John D. Boyer, M.D.

Mohs Frequently Asked Questions

Mohs surgery is the most effective treatment for most types of skin cancer. We have provided answers to several common questions about Mohs skin cancer surgery below.

The term “Mohs” refers to Dr. Frederic Mohs, Professor of Surgery at the University of Wisconsin, who developed this surgical technique in the 1930s. The technique has undergone many refinements and has come to be known as “Mohs micrographic surgery” or simply “Mohs surgery” in honor of Dr. Mohs.

Dr. Mohs recognized that a skin cancer often resembles the “tip of the iceberg” with more tumor cells growing downward and outward into the skin like the roots of a tree. These “roots” are not visible with the naked eye, but can be seen under a microscope.

Mohs Surgery is a highly specialized and precise treatment for skin cancer in which the cancer is removed in stages, one tissue layer at a time. It is an outpatient procedure, performed under local anesthesia, and is distinguished by a specific technique of tissue examination that is unique to Mohs surgery. Although other surgical specialists may check excision margins, this form of pathologic examination of the tissue is not the same as Mohs surgery.

Once a tissue layer is removed, its edges are marked with colored dyes, and a map of the specimen is created. The tissue is then processed onto microscope slides by a Mohs histotechnician. These slides are carefully examined under the microscope by the Mohs surgeon so that any microscopic roots of the cancer can be precisely identified and mapped. If cancer cells are seen, an additional tissue layer is removed only in areas where the cancer is still present, leaving normal skin intact. This saves as much normal, healthy skin as possible.

Once the cancer has been removed, the Mohs surgeon will explain options for repair of the wound, including natural healing, stitching the wound together using a side-to-side closure, or using a skin flap or graft.

Yes. Following a biopsy, your skin cancer may no longer be visible. However, the surface lesion that was removed may represent the “tip of the iceberg.” More tumor cells may remain in the skin. These can continue to grow downward and outward, like roots of a tree. These “roots” are not visible with the naked eye. If they are not removed, the tumor will likely reappear and require more extensive surgery (see examples of cited studies below).

Tumors that are neglected can spread deeply into the skin and invade nearby structures. On rare occasions, these cancerous cells can metastasize to lymph nodes and other organs in the body.

Mohs surgery offers the highest cure rate among treatments for skin cancer and can be used for practically any skin cancer type. There are many other acceptable skin cancer treatment options including freezing (cryosurgery), scraping & burning (curettage and electrodessication), surgical removal (excision), and laser surgery. All these procedures require the provider to estimate how big the cancer is and then perform removal or destruction of an additional standard wider margin of healthy appearing skin around the tumor. The numerous advantages of Mohs surgery compared to other skin cancer treatments include its high cure rate and cost-effectiveness. It is especially appropriate for skin cancers that:

  • Develop on areas where preserving cosmetic appearance and function are important
  • Have recurred after previous treatment or are likely to recur
  • Are located in scar tissue
  • Are large
  • Have edges that are ill-defined
  • Grow rapidly

Although Mohs surgery can take longer than other techniques to perform, advances in technology, such as our automated staining of tissue samples, have made it quicker. While it is impossible to predict exactly how much time to expect for each Mohs surgery procedure, the entire procedure usually lasts several hours. Rarely, clearing the tumor and reconstructing the defect can take the better part of a day. A consultation with our Mohs surgeons prior to your procedure will allow for the surgeon to understand the unique qualities of your situation and enable him to more clearly estimate the extent of the timeframe for the surgery.

Yes. As will any treatment for skin cancer, Mohs surgery will leave a scar.

Mohs surgery preserves as much healthy skin as possible and maximizes options for repairing the surgical defect, once the tumor is completely removed. Once the Mohs surgeon has completely removed your skin cancer through Mohs surgery, reconstruction for optimizing the final functional and cosmetic result becomes the highest priority. Generally, a post-surgical scar improves with time and can take over a year to fully mature. As your surgical site heals, new blood vessels can appear and support the healing changes occurring underneath the skin. This can result in the reddish appearance of the scar. This change is temporary and will improve with time.

In addition, the normal healing process involves a period of skin contraction, which often peaks 4 to 6 weeks after the surgery. This may appear as a bumpiness or hardening of the scar. On the face, this change is nearly always temporary and the scar will soften and improve with time. Your Mohs surgeon is available for you throughout the healing process to discuss any concerns that may arise.

Because of Mohs surgery’s high success rate, most patients require only a single surgery. This surgery usually includes repair of the wound as well. Other methods might require additional surgeries and pathology readings in order to repair the wound and to treat the cancer if it is not completely removed. Each of these additional surgeries and pathology readings require separate fees, while a single Mohs surgery procedure includes all of these into one fee.


1. Holmkvist, Kristina A., MD, Rogers, Gary S., MD and Dahl, Patrick R., MD, “Incidence of residual basal cell carcinoma in patients who appear tumor free after biopsy,” Journal of the American Academy of Dermatology, 1999 October, Volume 41, Issue 4, pages 600-605.

2. Alcalay, J., MD and Alkalay, R., MD, “Histological evaluation of residual basal cell carcinoma after shave biopsy prior to Mohs micrographic surgery,” Journal of the European Academy of Dermatology and Venereology, no. doi: 10.1111/j.1468-3083.2010.03881.x

American_Academy_of_Dermatology Logo
American Board of Dermatology Logo
National Naval Medical Center Logo