Mohs micrographic surgery

What is skin cancer?

Cancer is the abnormal growth of cells at an uncontrolled and unpredictable rate. The cancer tissue usually grows at the expense of surrounding normal tissue. In the skin, the most common types of cancer are basal cell carcinoma and squamous cell carcinoma. The names reflect the cell within the skin from which the particular type of skin cancer originates. Malignant melanoma or a "cancerous mole" is a rarer type of skin cancer that usually appears as a dark colored spot or bump on your skin and slowly enlarges. In the Mohs surgery unit, we treat basal cell carcinomas, squamous cell carcinomas, malignant melanoma and other unusual skin tumors.

What are basal cell and squamous cell carcinomas?

Both of these cancers behave and are treated similarly. The difference lies in the cell from which it originates within the skin. Often, this can only be distinguished by examining the skin under a microscope. Basal cell carcinoma is the most common cancer of any type with over 1,000,000 new cases a year. Both basal and squamous cell carcinoma most commonly occur on the head and neck. The carcinoma often begins as a small bump that can look like a pimple but will continue to enlarge, often bleeds, and does not heal completely. It may be red, flesh-colored or darker than the surrounding skin. Basal cell carcinoma rarely spreads (metastasizes) to distant parts of the body. Instead, it grows larger and deeper, destroying nearby parts of the body in its path. Squamous cell carcinoma behaves locally like basal cell carcinoma. However, certain tumors can metastasize (spread elsewhere) from the skin. This will be discussed with you prior to surgery.

The abnormal growth (cancer) originates in the uppermost layer of the skin. The cancer then grows downward, forming root and fingerlike projections under the surface of the skin. Unfortunately, at times these roots are so subtle they cannot be seen without the aid of a microscope. Therefore, what you see on your skin is sometimes only a small portion of the total tumor. There are several different types of basal and squamous cell carcinoma. It is important to distinguish these types prior to treatment, as different therapies may be required. For this reason a biopsy is usually performed to treatment.

The most common association with skin cancer is long-term exposure to sunlight. This is why skin cancers develop most often on the face and the arms (sun-exposed body parts). They occur more commonly in fair-skinned people than dark-skinned people, and in the United States they are found most frequently in the southern (sun-belt) areas. Superficial x-rays, which were used many years ago for treatment of certain skin diseases, may result in skin cancer many years later. Trauma (scars), certain chemicals and rare inherited diseases may also contribute to the development of skin cancer.

What about melanoma?

Melanoma is the deadliest skin cancer accounting for two-thirds of all deaths attributed to skin cancers. The standard treatment for melanoma is surgical removal of the melanoma and a wide area of normal appearing skin surrounding the melanoma. There are, however, special cases, especially on the head and neck region, where Mohs micrographic surgery is beneficial in the treatment of melanoma. Many of the melanomas in this region have poorly defined borders making standard excision difficult.

Mohs surgery in the treatment of melanoma is modified. The initial stages done by frozen sectioning is the same as for other skin cancers. At the conclusion of the standard Mohs surgery, however, an additional rim of tissue is removed for additional histological examination that can take a few days to process. This additional step allows for a more precise treatment of the melanoma. Accordingly, the reconstruction will be delayed until this final rim of tissue is cancer free.

How successful is the treatment of skin cancer?

Initial treatment of skin cancers has a success rate greater than 90 percent. Methods commonly employed to treat skin cancer include excision (surgical removal and stitching); curettage and electrodesication (scraping and burning with an electric needle); cryosurgery (freezing); and radiation therapy ("deep x-ray"). The method chosen depends upon several factors, such as the microscopic type of tumor, the location and size of the cancer and previous therapy. You may have had one or more of these methods of treatment before coming for Mohs surgery.

If a skin cancer previously treated by one of the above techniques recurs (comes back), retreating using these methods has a success rate of less than 75 percent. The success rate for Mohs surgery, even in treating recurrent lesions, is about 97-98 percent. Mohs surgery (discussed in detail later) is very time consuming and requires a highly trained team of medical personnel. The vast majority of Mohs surgeons are dermatologists who have had extensive fellowship training after completing their dermatology training. At OHSU all Mohs surgeons are fellowship trained and members of the American College of Mohs Microsurgery and Cutaneous Oncology. Many skin cancers that are easily and effectively treated by the other methods listed previously do not require Mohs surgery. Mohs surgery is reserved for recurrent skin cancers or for primary skin cancers that are difficult to treat initially with other therapies.

What is Mohs surgery?

