Mohs Micrographic Surgery

In standard skin cancer surgery the tumour is removed with a fixed margin of normal skin, and the laboratory examines sample slices from the specimen, which shows only part of the edge. Mohs surgery takes a different approach. The surgeon removes the tumour with a narrow rim of tissue, cut at an angle, maps it and marks its orientation with coloured dyes. The tissue is then frozen and cut horizontally in the laboratory, so that the whole deep and outer edge appears on the slides. The Mohs surgeon, trained to read these slides, examines them and marks on the map exactly where any cancer remains. Only that part of the wound is cut out in the next stage. Because the edges are examined completely, Mohs surgery achieves high cure rates while keeping the wound as small as possible, which matters on the nose, eyelids, lips and ears. Most tumours are cleared in one to three stages.

Mohs surgery is not needed for every skin cancer; many small, well-defined cancers on the trunk or limbs are treated well with standard excision, scraping and cautery, creams or radiotherapy. It is recommended when keeping tissue matters or the risk of incomplete removal is higher. Typical indications are basal cell and squamous cell carcinomas on the central face, nose, eyelids, lips, ears, scalp, hands, feet and genitals; tumours with poorly defined edges; aggressive growth patterns under the microscope, such as infiltrative or morphoeic basal cell carcinoma; tumours that have come back after previous treatment; larger tumours; and cancers in people with weakened immune systems, such as organ transplant recipients. Mohs surgery can also be used for some rarer skin tumours, such as dermatofibrosarcoma protuberans, often with adapted laboratory methods. Melanoma is usually treated with standard wide excision, although modified Mohs techniques are used for some melanomas in situ on the face. A biopsy confirming the diagnosis is usually done beforehand.

You arrive in the morning, the site is marked and the skin is numbed with local anaesthetic, so you stay awake and comfortable. The surgeon removes the visible tumour and a thin layer of surrounding tissue, which takes about 15 to 30 minutes, and covers the wound with a temporary dressing. While the laboratory processes the tissue, which usually takes about an hour, you wait in a lounge area and can eat, drink and read. The surgeon then examines the slides. If cancer remains at any edge, you return to the procedure room, more anaesthetic is given if needed, and another thin layer is taken only from the affected area. This repeats until the edges are clear. The wound is then repaired: small wounds are stitched in a line, larger ones are closed with a local flap of nearby skin or a skin graft, and some heal on their own. Complex repairs near the eye or nose may be done by a plastic or eyelid surgeon the same or the next day.

Most people with a suitable skin cancer can have Mohs surgery, including older people and those with other medical conditions, because it uses only local anaesthesia. A biopsy report confirming the type of cancer is usually needed, and you should bring or send it with clear photographs of the site in advance. Blood thinners are often continued, since stopping them carries its own risk, but the team may ask for a recent blood test and advise you individually. Tell the team about pacemakers, artificial heart valves or joint replacements, and about any allergy to local anaesthetic. On the day, eat a normal breakfast, take your usual medicines unless told otherwise, wear comfortable clothes and bring something to read, as the day can be long. Arrange for someone to accompany you, especially if the wound is near the eye and swelling may affect your vision. International patients should plan at least a week, because of repair and stitch removal.

After surgery a pressure dressing is left for about 24 to 48 hours, and you are shown how to clean the wound and apply ointment. Discomfort is usually mild and settles with simple painkillers. Bruising and swelling are common, especially around the eyes after surgery on the nose or forehead, and they peak in the first few days. Keep your head raised, apply cold packs as instructed and avoid bending, heavy lifting and strenuous exercise for about one to two weeks. Facial stitches are usually removed after about five to seven days, and stitches elsewhere after up to two weeks. Plan to stay near the clinic for about a week so that the wound can be checked and stitches removed before flying. Flaps and grafts need protection from knocks and strong sun for several weeks. The scar is red at first and fades over about six to twelve months; massage and sun protection help.

Mohs surgery is safe and well tolerated, and serious complications are uncommon. Possible problems include bleeding from the wound, usually controlled with firm pressure, infection, which is treated with antibiotics, and slow healing of a flap or graft, particularly in smokers. Temporary or lasting numbness can occur around the scar, and rarely a small nerve that moves a facial muscle is affected when the tumour lies close to it. Scars are usually neat because the wound is kept small, but some thicken or pull, and minor revision procedures can help later. Cure rates for primary basal cell carcinoma treated with Mohs surgery are high, and rates for recurrent tumours and squamous cell carcinoma are also good, although no treatment removes all risk of recurrence. People who have had one skin cancer are more likely to develop another, so regular skin checks and daily sun protection remain important for life.