What is Mohs Surgery?


Mohs micrographic surgery has the highest cure rate for basal cell and squamous cell carcinomas and is the treatment of choice for locally recurrent skin cancers, with typical cure rates of 95 to 97 percent, while other methods used to treat local recurrences achieve a typical cure rate of only 50 to 60 percent.

The advantage of Mohs surgery is its precision and the ability to remove the entire cancer while only removing a minimum amount of healthy tissue. To accomplish this, the physician removes a thin layer of tissue which is then carefully examined for for malignant cells. This process is sytematically repeated until all areas of tissue are tumor-free.

An alternative method of cancer tissue removal involves excision of the entire tumor and a large area of normal-appearing tissue around it to ensure that all traces of the tumor are removed. The Mohs technique has several significant advantages over the alternative technique. It preserves more healthy tissue than any other cancer surgery technique while enabling the physician to eliminate all visible areas of the tumor.

After examining the tissue under a microscope,the Mohs surgeon knows the exact extent of the tumor. Because of this precision, Mohs surgery is an excellent technique for removing skin cancers in the areas around the eyes, nose, ears and mouth.

Another advantage of Mohs surgery is that it does not require general anesthesia, allowing patients who are poor candidates for conventional surgery to be successfully treated. The surgery can usually be completed in half a day or less, and most patients can be treated on an outpatient basis.

Usually, the physician closes the wound immediately after successful removal of all cancerous tissue. However, in some cases the wound is allowed to heal by itself without suturing, depending on the location, size, and depth of the wound site. The healing process typically takes about four to eight weeks, and the remaining scar can be corrected at a later date, if necessary. Patients return to our office in about 1-2 weeks for a re-check to ensure the wound is healing properly.

  • What is Mohs micrographic Surgery (MMS)?

Mohs micrographic surgery is a minor surgical procedure and special method of removing skin cancers using local anesthesia (numbing). The majority of cases are performed right in the physician’s office. Mohs is a very precise, highly detailed technique whereby small layers of skin are removed and immediately examined under the microscope to make sure the skin cancer is completely removed.

The procedure uses frozen sections of skin which are then stained with special dyes. The dyed frozen pieces of skin are further examined under the microscope and a tumor map is drawn by the Mohs surgeon. The freezing process allows an immediate examination of the entire tumor margin and tissue histology (microscopic examination of cells).

If more cancer cells or “roots” are seen under the microscope, then another skin layer is removed and again examined. Each time that a skin level is removed, it is called a “level”. If no more cancer roots are seen, then it is called “clear” (no more tumor) and no additional levels are needed.

By removing only tissue where cancer is known to be present, the technique combines a very high cure rate with good preservation of normal skin. Once the cancer has been fully removed, the Mohs surgeon looks at the wound to determine the way to get the best wound repair and cosmetic result for you.

Mohs is special because the entire edge and undersurface of each skin cancer layer is carefully examined under the microscope for the presence of very small cancer cells. With regular or traditional surgery only about 1 to 3% of the tumor margins are actually examined thereby increasing the chances that a small tumor root would be missed and left behind. Mohs allows for examination of 100% of the tumor margins thereby reducing the chance that tumor cells will be left behind.

Mohs is usually scheduled only on certain days in the doctor’s office because of the required equipment, tissue stains (dye), Mohs technologists, and microscopes. Most of these procedures are generally performed with the patient waiting in the office for the tissue to be “read” or interpreted by the Mohs surgeon.

  • Where can I have Mohs Surgery?

Mohs micrographic surgery is usually performed in an outpatient setting like a doctor’s office and under local anesthetic (lidocaine). Sometimes the procedure may be performed in an outpatient surgical center with the assistance of an anesthesiologist. Rarely, it is performed in an inpatient hospital setting.

  • How long does the surgery take?

You are generally in the medical office for several hours( average 2-7 hours) on the day of your Mohs procedure. Depending on how large or difficult your skin cancer is, different numbers of levels may be required to achieve clearance. Mohs requires your patience and your doctor’s careful effort and skill. It is not always possible to predict ahead of time how many hours your specific procedure will take. Most patients leave their day’s schedule open to allow for adequate time to complete their Mohs.

  • What kind of physician can perform Mohs Surgery?

Most Mohs surgeons are specially trained dermatologists. There are also some plastic surgery, or Ear , Nose and Throat (ENT) surgeons who are trained and may also perform Mohs.

  • Where can I find a doctor board certified in Mohs?

There is no current Board Certification for Mohs Surgery. There are two nationally recognized and respected national Mohs specialty groups called the American College of Mohs Surgery and the American Society for Mohs Surgery (ASMS).

Both of these medical groups have specialty training and certification exams for their members. Members of The American College of Mohs Surgery usually have completed an additional 1 to 2 years of Mohs training. Members of the American Society for Mohs Surgery are also trained and required to actively participate in an annual quality control Mohs slide peer review.

  • Is Mohs only for skin cancer?

Yes, Mohs is a widely used method of surgically removing the most common types of skin cancers including basal cell carcinoma and squamous cell carcinoma. It is currently not used to remove non-cancerous growths.

Less frequently, Mohs may also be used for other malignant tumors. In special cases, Mohs may be used to surgically treat malignant melanoma, lentigo maligna, dermatofirosarcoma protuberans, merkel cell tumor, microcystic adnexal carcinoma, malignant trichoepithelioma, angiosarcoma, atypical fibroxanthoma and other cancerous tumors. However, most Mohs surgeons treat primarily basal and squamous cell cancers by this technique.

  • Can I remove my moles using Mohs?

No, Mohs is usually not for mole removal. It is primarily designed for removing skin cancers. Moles are usually removed by standard or traditional surgery.

  • Am I a good candidate for Mohs Surgery?

You may not be a good candidate for Mohs if you are unable to tolerate local anesthesia, have extreme anxiety, have a surgical phobia, or are in very poor health.

Your decision on the best treatment choice may depend on different factors such as the location and type of skin cancer, your past treatments, your overall health, and level of comfort. Your physician can help you sort through the different treatments and assist in your shared decision making process. However, the right decision for you is always yours and your doctor’s to make.

Article by
Orange County Dermatologist