Understanding Mohs Surgery

Mohs surgery is used to treat certain kinds of skin cancer. It's named for Dr. Frederic Mohs, who developed it in the 1930s. This surgery is done in stages. The goal is to leave as much healthy skin as possible.

During the surgery, a very thin layer of the tumor and a small area around it are removed. The removed tissue is looked at right away under a microscope. If cancer cells are seen, another layer from that exact area is removed and checked in the lab. This process is repeated until no more cancer cells are found.

During standard, non-Mohs surgery, the tumor and what looks to be an edge of normal, healthy tissue around it (called a margin) are removed and sent for testing. The goal is that no cancer cells will be found in the margin. If they are, more surgery or other kinds of cancer treatment will be needed.

In contrast, Mohs surgery slowly and precisely removes the tumor in layers that are examined right away. This makes it more likely that all the cancer is removed. It also lowers the chance of it coming back. Mohs surgery lets the healthcare provider protect more healthy tissue than with standard tumor removal. This means there's less scarring, too.

Why Mohs surgery is done

Mohs surgery is most often used for basal cell cancers and squamous cell cancers on the skin that are:

  • Large or fast-growing

  • Likely to spread

  • Likely to come back, or have come back after treatment

  • On an area where it's important to remove as little tissue as possible (like the nose, lips, ears, eyelids, scalp, genitals, feet, or hands)

  • Surrounded by edges or borders that are hard to see

Some healthcare providers use Mohs surgery to treat certain small melanoma skin cancers.

How Mohs surgery is done

The surgery is most often done in an office or surgery center. It's an outpatient procedure. This means you go home after the surgery is done. Still, the surgery can take several hours. During the surgery:

  • You might change into a patient gown or stay in your regular clothes. Your body will be positioned so that the healthcare provider can get to the area that needs treatment.

  • The area to be treated might be marked with a pen.

  • A drape or cover is put over the area and a bright light is used to see it.

  • You'll stay awake during this surgery. A tiny needle is used to put numbing medicine into the area around the tumor. This keeps you from feeling pain during the surgery.

  • A small, sharp knife, called a scalpel, is used to remove the first layer of tissue. The area is covered with a small bandage while you wait.

  • You might stay in the procedure room or move to a waiting area.

  • The tissue is examined in a lab to see if and where cancer cells might be left. This can take an hour or longer. During this waiting time, you can read or watch TV.

  • If cancer cells were seen, you go back to the surgical room and more numbing medicine is injected, if needed. Then another layer of the tumor is removed and checked in the lab.

This process is repeated until no cancer cells are found in the removed tissue. Once the tumor is totally removed, you and your surgeon can decide how best to repair the surgery site. The repair may be done right away, or it may be planned for another day.

Risks of Mohs surgery

  • Bleeding

  • Infection at the surgery site

  • Nerve damage

  • Pain

  • Problems with reconstruction

  • Rarely, the skin cancer comes back, and more treatment is needed

  • Reopening of the incision after surgery

  • Scarring

  • Severe bruising

Online Medical Reviewer: Jessica Gotwals BSN MPH
Online Medical Reviewer: Kimberly Stump-Sutliff RN MSN AOCNS
Online Medical Reviewer: Michael Lehrer MD
Date Last Reviewed: 3/1/2022
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