History of Mohs Surgery

Early Events in the Development of the Mohs Technique

The Mohs surgical technique was developed in the 1930’s by Dr. Frederic Mohs, a general surgeon at the University of Wisconsin. This important development occurred while he was studying various injectable irritants to evaluate the in vivo inflammatory response in transplantable rat cancers and normal tissue. In the course of this study, Dr. Mohs noted that injected 20% zinc chloride solution inadvertently caused tissue necrosis in tumor and normal tissue. Further, he found that microscopic examination of this necrotic tissue showed well-preserved tumor and cell histology, the same as if the tissue had been excised and immersed in a fixative solution. This discovery formed the basis for a method by which cancers could be excised under complete microscopic control. This fixed tissue technique was utilized for over a decade, with Dr. Mohs being its pioneer, advocate, and lone practitioner. Long-term follow-up of his patients was carefully documented and gave further testimony to the effectiveness of this treatment. In 1953 a revolutionary breakthrough occurred while filming the removal of an eyelid carcinoma for educational purposes. An involved margin in the first level caused a delay in filming, this development necessitating utilization of horizontal frozen sections for the second and third levels. This fresh tissue technique worked so well that Dr. Mohs continued to use it for most eyelid cancers. He also found the technique useful for small and medium sized cancers at other sites, and subsequently continued to use the fresh tissue technique for multiple other skin cancers.

In 1969 Dr. Mohs reported the use of the fresh tissue technique for sixty-six basal cell carcinomas and for squamous cell carcinomas of the eyelid, with five-year cure rates of 100%. A corroborating series of data was instrumental in convincing the medical community of the validity of the fresh tissue technique, which had not yet largely replaced the fixed tissue technique. It is now well-established that the five-year cure rates using fresh tissue technique are equivalent to that of the fixed tissue technique. The fixed tissue technique is still recommended by some Mohs surgeons, however, for selected tumors.

Mohs Surgery’s Evolution as a Dermatologic Procedure

Dermatologists naturally gravitated to the Mohs technique and came to dominate the field, largely due to their training and expertise in skin cancer pathophysiology, cutaneous histopathophysiology, dermatologic surgery, and repair of complex defects. From the 1950’s to the 1970’s, Mohs surgical training was conducted on an informal basis. Training sessions lasted from several days to several months, and took place both in Dr. Mohs’ Chemosurgery Clinic and in the offices of physicians who had learned the technique firsthand from Dr. Mohs.

First Formal Organization of Mohs Surgeons

In 1967 the American College of Chemosurgery was formed, consisting primarily of dermatologists. By the 1970’s, several dermatology residency programs were beginning to provide training in Mohs surgery. In the 1980’s the American College of Chemosurgery began offering formal post-residency fellowships in Mohs surgery, and in 1986 officially changed its name to the American College of Mohs Micrographic Surgery and Cutaneous Oncology to reflect the predominance of the fresh tissue technique.