Developed by Frederic E. Mohs, M.D. at the University of Wisconsin in the 1930s, Mohs Micrographic Surgery for the removal of skin cancer is a highly precise, highly effective method that excises not only the visible tumor but also any "roots" that may have extended beneath the skin surface into blood vessels, nerves, cartilage or scar tissue from previous surgery. Five-year cure rates have been demonstrated up to 99 percent for first-treatment cancers and 95 percent for recurring cancers.
Mohs surgery involves the systematic removal and microscopic analysis of thin layers of skin at the tumor site until the last traces of cancerous tissue have been eliminated. The immediate and complete microscopic examination and evaluation of excised tissue is what differentiates Mohs surgery from other cancer removal procedures. Only cancerous tissue is removed, minimizing both post-operative wound size and the chance of regrowth.
Mohs surgery is not appropriate for all types of cancer. It is most commonly used for basal and squamous cell carcinomas, although it can be recommended for the eradication of other cancers such as melanoma. Cancers that are likely to recur or have already recurred are often treated using this technique because it is so thorough. Additionally, high precision makes Mohs surgery ideal for the elimination of cancers in cosmetically and functionally critical areas such as the face (nose, eyelids, lips, hairline), hands, feet and genitals.
Because they function as surgeon, pathologist and reconstructive surgeon during the cancer removal process, Mohs physicians must be highly trained in dermatology, dermatologic surgery, dermatopathology and Mohs surgery. They work in offices equipped with appropriate surgical and laboratory facilities, and are supported by Mohs-trained nursing and histotechnological staff. Excised tissue is examined in the same location where surgery is performed, so the entire process can be completed in a single day, inclusive of minor wound repair.
Patients undergoing surgery are given a local anesthetic and remain awake; most experience little or no discomfort. In the first stage, which lasts only a few minutes, the visible cancer is removed along with an additional thin layer of tissue. This sample is then cut, stained, and marked on a diagram known as a Mohs map. It is then frozen. Over the next hour or so, a technician examines thin slices of this sample under a microscope, looking for evidence of cancerous tissue.
If cancerous tissue is found within the sample, the surgeon removes another thin layer of skin from the patient only in the area where the abnormal cells were located . This may be only a fraction of the size of the original site. The steps described above are repeated until all evidence of cancer has been eliminated. On average three or fewer stages are necessary, with the entire procedure lasting under four hours.
The final step in the Mohs procedure is wound repair or reconstruction. Options for post-surgical repair vary depending on the extent of the wound and include letting the wound heal naturally; closing the wound with sutures, skin flaps or skin grafts; or more extensive plastic or reconstructive surgery. Whatever procedure is chosen may be performed by the Mohs surgeon, the original referring physician or another physician. Scar revision is possible later on with tissue fillers, dermabrasion, chemical peels, laser resurfacing or other methods.
Because much of the time is spent waiting, patients are urged to bring a book or something else to occupy the time in between procedures. It is also recommended that another person accompany the patient for emotional support and to drive home afterwards.
As with any surgery, there are risks. Tiny nerve endings at the tumor site are cut and may produce temporary or permanent numbness in the area. When tumors are large or cancers extend deep into the tissue, it may be necessary to cut a nerve that controls muscles, leading to temporary or permanent weakness. This is unusual, however. Other complications may include tenderness, itching, shooting pains, and need for further surgery if skin flaps or grafts fail.
For more information, visit the American College of Mohs Micrographic Surgery and Cutaneous Oncology at mohscollege.org.