Mohs micrographic surgery (Mohs surgery) is named after Dr Frederic E Mohs who invented this technique in the 1930s. The technique for Mohs surgery has been revised over the years and is globally the gold standard treatment for skin cancers. Compared to traditional wide excision surgery, Mohs surgery delivers a higher rate of removing all cancer cells and preventing cancer recurrence, while keeping the wound as small as possible. A smaller wound allows faster healing and results in a smaller scar. Mohs micrographic surgery is the recommended treatment for skin cancers on the face (where most skin cancers arise), for large skin cancers and cancers on areas where tissue preservation is critical, such as the genitals, hands and feet.

Mohs micrographic surgery are mostly performed by fellowship-trained dermatological surgeons. In Mohs surgery, cancer tissue is removed layer by layer and examined under the microscope on the same day. Further tissue is only removed if remaining cancer cells are seen. This means healthy, cancer-free tissue is not sacrificed. After the doctor is satisfied that no more cancer cells are seen, the wound can be closed. The dermatologic surgeon is also trained to perform reconstruction of the wound, using various methods such as the skin flaps or grafts.

Mohs micrographic surgery is usually performed under local anaesthesia. Fasting is not required. The doctor will have gone through the patient's medications and advised which may be continued on the day of surgery. The visible skin cancer is marked out and removed; this is the first layer of Mohs surgery. This tissue is immediately sent to an attached lab and processed. This procedure involves sectioning, staining and mounting tissue onto microscope slides, and may take up to 2 hours depending on the size and thickness of the tissue. Meanwhile, the wound is dressed, and the patient may leave the operating room and wait at the adjoining waiting area with family members and have refreshments.

After the tissue is prepared, the dermatologic surgeon will look at the slides personally to check if all cancer cells from the patient have been removed. If there are still cancer cells seen, the patient will be brought back to the operating room for a bit more skin tissue to be removed. This process of tissue removal and testing is repeated until the doctor is satisfied that no more cancer cells remain. Each cycle is called a Mohs stage, and the majority of Mohs surgeries can be completed within 3 stages.

After cancer clearance is complete, the dermatologic surgeon will discuss with the patient the best form of reconstruction. Small wounds may be closed by stitching up the wound or by letting it heal naturally. Larger wounds may be closed using a skin graft or flap, and will be performed by the dermatologic surgeon on the same day.

Mohs micrographic surgery is usually performed for skin cancers on cosmetically sensitive areas such as the face, and where the risk of cancer recurrence is high. Examples where Mohs surgery is recommended include:

1. Skin cancers on the face, rest of the head and neck, hands, feet and genitalia.
2. Skin cancers that are large, deep or have ill-defined borders.
3. Cancers which show aggressive features on biopsy.
4. Recurrent skin cancers (ie. have recurred after previous treatment).
5. Patients with lower immunity eg. on medications that suppress the immune system

Mohs surgery is generally considered a low-risk procedure. Similar to other skin surgeries, there is a small risk of bleeding, infection, and pain after the anaesthesia wears off. The doctor will prescribe painkillers if these are required. On the face, there are also small nerves that run underneath the skin and depending on the location and depth of the tumour, these nerves may be affected during removal of the tumour. The doctor will advise you of this risk if it is relevant.

The same risks are present for all skin surgeries. Generally, because the amount of tissue removed in Mohs surgery is less than traditional wide excision surgery, these risks are comparatively lower.