Mohs surgery removes a tumour little by little in layers until no cancer remains, leaving as much healthy tissue as possible.
It is considered to be the most effective technique for treating many basel cell carcinomas (BCCs) and squamous cell carcinomas (SCCs), two of the most common types of skin cancer.
The Mohs procedure is micrographically controlled, it provides precise removal of the cancerous tissue, while healthy tissue is spared. It began as a technique called chemosurgery, developed by a doctor named Frederick Mohs in the late 1930s.
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What does this treatment do?
During Mohs surgery, thin horizontal layers of cancer-containing skin are gradually removed and examined until only cancer-free tissue remains.
Local anaesthetic is used to freeze the area. The surgeon uses a scalpel to remove the part of the tumour that can be seen along with a thin layer of tissue underneath.
The tissue sample is taken to the lab to be looked at under a microscope to see if there are any cancer cells still in the tissue. If there is cancer in the layer, another thin layer of tissue is removed and examined. Each round takes about an hour. The surgery takes up to 30 minutes and looking at the tissue under the microscope takes about the same time.
This process of removing a thin layer of skin and looking at it under a microscope continues until the surgeon no longer sees cancer cells and there is a surrounding margin of healthy tissue.
During Mohs surgery most patients remain awake. The procedure is done in stages, including lab work, while the patient waits. This allows all cancerous cells to be removed for the highest cure rate, sparing healthy tissue and leaving the smallest possible scar.
The technique is ideal for sites and situations where preserving as much normal tissue as possible is important such as tumours of the lips, ears and eyelids. Mohs surgery is also suited for skin cancers which are difficult or impossible to see with the naked eye, such as those that have come back after previous treatment.
By removing only tissue where cancer is present, the technique combines a very high cure rate with the excellent preservation of normal skin. After the cancer has been fully removed, the surgeon will determine the type of repair for the best cosmetic result.
Mohs surgery is significantly more labour intensive than conventional methods of skin cancer treatment and so is more expensive.