Mohs micrographic surgery information

What is Mohs surgery?

Mohs micrographic surgery is a highly effective and advanced treatment for skin cancer. It offers the highest potential for cure (up to 99%) because the tumour is precisely removed and analysed layer by layer under the microscope during your appointment, and prior to reconstruction of the wound. Your surgeon is also the pathologist providing a powerful and effective combination to accurately remove the skin cancer cells. An important additional benefit is its ability to minimise the removal of normal tissue surrounding the tumour, leading to a smaller defect and a superior cosmetic outcome.

The term "Mohs surgery" is derived from its founder and creator, Dr Frederic Mohs, MD.  He was a professor of surgery at the University of Wisconsin when he started developing the technique right back in the 1930s.  Since that time, it has undergone many refinements to make the procedure more rapid and comfortable, but the name has been retained in his honour.

How does it differ from traditional surgery?

The visible part of a skin cancer is very often only the "tip of the iceberg".  So-called thin roots of cancer cells unseen by the naked eye, may spread deep and wide and only be visible to examination under a microscope.

With traditional surgery, the tumour is removed along with a moderate margin of normal surrounding tissue. The wound is then closed prior to microscopic evaluation of the tumour or its distance from the edge of the wound. The tissue is sent to the laboratory for a sampling technique referred to as "bread-loafing" where a small number of very thin samples (cross-sections) of tissue are analysed. This technique usually results in less than 1% of peripheral margin of the specimen being evaluated and can miss the roots of the skin cancer. This is usually adequate for areas of the body where a large margin of normal tissue can be taken, increasing the chances the whole tumour is removed.

However, for tumours involving the face, head, and neck, it is crucial all tumour cells are removed with the highest accuracy, without sacrificing unnecessary normal tissue which can significantly worsen the cosmetic result. In this situation traditional surgery suffers from two major disadvantages: 

• Tumour cells may remain - if this is detected in microscopic sampling, repeat surgery will be required. If the sampling fails to detect persistent tumour, these cells are left to continue their growth and spread, often masked by the surgical scar.

• More than necessary normal surrounding tissue may be removed as part of the 'safety margin'

• By aiming to evaluate 100% of the surgical margin, it provides the highest assurance that all the cancer cells are removed during surgery
• The amount of normal tissue loss is minimised
• As a result, the functional and cosmetic outcome can be maximised
• The pathology (microscopic evaluation) is performed on the day by your Mohs surgeon, so there is no waiting for results following surgery
• The surgical repair of the site is performed on the same day, in the majority of cases
• It can cure skin cancers where other methods have failed

Author: 


Dr Todd Gunson MBChB FRACP FACD FACMS FNZDS

Auckland Dermatologist and Mohs surgeon