Mohs micrographic surgery is the most effective and advanced treatment for skin cancer today. It offers the highest potential for cure – even if the skin cancer has been previously treated by another method. It differs from other surgical excision techniques which normally involve examination of vertical sections.
The technique was first developed by Dr Frederic E Mohs in the 1930s and has been refined and perfected over the last 50 years, although the unique process of examining horizontal tissue sections, colour coding excised specimens and creating a map to identify location of remaining cancer cells to be excised remains the cornerstone of the procedure. The cure rate for MMS is very high (up to 99%) compared with other treatments for skin cancer, thus MMS has become the treatment of choice for basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) with high risk for recurrence.
Mohs Micrographic Surgery is named after its founder and originator, Frederic E. Mohs, MD. Mohs was born in Burlington, Wisconsin. His father died when he was 3 months old, and the family moved to Madison, where his mother ran a boarding house. After initially considering a career as a radio engineer, he switched to medical studies in college. Mohs began developing his treatment in the 1930s, experimenting on rats, puppies, and other animals. As a medical student from 1929 to 1934, Dr. Mohs conducted cancer research projects while working for his mentor and zoology professor, Michael Guyer. Dr. Guyer was familiar with the preparation of frozen tissue for producing microscopic slides and had authored a book explaining how to harvest and process tissue for microscopic examination. The book focused on the need for examining, drawing and documenting discoveries that were made with the microscope. These microscopic techniques were later used by Dr. Mohs to map out cancer around nerves, blood vessels, muscle and bone. The cancers he examined were removed by shave or saucerizing excision, a technique that removed cancer as a thin disc of tissue so that the tumor and the inflammatory white-cell infiltrate surrounding the cancer could be examined with the microscope.
The breakthrough came when he discovered that applying a combination zinc chloride and bloodroot paste to malignant rat skin tissue allowed it to be removed surgically and examined under a microscope. He treated his first human patient on June 23, 1936. Mohs, who spent his working life at the University of Wisconsin, was a tireless advocate for the surgical procedure he had devised and taught it to doctors from all over the world. After finishing medical school Dr. Mohs began his practice in a one-room clinic of the dermatology suite of the Wisconsin General Hospital in Madison, Wisconsin. The very first Mohs lab consisted of a student desk with a freezing microtome and a staining setup. Sections were processed in the same room where the surgeries were performed. Surgical pathologists and their residents processed the slides for Dr. Mohs, and if a nurse was needed, Dr. Mohs would borrow one from the emergency room. On June 30, 1936, Dr. Mohs treated his first patient, an individual with a squamous cell cancer of the lower lip.
After spending four years studying refining and perfecting his procedure, Dr. Mohs expanded his practice in 1940. Since his procedure involved more surgery than dermatology, his clinic was transferred to the department of surgery. Mohs first tried to publish his findings and encouraged surgeons to learn the procedure. This was largely unsuccessful, as many surgeons were not comfortable learning skin pathology and laboratory techniques. Dermatologists, who are well trained in dermatopathology, and who treat skin cancers on a daily basis, quickly embraced the procedure. Today, most Mohs procedures are performed by dermatologists, although a small number of plastic surgeons, otolaryngologists, and pathologists are also practicing and using the procedure as well.
Which tumours are suitable for Mohs micrographic surgery?
Skin cancers may form with undefined edges and lengthy rootlike extensions that can grow deeply or laterally from the clinically visible lesion. The MMS technique allows almost 100% of the tumour margins to be microscopically examined, very much moree than traditional histological methods. Hence MMS is particularly suitable for the treatment of difficult skin cancers because it is able to identify and remove all cancer tissue including that found in finger-like extensions. This allows higher cure rates and less scarring.
MMS is primarily used to treat basal and squamous cell carcinomas, but can be used to treat less common skin cancers including melanoma. It is particularly useful in the following circumstances. (DermNet NZ)
* Recurrent or incompletely excised BCC and SCC
* Primary BCC and SCC where the edges of the cancer cannot be clearly defined
* BCC and SCC in an area where it is important to preserve healthy tissue for maximum functional and cosmetic result, such as eyelids, nose, ears, lips, genitals, hands, feet
* BCC and SCC that is large (> 2cm in diameter) or growing rapidly.
* Cancer arising in scars or in sites of previous radiation therapy
* High risk or aggressive types of SCC (e.g. infiltrative histology, poorly differentiated)
* Facial melanoma in situ, lentigo maligna type
* Extramammary Paget disease, which has a high risk of incomplete excision and subsequate recurrence
* MMS is also recommended where a patient may have multiple, small, less aggressive tumours situated in the same surgical area, and in young patients who may expect to have further skin cancers on the face in future.
However, most BCC and SCC are clearly defined tumours in low risk sites, and can be dealt with by simple excisional surgery or other methods.