What is Mohs surgery?

Mohs surgery is a very precise form of microsurgery developed to remove common forms of skin cancer.  Also known as chemosurgery, the technique was invented in 1938 by Dr.  Frederic E. Mohs, a very famous American surgeon. 

The technique is very effective at removing skin cancers, having a cure rate of between 97% and 99% for the most common forms of skin cancer. It is particularly useful for removing Basal Cell Carcinomas (BCC) on the face because a minimal amount of tissue is removed during the procedure.

How is Mohs surgery performed?

The goal of Mohs surgery is to remove cancerous tissue with a minimal amount of impact on the surrounding healthy tissue.  This allows the surgeon to perform very precise cuts to excise the cancerous tissue.

After the tissue is removed, it is immediately tested for the presence of cancer cells.  This results will inform the surgeon if they need to remove additional tissue from the site of the tumour.  

Because the procedure is micrographically controlled and very precise, it reduces the impact of the surgery on healthy tissue surrounding the skin cancer.  It is also a fairly cost-effective form of surgery because it combines two steps (surgery and tissue analysis) while reducing the risk of the cancerous tissue remaining intact.

Mohs surgery can greatly reduce the amount of scarring and trauma from skin cancer removal.  It is ideal for locations on the body where tissue preservation is important, including the face, hands, genitals, and feet.

There are some limitations to Mohs surgery.  Because the procedure is time consuming, it is rarely used on non-melanoma mole removals that are on the trunk or upper legs.

There are four steps performed in Mohs surgical procedures:

  1. Surgically removing the tissue
  2. Mapping the tissue
    The tissue is frozen and cut into small pieces between 5 and 10 micrometers in size.  It is them stained with hematoxylin and eosin (H&E) or other stains.
  3. The tissue is then examined to determine the presence of cancer cells.  If cancer cells are found in the sample more tissue may be removed.
  4. Reconstruction of the surgical defect

The procedure can be performed in a physician’s office under local anaesthetic.  The area surrounding the skin cancer is sterilised and anaesthetised before the physician makes the initial cut with a scalpel.  The cut very close to the site of the skin cancer — usually within 1 to 1.5 millimetres. 

The section of tissue is removed and processed (marked, divided, frozen, placed on slides and stained).  The tissue is read by a Mohs surgeon or pathologist who looks for cancerous cells.  If cancerous tissues found, they mark the section on the tissue map (a drawing of the skin cancer) and the surgeon performs another incision.  Once the cancerous tissue is completely removed, the surgeon usually repairs the affected area using standard cosmetic surgery techniques.

What is Mohs micrographic surgery?

Instead of looking at a frozen section of tissue, Mohs micrographic surgery analyses fresh tissue from the patient. In this type of surgery, the edges of the proposed incision are tested for the presence of cancer cells.  This helps the physician to make a precise first cut. 

They will then remove a thin layer of tissue, which is immediately tested.  If cancerous cells are found at the edges or bottom of the sample, the physician will remove more tissue.  The procedure continues until no more cancerous cells are found.  Once the cancerous cells have been removed, the defect is repaired with traditional cosmetic surgery techniques.

How effective is Mohs surgery?

Studies have found that Mohs surgery has a cure rate of between 97% and 99.8% for basal cell carcinomas, the most common form of skin cancer.   Recurrent basal cell cancer has a 94% cure rate, melanoma-in-situ has a cure rate of between 77% and 98% depending on the surgeon, while other forms of melanoma have a cure rate of approximately 52%.

Because the tissue is so precisely removed, there is much less risk of scarring and damage to the skin.  When performed by a skilled surgeon, patients usually have an excellent cosmetic outcome.