


There may be scarring of the skin in the treated area. Scars may be visible for a long time or may be permanent, but they can often fade over time.


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