What is Mohs Microscopic Surgery?

Most effective and advanced

treatment for skin cancer today

The term “Mohs” refers to Dr. Frederic Mohs, Professor of Surgery at the University of Wisconsin, who developed this surgical technique in the 1930s. The technique has undergone many refinements and has come to be known as “Mohs micrographic surgery” or simply “Mohs surgery” in honor of Dr. Mohs


How does it work?

Step 1

The roots of a skin cancer may extend beyond the visible portion of a tumour. If these roots are not removed, the cancer will recur.

Step 2

The visible portion of the tumour is surgically removed

Step 3

A layer of skin is removed and divided into sections. The ACMS surgeon then colour-codes each of these sections with dyes and makes reference marks on the skin to show the source of these sections. A map of the surgical site is then drawn.

Step 4

The undersurface and edges of each section are microscopically examined for evidence of remaining cancer.

Step 5

If cancer cells are found under the microscope, the ACMS surgeon marks their location onto the “map” and returns to the patient to remove another layer of skin – but only from precisely where the cancel cells remain. The removal process stops when there is no longer any evidence of cancer remaining in the surgical site.

Why Mohs?

Mohs micrographic surgery is the most effective and advanced treatment for skin cancer today. It offers the highest potential for cure – even if the skin cancer has been previously treated by another method.

Originally developed in the 1930s, Mohs micrographic surgery has been refined into the most advanced, precise, and effective treatment for an increasing variety of skin cancer types. With the Mohs technique, physicians can precisely identify and remove an entire tumor while leaving the surrounding healthy tissue intact and unharmed.

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 the Mohs College surgeon 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%.

Benefits of Mohs

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 the Mohs surgeon, 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, virtually eliminating 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.

Preparation and Recovery

While treatment of your skin cancer is your primary concern, reconstruction of the treated area is also important. After your Mohs surgeon is confident that all of the cancer has been removed, together you will determine how the wound will be repaired. In addition to removing skin cancer, fellowship trained Mohs College surgeons have specialized reconstructive surgery training for repairing the wound.

Options for Reconstruction:
While your surgeon might be able to give you an idea of whether your reconstruction should take place immediately after surgery or be delayed until later, it’s impossible to know the extent of the cancer in advance.

After determining that the affected area is cancer free and reconstruction is necessary, the Mohs surgeon will review skin cancer reconstructive surgery options with you. Depending on the size of the tumor, depth of roots, and location, one of the following options will be selected:

  • Small, simple wounds may be allowed to heal by themselves (process known as secondary-intention healing)
  • Slightly larger wounds may be closed with stitches in a side-to-side fashion
  • Larger or more complicated wounds may require a skin graft from another area of the body or a flap, which closes the defect with skin adjacent to the wound
  • On rare occasions, the patient may be referred to another reconstructive surgical specialist

Post-Operative Management
Your surgeon will arrange post-surgical check-ups after Mohs surgery to monitor your recovery and spot any possible cancer recurrence as soon as possible. Since 2 out of 5 patients with one skin cancer will develop another within 5 years, follow-up is extremely important for early detection of any new lesions.