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Mohs surgery

Mohs Surgery, created by a general surgeon, Dr. Fredrick E. Mohs, is microscopically controlled surgery that is highly effective for common types of skin cancer, with a cure rate cited between 97 to 99% for basal cell carcinoma, the most common type of skin cancer, and for squamous cell carcinoma. It has been used in the removal of melanoma-in-situ, but only by a few physicians. Because the Mohs procedure is micrographically controlled, it provides precise removal of the cancerous tissue, while healthy tissue is spared. For this reason, Mohs surgery results in a significantly smaller surgical defect and an improved cosmetic result compared to other surgical methods of skin cancer treatment. In certain area, especially the nasal tip, nasal ala, and the eyelids, radiation therapy can preserve viable tissue and result in better cosmetic appearance than Mohs surgery (See figure I, demonstrating the bilobed transposition flap with resulting visible scarring)

The Mohs procedure is recommended for skin cancer removal in anatomic areas where maximum preservation of healthy tissue is desired for cosmetic and functional purposes (the face, eyelids, nose, ear, fingers, genital area), for cancers with indistinct margins, and for recurrent cancers in scar tissue. It is especially indicated for lesions that have recurred following prior treatment, or for lesions in anatomic areas that have the greatest likelihood of recurrence (eg., the side of the nose). Mohs surgery is relatively expensive when compared to other surgical modalities alone, but has been shown to be less expensive compared with other modalities for aggressive tumors or tumors in high risk locations due to the inherent high risk of recurrence in these tumors and potential future associated costs. For this reason, it is used generally for recurrent tumors, indistinct tumors, or tumors in areas such as the face, where sparing normal tissue around the skin cancer is paramount.

Originally, Dr. Mohs used an escharotic agents made of zinc chloride and bloodroot (contains the alkaloid sanguinarine that is derived from the root of the plant Sanguinaria canadensis). This paste is very similar to "Hoxsey's paste". Harry Hoxsey, a lay cancer specialist was developing a herbal tonic and paste designed to treat internal and external cancers. Hoxsey recommended applying paste to the affected area and within days to weeks, the area would necrose (cell death), separate from surrounding tissue and fall out. Dr. Mohs applied a very similar paste after experimenting with a number of compounds to the wound of his skin cancer patients. They were to leave the paste on the wound overnight, and the following day, the skin cancer and surrounding skin would be anesthetic, and ready to be removed. The specimen was then excised, and the tissue examined under the microscope. If cancer remains, more paste was then applied, and the patient would return the following day. Later, frozen section histopathology and local anesthetic allowed the procedure to be performed the same day, with less tissue destruction, and similar cure rate. The term "chemosurgery" remains today, and is used synonymously with Mohs micrographic surgery.

Additional recommended knowledge


Mohs procedure

Mohs surgery is performed by a Mohs skin cancer surgeon in four steps:

  • Surgical removal of tissue (Surgical Oncology)
  • Mapping the piece of tissue, freezing and cutting the tissue between 5 and 10 micrometres using a cryostat, and staining with H&E or other stains (including T. Blue)
  • Interpretation of microscope slides (Pathology)
  • Reconstruction of the surgical defect (Reconstructive Surgery)

After each surgical removal of tissue, the specimen is processed (look here for a clay animation of tissue processing), cut on the cryostat and placed on a slides, stained with H&E and then read by the Mohs surgeon who examines the sections for cancerous cells. If cancer is found, its location is marked on the map (drawing of the tissue) and the surgeon removes the indicated cancerous tissue from the patient. This procedure is repeated until no further cancer is found.

The mapping combined with the unique "smashing the pie pan" method of processing is the essential of Mohs surgery. If one imagine an aluminum pie pan as the blood covered surgical margin, and the top of the pie is the crust covered surface of the skin - the surgeons goal is to flatten the aluminum pie pan into one flat sheet, mark it, stain it, and examine it under the microscope. The mapping is simply how one stain and label the sections for microscoping exam. The sections can be processed in 1 piece (using relaxing incisions at multiple points, or hemisectioned like a "pacman" figure), cut in halves, cut in quarters, or cut in multiple pieces. Single piece processing is acceptable for small cancers, and multiple piece sectioning facilitate processing and prevent artifacts. Single piece sectioning prevent errors introduced by soft hard to handle tissue, or from accidental dropping or mislabeling of specimen. Multiple sectioning prevent compression artifact, separation of tissue, and other logistical problems with handling large thin sheet of frozen skin.

Some physicians believe that frozen section histology is the same as Mohs micrographic surgery, and it is not. Standard histology processing is a random tissue sampling technique, examining less than 10% of the total surgical margin (imagine pulling 5 slices of bread out of a whole loaf of sliced bread and examining only 5 slices to visualize the whole loaf). In Mohs processing, the entire surgical margin is examined (imagine one who examined the entire outside crust of the same loaf of bread). In statistic term, the more slices of bread one examine, the lower the "false negative" rate will be come. False negative occurs when a pathologist read cancer excision as "free of residual carcinoma", eventhough cancer might be present in the wound and missed because of the random sampling. In reality, most pathology lab examine only 3 to 8 sections of this "loaf" in their margin determination. While a diligent pathologist can cut and process a standard excision to get the same margin control as Mohs surgery, it is seldom done, as tissue processing is very difficult in practice. The alternative to Mohs surgery is when a pathologist request the processing to be done by "cutting through the block". Again, this method approaches that of Mohs surgery, but still is not as good. Cutting through the block will result in the random discarding of many slices, but does greatly decrease the incidence of "false negative" reports. Dr. Mohs perfected a simple and efficient way to "flatten" and examine the entire surgical margin.

