Mohs Surgey: What To Expect (Learning Series pt. II)

As a Mohs surgeon and member of the American College of Mohs Surgery, I love sharing information about what I feel is a very exciting advancement in skin cancer surgery. In my first post for this Mohs Learning Series, I introduced Mohs surgery by explaining how it differed from traditional skin cancer surgery and its advantages. With Mohs, most of my patients will leave my office fully repaired, with the highest cure rate, a minimal amount of removed tissue, and the least amount of disruption to their daily life.

So how does this happen? In this post, the second in this series, I’m going to walk you through, step-by-step, what my typical Mohs patient can expect before, during, and after the procedure.

Before the surgery is even scheduled, a patient will have permanent section biopsy to determine what kind of lesion is present. This tissue biopsy is sent to a lab in a formalin bottle. Formalin is what we call the liquid that preserves the tissue sample for analysis. There are two ways to prepare tissue for analysis: a formalin bottle or a frozen tissue sample. A formalin bottle sample is more informative at this stage because it allows us to conduct more specialized testing, which provides a broader, clearer picture of the tumor. This helps in planning the appropriate therapy, which may or may not include Mohs surgery, other removal methods, or adjuvant therapy such as lymph node biopsy, chemotherapy, or post-operative radiation. A definitive diagnosis would be more difficult to determine with a frozen tissue sample. Once a diagnosis has been established, if Mohs surgery is appropriate, my patients can expect the following schedule: 

Mohs Surgery: Step-By-Step

Local anesthetic being injected.
Affected area being curettaged.
Incision for mapping.
Affected area is cauterized..
Tissue prepared for freezing.
Prepared biopsy slides.
Surgeon inspecting slides.
Affected area sutured.

1. A patient will meet me ahead of time or sometimes on the day of the surgery at my practice.

2. Once a patient is in the room where the procedure takes place, I talk with them. I administer a local anesthesia to the area where I plan to remove the tumor. 

3. Once the area is ready, I cut a very small piece of tissue. Because of my equipment and training, I’m able to look at 100% of the peripheral and deep margins. This is how a Mohs surgeon refers to the tissue surrounding every side of the tumor. It usually takes around 5 minutes to perform this part of the procedure. It’s a lot like a biopsy.Afterward, we place a small bandage over the wound and ask the patient to wait while we process the tissue.

4. At this point I create a special map of the tissue. This allows me to see exactly where the tumor growth is extending. For example, I’ll say to myself, “I got it all out except at 3:00.” Because I’m the surgeon and I’m the pathologist, I know precisely where the tumor growth is. Then I’ll remove a little bit more tissue in the exact spot where the tumor is extending its growth. If I analyze this and still see microscopic growth, I’ll go a little further. I continue until the tumor is all out. This process is what goes on behind the scenes. Each time I go back to get another piece of tissue, it’s called a stage and the cycle starts all over.

5. Usually the Mohs surgeon will get the entire tumor out on the first removal. Sometimes, however, there are two or three stages for the same surgery. It is very unusual to have more than three stages, but it can happen. Because I’m working with local anesthesia, my patient is completely awake during the process. While I’m analyzing my patient’s tissue, they are in the surgical suite or in the waiting room – either watching television, listening to music, or reading a book.

6. I work with a specially-trained Mohs histotechnician who prepares the slides for analysis. Because the success of a Mohs surgery depends on the quality of the slide, there is absolutely no room for error. The slides must be perfect. The histotechnician uses a special machine to freeze the tissue. When the slide is prepared I read it. By the time all this happens it’s been about 30 minutes. I’ll go back to the patient, numb up the area and remove more tissue at the exact spot where I mapped it. In our example, this would be at the 3:00 position. As I described in my first post, I know exactly where to go to remove more tissue. There is absolutely no risk for miscommunication between the pathologist and surgeon because I am the same person!

7. When the slides indicate a completely clear peripheral and deep margin, I’m done. I’ll numb up the area one last time and repair it. Usually there is only a tiny defect. My patient can then go home. From beginning to end the process takes a couple hours.


I tell my patients that a good analogy for Mohs is that a tumor is like the tip of an iceberg. What you see on the surface may not always be indicative of what’s below. This is why I work with a large team of people. For example, I have a backup dermapathologist. Even if I’m in the middle of a surgery I will not hesitate to ask for a second opinion if I feel I need one. Or if a defect is larger than I anticipated – if I start to get deep into cartilage, bone, or muscle – I’ll contact my network of plastic surgeons or ear, nose, and throat (ENT) plastic reconstructive surgeons. Essentially, if at any point I feel there is someone who can close a defect better than I can, I will call them. They will come and close the defect on my patient that same day or, at the most, the patient will return the next day. Sometimes we choose to let the area heal on its own and not reconstruct it, or reconstruct it at a later date. This is only done when it’s obvious that a superior cosmetic and functional outcome will be achieved by this method and only with the approval of the patient, as good wound care is an important part of the healing process. Not all Mohs surgeons use an extensive network to assist them, so unless you find a Mohs surgeon who does, this level of additional quality control may not be something you can expect. I will educate you on how to select the best-qualified Mohs surgeons in a later post.

Traditional cancer surgery requires a larger cut. Recovery time is longer, and usually a patient has to wait a week to find out the results. If the tumor isn’t out the patient has to return for another surgery. Compare this to Mohs where a patient undergoes the complete procedure on the same day and goes home with a 99% cure rate. I recommend watching a video on the National Skin Cancer Foundation’s web site that illustrates exactly how a Mohs surgery is conducted.

For my part, it feels immensely gratifying to give my patients the benefits of Mohs surgery. Mohs effectiveness and sensitivity to patients’ needs stems from its history. I will cover the fascinating history of Mohs and how it evolved into what it is today in my next Mohs Learning Series post.

Published on 10/11/2011 | Last updated on 10/18/2018