Mohs micrographic surgery is the most effective treatment for basal cell and squamous cell carcinomas. The procedure involves the layer-by-layer removal of skin cancer, and it has a 99% cure rate for previously untreated skin cancers.

Mohs micrographic surgery, or Mohs surgery, is a complex procedure where a surgeon takes a microscopic analysis of tissue cells.

During Mohs surgery, the surgeon removes individual layers of tissue until no cancer remains. This technique allows them to remove a tumor or lesion without harming the surrounding, healthy tissue.

This article explains the goal of Mohs surgery, its potential benefits and risks, and what a person can expect during and after the procedure.

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Frederic Mohs, M.D., developed Mohs surgery in the 1930s. It is a technical surgical procedure that dermatologists use to treat skin cancer.

During the procedure, a dermatologist or specialist Mohs surgeon removes and examines each layer of cancerous tissue under a microscope until only cancer-free tissue remains.

Mohs surgery aims to eliminate as much skin cancer as possible while keeping the surrounding tissue intact.

The surgery is also unique because it allows the surgeon to see where the cancer stops, which is not possible with other skin cancer treatment techniques.

According to the Skin Cancer Foundation, Mohs surgery is the most effective technique for treating basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs), two of the most common types of skin cancer.

In addition to basal cell carcinoma, melanoma, and squamous cell carcinoma, Mohs surgery can treat rarer forms of skin cancer, including dermatofibrosarcoma protuberans, extramammary Paget’s disease, and Merkel cell carcinoma.

Surgeons recommend Moh’s surgery for skin cancers that:

  • are located in areas with thin tissue, such as around the eyes, ears, nose, mouth, hands, feet, or genitals
  • are large, aggressive, or both
  • return following a previous treatment
  • develop in an area where scar tissue is already present
  • have borders that are hard to define
  • involve a patient who is immunocompromised
  • have occurred in patients who have had previously irradiated skin

Unlike routine excisional surgery, Mohs surgery is an outpatient procedure that surgeons perform in stages while the patient waits between each stage.

Before surgery, the surgeon may outline the patient’s lesions with a body-safe ink to map the tumor. Once they have injected the patient with a local anesthetic, they will remove the smallest layer of cancerous tissue.

As the patient waits, a team will process the layer of removed cancerous tissue in an onsite pathology laboratory.

After processing, the surgeon examines the tissue to determine whether or not any cancer remains. If cancer remains, the surgeon will repeat the process until they have removed all the cancerous tissue.

All surgeries come with some degree of risk.

Potential risks of Mohs surgery include:

  • pain or tenderness around or at the surgical site
  • discoloration
  • bleeding
  • scarring at the surgical site
  • infection
  • allergic reaction

Although Mohs surgery is the standard for removing BCCs and SCCs, complications can still occur, which include:

  • cosmetic or functional abnormalities, if the surgical site is near a sensitive structure such as the eyes or eyelids, nose, ears, or lips
  • nerve damage
  • an enlarged scar or keloid

According to the American Academy of Dermatology, most Mohs surgeons are dermatologists who have completed extensive training, also known as a fellowship, in Mohs surgery.

The Skin Cancer Foundation notes that a surgeon may ask an individual to prepare for Mohs surgery by:

  • wearing comfortable clothing
  • refraining from taking aspirin and other nonsteroidal anti-inflammatory drugs or other blood thinners 10 days before surgery
  • avoiding alcohol a few days prior to surgery
  • avoiding taking vitamin E a few days before surgery
  • getting a good night’s sleep
  • eating a normal breakfast
  • bringing a book, magazine, or something else to help pass the time
  • clearing their schedule on the day of the procedure
  • asking a friend or family member to accompany them to their appointment

A person who is due to undergo the procedure should also discuss their allergies, existing health conditions, and current medications with their doctor before receiving Mohs surgery. This is especially true for people who have preexisting cardiovascular disease.

Mohs surgery is an outpatient procedure that surgeons perform under local anesthesia.

After the anesthetic takes effect, the surgeon will use a scalpel to remove a thin layer of cancerous tissue. Removing the first specimen only takes a few minutes.

The surgical team will then bandage the open wound temporarily and ask the patient to wait while the lab work begins. This waiting period could last for up to an hour or longer. If more than two rounds are necessary, the entire process could last several hours.

If the cancer remains, the surgeon will repeat the process until the area is free of cancer. According to the Skin Cancer Foundation, surgeons generally complete 40–50% of Mohs procedures within the first stage.

Once the patient is cancer-free, the surgeon will determine the best way to repair the area. If the surgical site is small, they may suggest leaving it to heal naturally or close it using stitches.

In some cases, the wound may need reconstruction with a skin flap or skin graft from another part of the person’s body.

If the surgical site is extensive or complex, the surgeon may refer individuals to another surgeon for reconstructive surgery.

They will also provide detailed post-operative instructions, such as taking 24–48 hours to rest.

The chief advantage of Mohs surgery is that someone who undergoes the surgery will experience immediate results.

Another advantage is that the procedure is a tissue-sparing procedure, making it suitable for areas where the skin is thin or delicate.

According to the American College of Mohs Surgery, the cure rate exceeds 99% for new skin cancers and 95% for recurrent skin cancers.

Mohs surgery is an advanced outpatient procedure that allows surgeons to remove cancerous tissue layer by layer. The technique allows surgeons to save as much of the patient’s healthy tissue as possible, and afterward, the patient can leave the office after the removal of the cancerous tissue.

However, there is always a small risk of cancer recurrence — less than 1% — or developing another skin cancer.

While not every person with skin cancer can have Mohs surgery, the procedure is the gold standard for treating BCCs and SCCs, particularly on the face and other delicate body parts.

The Skin Cancer Foundation recommends Mohs surgery to treat BCCs or SCCs that appear around the eyes, nose, lips, ears, scalp, fingers, toes, or genitals.