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 by your surgeon during your appointment, and prior to reconstruction of the wound. An important additional benefit is its ability to minimise the removal of normal tissue surrounding the tumour, leading to a smaller excision and a superior cosmetic outcome.  The surgical reconstruction of the wound is performed on-site in nearly all cases.

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 began developing the technique 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. Dr Gunson has completed fellowship training under the American College of Mohs surgery, the college set-up by Dr Mohs and his early colleagues.

Mohs surgery should not be confused with "surgery with frozen-section margin control". Mohs surgery utilises frozen section tissue processing to provide rapid histological sections for analysis at the time of surgery, but the difference lies in the way the tissue is cut in the laboratory. Surgery with frozen-section margin control utilises the standard "bread-loafing" technique described below. It allows rapid results but does not analyse the tissue in any more detail than standard surgery.

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 of the whole tumour being 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 compromise 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 initially masked by the surgical scar.
‣ More than necessary normal surrounding tissue may be removed as part of the ‘safety margin’
During Mohs surgery, your surgeon is also your pathologist who examines and interprets the tissue under the microscope. The direct involvement of your surgeon in every stage of the process allows for the highest degree of accuracy in orientation and analysis of the tissue, and is part of definition of Mohs surgery.

The Mohs surgery procedure

Mohs surgery is performed under local anaesthetic on-site at Auckland Skin & Cancer Foundation. Due to the processing time of your specimens, it may take 3-6 hours depending on the size and complexity. Most of this time however you are not required in the theatre, and can relax with a book, chat to a friend or relative, use your WiFi device, and enjoy light refreshments.

A dressing is applied to the wound after the first stage has been taken, and you will be informed as soon as your results are available. If tumour cells persist at any margin, a further stage will be taken and the new specimen analysed. Once the area is clear of tumour, you will return to theatre for surgical reconstruction. This may involve the use of a skin flap or skin graft. A final dressing is then applied, and you will be given detailed wound care instructions and an appointment for wound review and removal of sutures, usually six to seven days later.

Please visit the American College of Mohs Surgery website to read more about the surgery, including a step-by-step pictorial explanation of the process:


What are the advantages of Mohs surgery?

‣ 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 reconstruction (repair of the wound) is performed on-site at the time, without the need for general anaesthetic, in nearly all cases
‣ It can cure skin cancers where other methods have failed

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