Mohs micrographic surgery
Mohs’ micrographic surgery was first developed by Dr Frederic Mohs in the 1930s. It is a specialised surgical method for removing certain types of skin cancer – usually basal cell cancers (BCC) and squamous cell cancers (SCC).
During the Mohs’ micrographic surgery procedure, the ‘roots’ of the skin cancer are located and removed. This is done in stages by removing the tumour together with a thin (1-2mm) layer of surrounding normal tissue. After each stage the tissue is frozen and cut into thin slices that are then stained with a dye. The edges are then examined very carefully under the microscope. If the tumour is found at the edge of the slice, then a further slice of tissue is removed, but only in the area where the tumour remains. Therefore, close to 100% of the cancer is located and removed.
Sometimes, if the tissue cannot be processed by same-day frozen sections, it is necessary to perform these stages several days apart – this may be recommended in other, more unusual, conditions such as lentigo maligna (slow Mohs’).
There are two main advantages of removing the skin layer by Mohs’ surgery. Firstly, the minimum of healthy skin is removed around the skin cancer, which keeps the wound as small as possible (‘tissue sparing’). Secondly, your dermatological surgeon can be almost certain that the skin cancer is fully removed on the day of the procedure. The disadvantages of Mohs’ are that waiting times for Mohs’ are often longer than for standard excision, as it is a longer procedure (often involving several stages in one day) and not all skin cancers are suitable for removal by Mohs’.
Non-Mohs’ minor operations (called standard excision) also surgically remove skin cancers together with an area of healthy unaffected surrounding skin and some subcutaneous tissue below it. However, the area is usually around 4mm (slightly larger than for Mohs’). Once removed, the skin is sent to the laboratory for examination by a pathologist (a doctor who specialises in looking at the tissue cells with a microscope) to confirm whether the operation has been successful or not. It usually takes about 2 weeks for a pathology report to be available. The report will state whether the skin cancer appears to have been fully removed or not. If it has not been completely removed, a further procedure may be necessary. However, with a standard excision the pathologist is only able to look at a small proportion of the cut area (usually, less than 2% of the area). This means that the pathologist’s report is an estimation of the completeness of removal. We know that (depending on the type of skin cancer) standard excision is sufficient to prevent the tumour coming back around 80-95% of the time.
Therefore, standard excision is a good option for many patients. However, for patients who have skin cancers on the face, or have certain types of tumours, your doctor may recommend Mohs’ Surgery.
Mohs’ procedure is performed by dermatologists or dermatological surgeons who are specially trained in Mohs’ micrographic surgery. This training is an additional 1-2 years over that required to become a consultant dermatologist. The British Association of Dermatologists, in conjunction with the British Society for Dermatological Surgery, have published standards on Mohs’ micrographic surgery and a link to these standards can be found below.
In the NHS, dermatologists and Mohs’ surgeons who are undergoing specialized training may be involved in your care, under the supervision of a consultant Mohs’ surgeon. Occasionally, support may be given by other specialists, eg a plastic surgeon to help remove the tumour or reconstruct the wound, an oculoplastic surgeon for the eye area, or a head and neck surgeon to treat the deepest part of the cancer.