Mohs micrographic surgery, which is performed in the office using local anesthesia, is a state-of-the-art treatment for skin cancer in which the physician serves as a surgeon, pathologist, and reconstructive surgeon. It yields the highest cure rate of all skin cancer treatments, with cure rates approaching 99% for tumors that have not previously been treated. The procedure relies on the precision and accuracy of examining tissue under a microscope to trace and ensure removal of the skin cancer, which may have roots that extend beyond what is visible to the naked eye. In addition, the removal of healthy skin is minimized, resulting in the smallest possible surgical defect and thereby decreasing the potential for scarring.
Mohs micrographic surgery was developed by Frederic E. Mohs, M.D. in 1936 at the University of Wisconsin. In its original form, described as “chemosurgery”, the technique utilized a 20% zinc chloride fixative paste that was applied directly to the skin of the patient for fixation of the tissue. Subsequently, the involved skin was surgically removed by serial excision with microscopic control of the tissue margins.
Removal of tissue was performed in layers and color coded with dyes in order to orient specimens to the patient. Dr. Mohs created a unique technique of color-coding excised specimens and developed a mapping process to accurately identify the location of remaining cancerous cells. This original “chemosurgery” technique, which is no longer performed, was very painful and sometimes took days to complete.
The surgical procedure has been extensively refined over the last seven decades, but it still relies on the fundamental principles of color-coded mapping of excised specimens and their thorough microscopic examination. Surgeons now excise the tumor in layers and examine the fresh tissue immediately. This reduces the normal treatment time to one visit and allows for immediate reconstruction of the wound.
In 1967, the American College of Mohs Micrographic Surgery and Cutaneous Oncology was formed to recognize surgeons who have completed specific, certified training in the Mohs technique. The College also functions as a regulatory and certification body for over 60 Mohs fellowship training programs and provides a source of continuing education for more than 700 practitioners of Mohs Micrographic Surgery.
Mohs Micrographic Surgery is primarily used to treat basal and squamous cell carcinomas. Mohs Surgery is indicated when:
Mohs Micrographic Surgery provides the highest possible cure rate of all skin cancer treatments. The cure rate for basal cell carcinomas that have not been previously treated exceeds 99% and the cure rate for previously untreated squamous cell carcinomas is 97%. The cure rates for recurrent basal cell carcinomas and squamous cell carcinomas are 97% and 90%, respectively.
The high cure rate provided by Mohs surgery is due to the unique and highly specialized tissue processing which occurs after the skin cancer has been removed from the patient. With Mohs surgery, horizontal sections are cut from the specimen. This is analogous to using a cheese slicer to remove a thin layer from the edges and base of the specimen with a single cut. This allows 100% of the peripheral and deep margins to be assessed so that any areas where skin cancer cells extend beyond the wound edges will be detected.
In contrast, other non-Mohs types of tissue processing used in skin cancer treatment involve vertical sectioning, in which the specimen is cut like a loaf of bread and the edges of the slices “sampled.” With this technique, less than 1% of the true surgical margins are assessed, which may result in a failure to detect areas of cancer that have extended past the surgical margins.
Thus, it is the way in which the tissue is processed that makes the Mohs procedure unique and provides the highest possible cure rate in treating skin cancer.