Removing skin cancer while protecting what’s healthy.

In a standard excision, the surgeon removes the visible cancer along with a predetermined margin of surrounding skin, and the specimen is sent to a laboratory. Results come back days later, and a small proportion of cases require a second procedure.

In Mohs surgery, the surgeon is also the pathologist. The tissue is removed, mapped, processed and examined microscopically while you wait, so the margin is confirmed before the wound is repaired. If cancer remains along one edge, only that edge is removed in the next stage.

This matters most on the face, ears, nose, eyelids, lips, hands, feet and other areas where every millimeter of healthy tissue is functionally or cosmetically important — and it is why Mohs surgery is associated with high cure rates for the cancers it is used to treat.

Mohs surgery is a highly specialized procedure for the total removal of skin cancer. There are three surgical steps to each layer, or pass, of Mohs surgery:

1. The surgical removal of the visible portion of the skin cancer with excision or curettage.
2. The surgical removal of a thin layer of tissue at the bed and complete outer margin of the cancer.
3. The examination of the excised tissue by your surgeon under the microscope once it has been processed in our lab.

By examining the entire periphery — the deep and side edges of the tissue, like the outside of a bowl — the surgeon is able to trace out and locate any additional areas of cancer remaining. Before the tissue is examined, it is marked with colored dyes to distinguish top from bottom and right from left, so we can pinpoint the location of any remaining tumor during the microscopic examination. If more cancer is present, the procedure is repeated — and only the area of remaining cancer is removed.

Using microscopic examination, the surgeon pinpoints the areas involved with cancer and selectively removes only those areas. In this way, skin cancer is traced out to its roots — preserving as much normal tissue as possible with the highest chance for cure.

Because Mohs surgery uses complete, systematic microscopic control to search out the roots of the cancer, it cures almost all patients — 97–99%, depending on the type of cancer — even those in whom skin cancer has persisted in spite of several other treatments.

General excisions sent to a pathology lab are cut differently, and only a small portion of the margins is checked for cancer in comparison. The margins we take are larger in order to get a rate of approximately 95% clear margins.

Learn more about Mohs surgery from the ASDS↗

• Skin cancer on the face, ears, nose, eyelids, lips, scalp, hands, feet or genitals
• Cancer that has recurred after previous treatment
• Tumors with aggressive or infiltrative features under the microscope
• Cancers with poorly defined borders
• Large tumors, or those in areas where preserving tissue is critical
• Patients who are immunosuppressed or have had multiple skin cancers

Not every skin cancer needs Mohs surgery. Many are treated well with a standard excision or another approach, and Dr. Gaul will recommend the option that fits your tumor rather than defaulting to the most involved one.

1. Arrival and planning. The site is confirmed with you, photographed for the record, and the plan is reviewed.
2. Local anesthetic. The area is numbed. You remain awake and comfortable throughout.
3. First stage. The visible cancer is removed with a thin margin. A temporary dressing is placed and you wait in the office.
4. Mapping and microscopy. The tissue is precisely oriented, processed into slides and examined by Dr. Gaul. This typically takes about an hour.
5. Additional stages if needed. If cancer remains at a specific edge, only that area is re-numbed and removed, then re-examined. Most cases require one to three stages.
6. Reconstruction. Once margins are clear, the wound is repaired — by direct closure, a skin flap, a graft, or by allowing it to heal on its own where that gives the best result.
7. Instructions and follow-up. You leave with a dressing, wound care instructions and a follow-up plan.

Mohs surgery is generally safe and well tolerated, and like any surgical procedure it has risks: bleeding, bruising, infection, pain, scarring, wound healing problems, temporary or rarely permanent numbness or changes in sensation, and — depending on the location — effects on nearby structures such as nerves or eyelid position.

Recurrence is uncommon but possible, which is why follow-up examination remains part of your care. Dr. Gaul will review the risks specific to your tumor and its location with you before surgery, and you will have the opportunity to ask questions.

• Set aside the full day; the length depends on how many stages are needed
• Eat breakfast, bring lunch or a snack, and bring something to read
• Wear comfortable clothing that buttons rather than pulls over the head
• Arrange a driver if the surgery involves the area around the eyes, or if you prefer
• Plan to avoid strenuous activity for a period after surgery

Detailed pre-operative and post-operative instructions specific to your surgery are provided by our office. Please follow those instructions, and call us at any point if something is unclear.

This page is general education and is not medical advice, diagnosis or treatment, and it does not create a physician–patient relationship. Individual circumstances differ; please discuss your own skin with a qualified clinician. If you are having a medical emergency, call 911.