Mohs surgery, also called Mohs micrographic surgery, is a precise surgical technique that is used to remove all parts of cancerous skin tumors, while preserving as much healthy tissue as possible.
Mohs surgery is used to treat such cancers of the skin as basal cell carcinoma, squamous cell carcinoma, and melanoma.
Malignant skin tumors may occur in strange, asymmetrical shapes. The tumor may have long finger-like projections that extend across the skin (laterally) or down into the skin. Because these extensions may be composed of only a few cells, they cannot be seen or felt. Standard surgical removal (excision) may miss these cancerous cells leading to recurrence of the tumor. To assure removal of all cancerous tissue, a large piece of skin needs to be removed. This causes a cosmetically unacceptable result, especially if the cancer is located on the face. Mohs surgery enables the surgeon to precisely excise the entire tumor without removing excessive amounts of the surrounding healthy tissue.
Mohs surgery is performed when:
According to the National Cancer Institute (NCI), about one million people in the United States are diagnosed with skin cancer every year. The two most common types of skin cancer are basal cell carcinoma and squamous cell carcinoma, with basal cell carcinoma accounting for more than 90% of all of skin cancers.
Melanoma is the most serious type of skin cancer. Each year in the United States more than 53,600 people are diagnosed with melanoma, and it is becoming more and more common, especially among Western countries. In the United States, the percentage of people who develop melanoma has more than doubled in the past 30 years.
There are two types of Mohs surgery: fresh-tissue technique and fixed-tissue technique. Of the surgeons who perform Mohs surgery, 72% use only the fresh-tissue technique. The remaining surgeons (18%) use both techniques. However, the fixed-tissue technique is used in fewer than 5% of patients. The main difference between the two techniques is in the preparatory steps.
Fresh-tissue Mohs surgery is performed under local anesthesia for tumors of the skin. The area to be excised is cleaned with a disinfectant solution and a sterile drape is placed over the site. The surgeon may outline the tumor using a surgical marking pen, or a dye. A local anesthetic (lidocaine plus epinephrine) is injected into the area. Once the local anesthetic has taken effect, the main portion of the tumor is excised (debulked) using a spoon-shaped tool (curette). To define the area to be excised and to allow for accurate mapping of the tumor, the surgeon makes identifying marks around the lesion. These marks may be made with stitches, staples, fine cuts with a scalpel, or temporary tattoos. One layer of tissue is carefully excised (first Mohs excision), cut into smaller sections, and taken to the laboratory for analysis.
If cancerous cells are found in any of the tissue sections, a second layer of tissue is removed (second Mohs excision). Because only the sections that have cancerous cells are removed, healthy tissue can be spared. The entire procedure, including surgical repair of the wound, is performed in one day. Surgical repair may be performed by the Mohs surgeon, a plastic surgeon, or another specialist. In certain cases, wounds may be allowed to heal naturally.
With fixed-tissue Mohs surgery, the tumor is debulked, as described previously. Trichloracetic acid is applied to the wound to control bleeding, followed by a preservative (fixative) called zinc chloride. The wound is dressed and the tissue is allowed to fix for six to 24 hours, depending on the depth of the tissue involved. This period, called the fixation period, can be painful to the patient. The first Mohs excision is performed as described; however, anesthesia is not required because the tissue is dead. If cancerous cells are found, fixative is applied to the affected area for an additional six to 24 hours. Excisions are performed in this sequential process until all cancerous tissue is removed. Surgical repair of the wound may be performed once all fixed tissue has sloughed off—usually a few days after the last excision.
An oncologist will have diagnosed the skin cancer of the patient using such standard cancer diagnostic tools as biopsy of the tumor.
To prepare for surgery, and under certain conditions (such as the location of the skin tumor or health status of the patient), antibiotics may be given to the patient prior to the procedure; this is known as prophylactic antibiotic treatment. Patients are encouraged to eat prior to surgery and also to bring along snacks in case the procedure become lengthy. To reduce the risk of bleeding, the use of nonsteroidal anti-inflammatory drugs (NSAIDs), alcohol, vitamin E, and fish oil tablets should be avoided prior to the procedure. The patient who uses over-thecounter aspirin or the prescription blood-thinners, brands Coumadin (warfarin, generically) and heparin should consult with the prescribing physician before adjusting the dosage of any drug.
Patients should expect to receive specific wound care instructions from their physician or surgeon. Generally, however, wounds that have been repaired with absorbable stitches or skin grafts should be kept covered with a bandage for one week. Wounds that have been repaired using nonabsorbable stitches should also be covered with a bandage that should be replaced daily until the stitches are removed one to two weeks later. Signs of infection (e.g., redness, pain, drainage) should be reported to the physician immediately.
Using the fresh-tissue technique on a large tumor requires large amounts of local anesthetic that can be toxic. Complications of Mohs surgery include infection, bleeding, scarring, and nerve damage.
Tumors spread in unpredictable patterns. Sometimes a seemingly small tumor is found to be quite large and widespread, resulting in a much larger excision than was anticipated.
Most skin cancers treated by Mohs surgery are completely removed with minimal loss of normal skin.
Mohs surgery provides high cure rates for malignant skin tumors. For instance, the five-year cure rate for basal cell carcinoma treated by Mohs surgery is higher than 99%. The frequency of recurrence is much lower with Mohs surgery is much lower than with conventional surgical excision—less than 1%.
Mohs surgery is a specialized technique that is not indicated for the treatment of every type of skin cancer, and is most appropriately used under specific, well-defined circumstances. The majority of basal cell carcinomas can be treated with very high cure rates by standard methods, including electrodesiccation and curettage (ED&C), local excision, cryosurgery (freezing), and irradiation.
See also Cryotherapy .
Cook, J. L., and J. B. Perone. "A prospective evaluation of the incidence of complications associated with Mohs micrographic surgery." Archives of Dermatology 139 (February 2003): 143-152.
Jackson, E. M., and J. Cook. "Mohs micrographic surgery of a papillary eccrine adenoma." Dermatologic Surgery 28 (December 2002): 1168-1172.
Smeets, N. W., Stavast-Kooy, A. J., Krekels, G. A., Daemen, M. J., and H. A. Neumann. "Adjuvant Cytokeratin Staining in Mohs Micrographic Surgery for Basal Cell Carcinoma." Dermatologic Surgery 29 (April 2003): 375-377.
American Society for Mohs Surgery. Private Mail Box 391, 5901 Warner Avenue, Huntington Beach, CA 92649-4659. (714) 840-3065. (800) 616-ASMS (2767). http://www.mohssurgery.org .
"About Mohs Micrographic Surgery." Mohs College. http://www.mohscollege.org/AboutMMS.html .
Belinda Rowland, Ph.D.
Monique Laberge, Ph.D.
Mohs surgery is performed in a hospital setting by highly trained surgeons who are specialists both in dermatology and pathology. With their extensive knowledge of the skin and unique pathologic skills, they are able to remove only diseased tissue, preserving healthy tissue and minimizing the cosmetic impact of the surgery. Only physicians who have also completed a residency in dermatology are qualified for Mohs surgical training. The surgery is very often performed on an outpatient basis, usually in one day.