The Story Behind the Technique
Mohs surgery was developed in the 1930s by Dr. Frederic Mohs, a surgeon at the University of Wisconsin. He noticed that many skin cancers recurred after standard surgery because invisible cancer cells were left behind at the edges of the wound. Dr. Mohs created a method that allowed surgeons to look at every edge of tissue before closing the wound. A revolutionary idea that changed skin cancer treatment. Over the following decades, the technique was refined and simplified, and today it is practiced by fellowship-trained Mohs surgeons at clinics around the world.
Why Standard Surgery Misses Cancer Cells
When skin cancer is removed with a standard excision (cutting it out with a safety margin of normal-looking skin), only a small sample of the edges is sent to a pathology lab and checked under a microscope. Because of the way tissue is processed, roughly 1% of the actual wound edge is examined. The rest is inferred. This means that narrow channels of cancer cells, which are not visible to the naked eye, can sometimes be missed. Mohs surgery solves this problem by examining 100% of the wound edge in the same visit, leaving no guesswork.
Helpful Tips
- Standard excision checks roughly 1 out of every 100 sections of the wound edge.
- Mohs surgery maps and examines every section of the wound edge before closing.
The Mohs Cycle: Step by Step
Mohs surgery is performed in a series of carefully controlled steps called stages. After your surgeon numbs the area with a local anesthetic (a numbing injection similar to what a dentist uses), the process begins. You stay in the clinic throughout and are kept comfortable between stages.
Step 1: Remove
Your surgeon carefully removes a thin layer of tissue that includes the visible tumor plus a very thin margin of surrounding skin. The layer is taken as flat and thin as possible to preserve healthy tissue. A temporary bandage is placed over the wound while the tissue is processed.
Step 2: Map
The removed tissue is precisely marked with colored dyes and a detailed diagram. Called a Mohs map. Is drawn. This map acts like a compass, recording exactly where each piece of tissue came from on your skin so that any positive area can be pinpointed precisely.
Step 3: Examine
The tissue is frozen and cut into very thin sections in an on-site lab. Your surgeon then looks at these sections under a microscope, checking every millimeter of the cut edge. This is why Mohs surgeons are trained in both surgery and pathology (the study of tissue under a microscope). The entire process typically takes 45–90 minutes per stage.
Step 4: Repeat or Close
If cancer cells are found at any edge, the map tells the surgeon exactly where they are. Only that small area is removed in the next stage. Healthy skin everywhere else is left alone. This cycle repeats until the edges are completely clear. When no cancer cells remain, the wound is closed, usually on the same day.
Cure Rates and Why They Are So High
Because Mohs surgery removes cancer with complete margin control, it achieves cure rates that are higher than any other single-stage treatment for skin cancer. For basal cell carcinoma (BCC), the most common type of skin cancer, the 5-year cure rate for a first-time (primary) tumor is approximately 99%. For squamous cell carcinoma (SCC), the second most common type, the cure rate for a primary tumor is approximately 97%. For tumors that have come back after previous treatment (recurrent tumors), Mohs also outperforms other options, with cure rates of about 94% for BCC and 90% for SCC.
| Tumor Type | Primary Tumor | Recurrent Tumor |
|---|---|---|
| Basal Cell Carcinoma (BCC) | ~99% | ~94% |
| Squamous Cell Carcinoma (SCC) | ~97% | ~90% |
Local Anesthesia: What to Expect
Mohs surgery is performed entirely under local anesthesia. A numbing medicine injected directly into the skin around the tumor. You will be awake during the procedure and able to talk with the surgical team. The injection itself causes a brief stinging sensation that fades within seconds as the area becomes numb. You will feel pressure and movement but no pain while your surgeon works. Most patients are surprised by how comfortable the experience is. Because the procedure can take several hours with waiting time between stages, you are encouraged to bring a book, tablet, or headphones.
Helpful Tips
- The numbing injection takes effect in under a minute.
- You may eat a normal meal before surgery unless told otherwise.
- Bring something to occupy yourself during waiting periods between stages.
Tissue Conservation: The Key Advantage
Because Mohs surgery checks all edges in real time, your surgeon only removes tissue that actually contains cancer. Standard surgery must use larger safety margins to compensate for the uncertainty of not checking all edges. On cosmetically sensitive areas like the nose, eyelids, lips, and ears, this difference can be very significant. The wound may be considerably smaller with Mohs surgery than it would be with a standard excision. A smaller wound usually means a smaller scar and better function of the affected area. This tissue-sparing quality is one of the main reasons Mohs surgery is preferred for tumors on the face, hands, feet, and genitalia.