Reviewed by: HU Medical Review Board | Last reviewed: February, 2022. | Last updated: August 2022
Mohs surgery is a procedure used to remove skin cancer layer by layer. Mohs surgery treats tumors that are large, invasive, or likely to recur.1,2 It has the highest cure rates in non-melanoma skin cancer and saves the most healthy skin.1,2 Because it requires multiple steps, it can be expensive. This procedure is also called Mohs micrographic surgery or abbreviated MMS.
How is Mohs surgery performed?
A Mohs surgeon is a dermatologist who has had 1 to 2 years of additional training in this type of surgery. Mohs surgeons have expertise that combines cancer surgery, pathology, and reconstructive surgery.3
Mohs surgery is done by removing one layer of skin at a time (Figure).4 Your surgeon examines each layer under a microscope. She or he looks at the edges and the underside of the tissue. The purpose of examining it is to see whether there are any cancer cells. If there are cancer cells, your surgeon removes another layer of tissue. Your surgeon will remove tissue only from the section where cancer cells were found. This process of removing one layer after another continues until the sample contains no cancer cells.2 Another term for this is “clear margins.” Most tumors are removed in 1 to 3 stages.3
Figure. Mohs Surgery
Once the cancer is gone, you and your surgeon will discuss the repair.3 Options include:
- Letting small incisions heal on their own
- Closing larger incisions with stitches
- Closing complicated wounds with a skin graft or flap
- Referring you to a reconstructive (plastic) surgeon
For what types of skin cancer is Mohs surgery used?
Mohs surgery is often used to treat:
- High-risk basal cell carcinoma (BCC) or squamous cell carcinoma (SCC)
- BCC or SCC that need re-treatment
- Some melanomas with unclear borders
- Some Merkel cell carcinoma
- Cancers on locations where function and scar appearance are important
High-risk BCC or SCC are likely to return (recur), so Mohs surgery is the first choice of treatment.5,6 The margins are evaluated during the surgery to ensure that all cancer cells are removed. Mohs surgery cures 99% of BCC and 97% of SCC.5
Mohs surgery is also used for re-treatment of BCC or SCC. Low-risk BCC or SCC tumors are sometimes removed with standard excision. After the surgery, the pathologist will check the tissue sample. If cancer cells are at the tissue edges, a second surgery is necessary. Mohs surgery is one option for re-treatment.5,6
Some melanomas are treated with Mohs surgery. This surgery is useful when the border of the tumor is hard to see. Examples include melanoma that is in the top layer of skin only (melanoma in situ) or lentigo maligna melanoma.7
Mohs surgery is used when it is important to save as much healthy tissue as possible.2,3,8,9 Examples include removing skin cancers on the central face, hands, or feet.2,8,9
What should I expect before, during, and after the procedure?
Mohs surgery is an outpatient procedure. Your doctor will numb the affected area (local anesthesia).3 The surgery may take several hours. The process of preparing and examining each layer is time consuming. Bring a book to help pass the time while you are waiting!
Post-operative care depends on the type of repair you have. Your surgeon will instruct you on caring for the wound at home.
What are the risks of Mohs surgery?
The possible risks of Mohs surgery include:10
- Nerve damage
- Graft failure
What questions should I ask before Mohs surgery?
Here is a list of questions you should ask before your Mohs surgery:
- Are you trained as a Mohs surgeon? How many of these procedures have you done?
- What makes me a good candidate for Mohs surgery?
- What type of repair do you think I will need?
- What type of anesthesia will you use during the procedure?
- What do you expect the scar will look like?
- How can I minimize scarring?
- How long will the incision take to heal?
- What should I expect for my recovery?
- How much will my procedure cost?
- How often should I have follow-up exams with my dermatologist to check for cancer recurrence or a second skin cancer?