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Mohs Surgery

What Is Mohs Surgery?

Mohs surgery is a specialized type of surgery used to remove both common (ie, basal cell carcinoma, squamous cell carcinoma, melanoma) and rare skin cancers.

Mohs is the last name of the person who invented the technique: Frederic Mohs, MD. Mohs surgery is highly effective at removing skin cancer because the edges of the removed cancer tissue are checked much more thoroughly under the microscope than with regular surgery. In addition to being effective, the Mohs procedure allows the surgeon to leave behind normal skin and remove less healthy tissue.

Mohs surgery is not necessary for all skin cancers, but it is useful when:

  • The location of the skin cancer is near areas that are important for daily activities (like the fingers), or for appearance (like the nose)
  • Earlier treatments have not worked
  • A tumor is large
  • Regular surgery is less likely to remove the cancer

Success Rate of Mohs Surgery

The Mohs procedure involves surgically removing skin cancer layer by layer and examining the tissue under a microscope until healthy, cancer-free tissue around the tumor is reached (called clear margins). Because Dr. Petersen is specially trained as a cancer surgeon, pathologist, and reconstructive surgeon, Mohs surgery has the highest success rate of all treatments for skin cancer – up to 99%.

Following a biopsy, your skin cancer may no longer be visible. However, the surface lesion that was removed can 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. Mohs surgery removes these cancer “roots” and minimizes the chance of recurrence.

Advantages of Mohs Surgery

Mohs surgery is unique and so effective because of the way the removed tissue is microscopically examined, evaluating 100% of the surgical margins. The pathologic interpretation of the tissue margins is done on site by Dr. Petersen, who is specially trained in the reading of these slides and is best able to correlate any microscopic findings with the surgical site on the patient. Advantages of Mohs surgery include:

  • Ensuring complete cancer removal during surgery, minimizing the chance of the cancer growing back
  • Minimizing the amount of healthy tissue lost
  • Maximizing the functional and cosmetic outcome resulting from surgery
  • Repairing the site of the cancer the same day the cancer is removed, in most cases
  • Curing skin cancer when other methods have failed

Other skin cancer treatment methods blindly estimate the amount of tissue to treat, which can result in the unnecessary removal of healthy skin tissue and tumor re-growth if any cancer is missed.

What to Expect When Having Mohs Surgery

Mohs surgery is usually done with the patient awake. The tumor and the skin around it are numbed with injections of anesthesia. Dr. Petersen removes the skin cancer that can be seen with the naked eye and takes it to the laboratory on site. After the laboratory technician makes microscope slides with the removed skin cancer tissue, Dr. Petersen looks under the microscope to check for any cancer cells left along the edges of the tissue. Examining the tissue under the microscope can help detect cancer that is small, hidden, or deep under the skin. If more cancer is found, Dr. Petersen then removes more tissue along the sides or deep edge where the cancer is still present. This tissue is again processed by the laboratory and rechecked under the microscope by Dr. Petersen. The process continues until all of the cancer is cut out. Because it is not possible to know how many tries it will take to remove the entire tumor, patients should be prepared to be at the clinic for a minimum of four hours.

After all of the cancer is removed, the Dr. Petersen will discuss different ways to fix the wound. The wound can be left to heal on its own, can be stitched closed in a straight line, or may require a more complicated surgical procedure. Often the wound is closed the same day by Dr. Petersen, but sometimes it is repaired by another surgeon on the same day or a different day.

More information about how to prepare for your Mohs surgery appointment

More information about how to care for your surgical site after Mohs surgery

Mohs Surgery for Skin Cancer Diagram