In the early 1940s, Dr. Frederic Mohs, professor of surgery at the University of Wisconsin, developed a form of treatment for skin cancers he called chemosurgery. "Chemosurgery" is derived from the words "chemical" and "surgery". The addition of "Mohs" honors the doctor who developed the technique. It is a highly specialized form of treatment for the total removal of skin cancers. It is performed by a team of medical personnel that includes physicians, nurses and technicians. The physician heading the team has subspecialty (fellowship) surgical training in the technique and is recognized by the American College of Mohs Micrographic Surgery and Cutaneous Oncology. Other physicians on the team include fellows and residents who will help assist while learning the technique. The nurse is an important part of the team who helps answer your questions, respond to your anxieties, assist in surgery and instruct you in dressing and wound care after the surgery is performed. A technician performs the important task of preparing the tissue slides, which are examined under a microscope by the physician.

The word "chemosurgery" when used today is really a misnomer. When Dr. Mohs initially introduced the procedure, he applied a chemical (zinc chloride) to the tumor and surrounding skin, which fixed the tissue prior to its removal. Since 1974, the procedure has been refined and improved upon so the vast majority of cases are done using fresh tissue (omitting the chemical paste).

Although the official name for the procedure is Mohs micrographic surgery, we prefer the shortened version of Mohs surgery. The surgery is performed as follows. The skin suspected of cancer is treated with a local anesthetic so there is no pain in the area. To remove most of the visible skin cancer, the tumor is scraped using a sharp instrument called a curette. A disc-shaped piece of tissue is then removed with a scalpel around and underneath the scraped skin and carefully divided into pieces that will fit on a microscope slide. The edges are marked with colored dyes; a careful map or diagram of the tissue is made; and the tissue is submitted for frozen section processing. Most bleeding is controlled using pressure and electrocautery, although occasionally a small blood vessel is encountered that must be tied using suture material. A pressure dressing is then applied, and the patient is asked to wait while the slides are being processed. The surgeon will then examine the slides under the microscope and be able to tell if any tumor is still present. If cancer cells remain, they can be located by referring to the map. Another section of tissue is then removed, and the procedure is repeated until the physician is satisfied that the entire base and sides of the wound have no cancer cells remaining. As well as ensuring total removal of the cancer, this process preserves as much normal, healthy surrounding skin as possible.

The removal and processing of each layer of tissue takes approximately one hour. Only 20 to 30 minutes of that are spent in the actual surgical procedure. The remaining time is required for slide preparation and interpretation. It usually takes two or three stages to complete the surgery. Therefore, by beginning early in the morning, Mohs surgery is generally finished in one day. Sometimes, however, a tumor may be extensive enough to necessitate continuing surgery a second day.

At the end of Mohs surgery, you will be left with a surgical wound. Several reconstruction options will be discussed with you in order to provide the best possible cosmetic results and is usually performed on the same day.

The possibilities include:
  • Healing by granulation involves letting the wound heal by itself. Experience has taught us that there are certain areas of the body where nature will heal a wound as nicely as any further surgical procedures. There are also times when a wound will be left to heal knowing that if the resultant scar is unacceptable, some form of reconstructive surgery can be performed at a later date.

  • Closing the wound with stitches is often performed on small to medium size wounds. This involves some adjustment of the wound and sewing the skin edges together with a combination of deep and superficial sutures. This procedure speeds healing and can offer a good cosmetic result. For example, the scar can lie along a wrinkle line. However, the scar line may be longer than what you may have expected.

  • Skin grafts involve covering a surgery site with skin from another area of the body. There are two types of skin grafts. The first is called a split-thickness graft. This is a thin shave of skin, usually taken from the thigh, which is used to cover a surgical wound. This can be either a permanent coverage or temporary coverage before another cosmetic procedure is done at a later date. The second graft type is the full-thickness graft. This graft requires a thicker layer of skin to achieve proper results. In this instance, skin is usually removed from around the area or distant site, (the donor site) and stitched to cover a wound. The donor site then is sutured together to provide a good cosmetic result.

  • Skin flaps involve movement of adjacent, healthy tissue to cover a surgical site. Where practical, they are chosen because of the excellent cosmetic match of nearby skin.
In summary, by microscopically pinpointing affected areas and removing these tissues, the Mohs surgeon can successfully remove your skin cancer. Because normal tissue is preserved to the greatest extent possible, the Mohs surgeon is able to offer you the possibility of a good cosmetic result. Although an attempt will be made to minimize the scar, you will be left with a scar of some kind.

Read about Preparing for Surgery.