Mohs Surgery

  • Medical Author:
    Gary W. Cole, MD, FAAD

    Dr. Cole is board certified in dermatology. He obtained his BA degree in bacteriology, his MA degree in microbiology, and his MD at the University of California, Los Angeles. He trained in dermatology at the University of Oregon, where he completed his residency.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Skin Cancer Treatment

There are several effective means of treating skin cancer. The choice of therapy depends on the location and size of the tumor, the microscopic characteristics of the cancer, and the general health of the patient.

  • Destruction by electrodessication and curettage (EDC)
  • Surgical excision
  • Mohs micrographic surgery
  • Radiation therapy

What is Mohs surgery?

Mohs surgery, also referred to as Mohs micrographic surgery (MMS), is a special technique that utilizes a both pathology and surgery to remove skin cancers in a physician’s office. Mohs is a very precise, highly detailed method whereby horizontal pieces of tissue are cut from the bottom-most layer layers of the skin tumor and immediately stained and examined under the microscope. Repeated saucer-shaped layers of tissue are removed and examined until no more skin cancer can be microscopically visualized in the sample.

The procedure uses frozen sections of skin that are then stained with special dyes. The dyed frozen pieces of skin are examined under the microscope and a tumor map showing the sites of any residual cancer cells is drawn by the Mohs surgeon. The process permits an examination of the entire tumor’s margins simultaneously while the patient is waiting. If more cancer cells are seen under the microscope, tissue is removed at the site of involvement. Each skin layer that is removed is called a "level." If no more cancer cells are seen at a particular level, then it is deemed "clear" (no more tumor) and no additional levels are removed.

By removing only tissue where cancer is known to be present, the technique combines a very high cure rate with excellent preservation of normal skin. Once the cancer has been fully removed, the surgeon will determine the type of repair for the best cosmetic result. The surgeon may refer patients to another physician for wound closure, may close the wound immediately, or may let the wound heal on its own.

MMS is special because the entire edge and under-surface of each skin cancer layer is microscopically examined for the presence of cancer cells. Traditional surgical pathology techniques uses vertical sections (bread loafing) and is only helpful to evaluate 1%-3% of the tumor margins, thereby increasing the chances that a small tumor cluster maybe missed and left behind. MMS enables the examination of 100% of the entire tumor's margin, thereby reducing the chance of recurrence of the skin cancer.

MMS surgery is significantly more labor intensive than conventional methods of treating skin cancers, and as a result, it is more expensive. This type of surgery is typically reserved only for certain situations, which include recurrent cancers that have not been cured by conventional techniques, large tumors with indistinct margins, tumors that occur in cosmetically sensitive areas like the mid-facial tissues, and scarring basal cell cancers, which are known to have a high recurrence rate.

MMS is scheduled with the understanding that the patient may be spending the entire day in the office depending on the number of levels necessary to clear the tumor. Most of these procedures are performed with the patient in the waiting room awaiting the verdict from the Mohs surgeon.

Medically Reviewed by a Doctor on 6/3/2016

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