Mohs Micrographic Surgery: What is it?

Mohs Micrographic Surgery Treats Skin Cancer

Mohs micrographic surgery, pronounced moes, is a technique for removing skin cancer that is more complicated than simply picking up a scalpel and cutting the offending growth off. The technique was developed in the 1930’s by Dr. Frederick Mohs and hasn’t changed much since. It’s indicated for squamous cell carcinomas, basal cell carcinomas, and some other less common skin cancers. Mohs surgery is not widely used to treat melanoma. (1)

Mohs surgery is indicated for skin cancers in cosmetically sensitive regions (like the face) or for regions where removing large pieces of skin would result in a bad outcome. The great thing about Mohs surgery is that you can know you’re cured right then and there. Cure rates are over 98% for squamous and basal cell carcinomas.

What can I expect the day of?

Read this handy infographic for the short version.


As with any medical procedure, there will be paperwork to fill out. After getting the formalities over with your doctor will start by providing anesthesia to the area with lidocaine. The pinprick from the needle will not be painful; however, there will be a burning sensation as the lidocaine is injected into the area. The lidocaine works instantly so the pinches from the needle will be duller. If you’ve ever had a dental procedure done with lidocaine, the feeling will be very similar.

Mohs Micrographic Surgery Spares Health Tissue

Next, the dermatologic surgeon will get ready for the first round of excising your skin cancer with a scalpel. He or she will try to cut as close to the borders of cancer as possible so all possible healthy skin is spared. Your doctor will stop any bleeding and cover the wound with gauze and tape. Some preliminary stitches may be necessary to stop any excessive bleeding.

The sample of skin cancer that is removed will be marked in the orientation in which it was removed. This means your doctor knows where the top, bottom, left, and right sides of cancer originally were. This will allow your dermatologic surgeon to remove more tissue only from the areas that still have cancer.

The sample from Mohs micrographic surgery is analyzed the same day.

The sample is immediately taken to a back room where a technician trained in preparing these skin cancer samples will freeze and stain it. There is a special machine that cuts the tissue into very thin slices. Another machine is able to flash-freeze the tissue. Once the tissue is put onto a slide, stained, cut, and frozen, the dermatologic surgeon can view it under a microscope. Since the slide is stained a different color in each ordinal direction (north may be yellow, south may be blue, etc) your doctor will keep this orientation in mind as he/she views the slide. The doctor will be looking at the borders to make sure there are no cancer cells present.

While this process is occurring in the background, you will be in the waiting room or a patient room. You can read a book or play on your phone until you’re called back to either close your wound or remove another piece of tissue.

What if there is still cancer present?

Let’s assume there were still cancer cells present in the top right area. Your doctor will bring you back into the procedure room and cut another small piece of skin from the top right area. The process of preparing the sample and reviewing it under the microscope will occur again. This will go on until all of the borders are clear. There is usually between 1-3 cycles of tissue removal and analysis.

Closing the Surgical Defect

Once the cancer has been completely removed (woo-hoo you’re cured!) it’s time to close the site of excision. Your doctor won’t know exactly how much he/she has to remove or how deep it will be until the day of the procedure. Depending on the location of the wound, the depth, and the size, the dermatologic surgeon has a variety of closure options. You will need stitches and more lidocaine in order to close.

It’s amazing the kind of reconstruction that a dermatologic surgeon can do. I once saw a skin cancer on the nose of the patient that involved part of the cartilage that keeps your nostrils open. Due to the extensive invasion of cancer, much of the nostril had to be removed and the cartilage within. In order to maintain the stiffness needed to keep the nostril open with cartilage, the dermatologic surgeon used cartilage from the ear and transplanted it to the nose. This is all on an outpatient basis with local anesthesia.

Why doesn’t my dermatologist use Mohs surgery every time?

For one thing, it’s much more expensive than simple excision with borders or electrodesiccation and curettage. Your doctor has to spend a lot more time preparing and analyzing the skin samples behind the scenes. As a result, your insurance won’t cover Mohs surgery for every skin cancer.

Some of the current controversies lie in the overuse of Mohs surgery in skin cancers that could be easily removed by simple excision but are removed by Mohs instead. Dermatologists have an incentive to provide Mohs surgery because they can bill significantly more for the procedure.

Guidelines for When to Use Mohs

The American Academy of Dermatology, in association with the several dermatologic surgery organizations, has developed a set of guidelines for which skin cancers and in which locations require Mohs surgery. (2) They have even developed an app that your doctor can use to decide whether Mohs surgery is the best option. In the example below, a recurrence of aggressive basal cell carcinoma on the nose (H area) has the highest score of possible for appropriateness of Mohs surgery.

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Are dermatologic surgeons as good as plastic surgeons?

Dermatologists who want to become Mohs surgeons must complete additional training after their residency in order to become proficient in the surgical techniques necessary in Mohs surgery. You should rest assured that your dermatologic surgeon has the appropriate training and expertise to make you look the best possible after your surgery. It always helps to go to a trusted doctor. Ask your friends or your current dermatologist for a good recommendation.

In fact, a study that I read a few years ago had both plastic surgeons and dermatologic surgeons rate the cosmetic results from after skin cancer removal and there was no difference between the two in results. Unfortunately, I could not find the paper again for reference.


  1. Skin Cancer Foundation. The Evolution of Mohs Micrographic Surgery.
  2. American Academy of Dermatology. Mohs Surgery AUC.

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