Mohs Surgery Case Studies

Photos courtesy of Dr. B. Cowan

CASE STUDY 1: Left Nasal Rim Skin Cancer

Mohs surgery case study 1.png
Click to view complete slide-show and the surgeon's comments for the Left Nasal Rim Skin Cancer case study

CASE STUDY 2: Right Lower Lip Skin Cancer

Mohs surgery case study 2.png
Click to view complete slide-show and the surgeon's comments for the Right Lower Lip Skin Cancer case study

CASE STUDY 3: Left Temple Basal Cell Cancer

Mohs surgery case study 3.png
Click to view complete slide-show and the surgeon's comments for the Left Temple Basal Cell Cancer case study

About Mohs surgeons

The Mohs surgeon must understand the biologic behavior of several types of skin tumors in order to provide comprehensive management of cutaneous oncology. The Mohs surgeon must have extensive training in the surgical removal of skin cancer, the microscopic analysis (pathology) of the tumor, and reconstructive surgery of the skin and underlying structures. In addition, Medicare requires that the same physician serve as surgeon and pathologist. All Mohs surgeons must have a CLIA certified laboratory.

The American College of Mohs Surgery was established in 1967 and named after Frederic Mohs, who first developed the technique in the 1940s. This organization's members are board certified dermatologists who have become proficient and experienced in the use of Mohs Micrographic Surgery. In order to become a member of this college, member physicians must be board certified in a field of medicine or surgery (usually dermatology) and then complete an additional 1 to 2 years of post-residency fellowship training, with exposure to complex tumors and reconstructive plastic surgery of the skin. These College sponsored fellowships are not recognized by the The Accreditation Council for Graduate Medical Education. The College has grown to 850 members. Because of the importance of properly prepared frozen slides to the Mohs surgical procedure, the College founded the American Society for Mohs Histotechnology in 1995. The purpose of the ASMH is to provide training and support for laboratory personnel working for Mohs College members.

The American Society for Mohs Surgery is a non-profit professional medical society of over 800 dermatologists, pathologists, and Mohs technicians. Founded in 1990, the ASMS is dedicated to the highest quality patient care and education relative to Mohs surgery as a specialized surgical treatment for skin cancer. This organization's Fellows are board certified dermatologists who have become proficient and experienced in the use of Mohs micrographic surgery. Some ASMS Fellows have completed an ACMMSCO sponsored Mohs fellowship, but most received their Mohs training during Dermatology Residency and post-residency training and experience. ASMS requires yearly peer case review of its Fellow members.

The Board of Medical Subspecialities considers Mohs micrographic surgery as part of the field of dermatology and does not recognize it as a separate subspeciality.

The American Academy of Dermatology is the largest organization of board certified dermatologists, many of whom perform dermatologic and Mohs micrographic surgery. With a membership of over 15,000, it represents virtually all practicing dermatologists in the United States and Canada and has specific member information regarding those performing Mohs micrographic surgery.

The American Society for Dermatologic Surgery founded in 1970 is the largest organization of board certified dermasurgeons with over 5000 members who perform dermatologic surgeries including Mohs micrographic surgery. The mission of the Society is to promote excellence in the subspecialty of dermatologic surgery and foster the highest standards of patient care.

The official medical journal for Mohs surgery, Dermatologic Surgery, is published by the American Society for Dermatologic Surgery and is the official journal of The American College of Mohs Surgery and the official publication for the American Society for Dermatologic Surgery.

The The Accreditation Council for Graduate Medical Education is responsible for the accreditation of post-MD medical training programs within the United States. Accreditation is accomplished through a peer review process and is based upon established standards and guidelines. Starting in 2005, and ACGME recognized and accredited Procedural Dermatology fellowships have started in the U.S. to train fellows. There is no additional ABMS board certification of dermatologists who have completed a Procedural Dermatology fellowship.

The Association of Academic Dermatologic Surgoens has board certified dermasurgeon professors who have faculty appointments at major teaching hospitals and universities and are engaged in training medical students and residents in the practice of dermatologic surgery and Mohs micrographic surgery.

Patients who desire Mohs surgery for removal of skin cancer should contact a Mohs surgeon for evaluation and treatment of the biopsied lesion.

Future Applications of Mohs surgery

Mohs surgery can be applied to any relatively non-aggressive locally invasive tumors with contiguous growth pattern (i.e. no skipped growth, or metastasis). This explains why it is so effective against the relatively "benign" basal cell carcinoma. Applications to tumors of the head and neck has been reported in the literature, and the medical community should encourage surgical specialties to learn the method and apply it to other locally invasive tumors as well. The American Society for Mohs Surgery encourages non-dermatologist physicians to learn about the procedure, and perhaps, someday, it can be applied to certain neural, osseous, and other solid tumors as well. Today, most Mohs procedures are performed by dermatologists. However, pathologists, plastic surgeons, and otolaryngologists have been trained and are ulitizing Mohs surgery in their practice as well. The practice of the procedure required refined dexterity both as a surgeon and as the lab technician, followed by meticulous histology examination. Many physicians learned the procedure by spending a week or a month with Dr. Frederick Mohs, and many dermatologists today are open to physicians of other specialties to learn and apply the technique to their own unique specialty in the same spirit of the general surgeon, Dr. Frederick Mohs.


  • Bowen G, White G, Gerwels J (2005). "Mohs micrographic surgery.". Am Fam Physician 72 (5): 845-8. PMID 16156344.Full text

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Mohs_surgery". A list of authors is available in Wikipedia.
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