Mohs Surgery for Skin Cancer

What is the history of Mohs Surgery?

Frederic Mohs – Mohs Surgery

Frederic Edward Mohs, a general surgeon, developed the Mohs Micrographic Surgery technique in the 1930’s to remove skin cancer. He was a medical student at the University of Wisconsin-Madison. The advantages of the Mohs procedure is it has a very high cure rate for treating skin cancers while maximally preserving surrounding healthy tissue.

Dr. Mohs began developing his treatment experimenting on rats, puppies, and other animals.  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. This mixer became to be known as “Mohs Paste”. The process would take days to complete. He treated his first human patient on June 23, 1936.
Mohs first tried to publish his findings and encouraged surgeons to learn the procedure. Initially, this was largely unsuccessful, as many surgeons were not comfortable learning skin pathology and laboratory techniques. Today, most Mohs procedures are performed by dermatologists, plastic surgeons, otolaryngologists, and pathologists.
Mohs’ technique was later modified by Perry Robins in the 1970s, using fresh-tissue frozen histology. Rather than using the anesthetic Mohs paste, a local anesthetic is used. The fresh skin specimen is then mounted on a cryostat, and frozen sections are examined. This allowed the tissue to be examined the same day and the complete procedure to be completed in one day. This method is now commonly referred to as Mohs surgery, and occasionally chemosurgery, in reference to the Mohs paste that Mohs initially used.

Who are good candidates for Mohs Surgery?

Mohs surgery is indicated for basal and squamous cell carcinomas (BCCs and SCCs) with the following characteristics:

  • Cancers on the nose, eyelids, lips, ears, hands, feet and genitals.
  • Cancers that have recurred after initial treatment.
  • Cancers that were not completely removed by other treatment techniques.
  • Cancers with difficult-to-see borders.
  • Cancers with morphic growth patterns.

It is also used for:

  • Dermatofibrosarcoma
  • Extramammary Paget’s disease
  • Merkel Cell Carcinomas
  • Sebacious carcinomas
  • Microcystic adnexal carcinomas

BCCs and SCCs on the abdomen, chest, back, arms and legs, standard treatments such as surgical excision, cryosurgery (freezing), curettage and electrodesiccation (scrapping and burning) and topical medications may provide adequate therapy.

What are the cure rates for Mohs Surgery?

The clinical 5 year cure rates with Mohs surgery:
1. Review of 4085 cases of primary and recurrent cancer of face, scalp, and neck: Cure rate of 96.6%.
2. Review of 1065 cases of squamous cell carcinoma of face, scalp, and neck: Cure rate 94.8%.
3. Review of 2075 cases of basal cell cancer of the nose both primary and recurrent, cure rate 99.1%.
4. Cure rate for basal cell cancer of the ear, less than 1 cm, 124 cases, cure rate 100%.
5. Cure rate of basal cell cancer of the ear, 1 to 2 cm, 170 cases, 100%.

How is Mohs Surgery performed?Mohs Surgery Skin Cancer Procedure

The Mohs process examines 100 percent of the tissue margins under the microscope, whereas in standard surgical excision only 1 percent of the margins are examined microscopically. Mohs surgery also conserves the greatest amount of healthy tissue, giving you the smallest scar possible. The procedure is cost-effective because the cancer removal, microscopic evaluation and, in most cases, wound reconstruction are all done in one visit, and the cure rate is over 98 percent.

The Mohs procedure is a pathology sectioning method that allows for the complete examination of the surgical margin. It is different from the standard bread loafing technique of sectioning, where random samples of the surgical margin are examined.

Mohs surgery is performed in four steps:

  1. Surgical removal of tissue (Surgical Oncology)
  2. Mapping the piece of tissue, freezing and cutting the tissue between 5 and 10 micrometers using a cryostat, and staining with hematoxylin and eosin (H&E) or other stains including Toluidine Blue.
  3. Interpretation of microscope slides (Pathology)
  4. Closure of the surgical defect with possibility of reconstruction of the surgical defect (Reconstructive Surgery)

Details of the Procedure

The procedure is usually performed in a physician’s office under local anesthetic. It may also be performed at an outpatient surgery center if a large reconstruction is required after the Mohs surgery is complete or if the surgeon uses a dermatopatholgist to review the slides. A small scalpel is utilized to cut around the visible tumor. A very small 1-2 mm surgical margin of “free margin” or uninvolved skin is cut with the specimen. In a classic standard excision, a 4-6 mm margin is taken with the specimen. The specimen is then marked with suture to orient the tissue usually at the 12 o’clock position.

Mohs Surgery Skin Cancer Microscope Pathology

The fresh specimen is then processed. It is cut on the cryostat and placed on slides and stained with H&E. The slides are then read by a Mohs surgeon or pathologist for cancerous cells. If cancer cells are found, their 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. Once completed, the defect is closed directly or with a local/regional flap or skin graft.

The method for mapping the edges of the specimen utilizing frozen section histology is called : Complete Circumferential Peripheral and Deep Margin Assessment (CCPDMA). It is this specific technique that allows the smallest amount of normal tissue to be removed with the highest cure rate.

Mohs Surgery Basal Cell Skin Cancer

Basal Cell Skin Cancer

Imagine an orange cut in half as the CCPDMA layer. The peel is the surgical margin. One can remove this peel and flatten it out on a glass slide to examine the edges for invasive cancer. The mapping is simply how one stains and labels the sections for a microscopic examination. The sections can be processed in one piece (using relaxing incisions at multiple points, or hemisectioned like a “Pac-Man” figure), or cut in halves, cut in quarters, or cut in multiple pieces. Single piece processing is used for small cancers, and multiple piece processing is used for large cancers. Single piece sectioning prevents errors introduced by soft, hard-to-handle tissue; or from accidental dropping or mislabeling of specimen. Multiple sectioning prevents compression artifacts, separation of tissue, and other logistical problems with handling large thin sheets of frozen skin.
Mohs Surgery Skin Cancer Pathology
Mohs surgery is performed using fresh tissue while frozen section histology may or may not be CCPDMA. Non-CCPDMA histology usually utilizes a random tissue sampling technique called “bread loafing”. Bread loafing is a statistical sampling method which examines less than 5% of the total surgical margin. Imagine pulling 5 slices of bread out of a whole loaf of sliced bread and examining only those 5 slices to visualize the whole loaf. In CCPDMA processing, the entire surgical margin is examined. Imagine one who examined the entire outside crust of the same loaf of bread. In statistical terms, the more slices of bread one examines, the lower the “false negative” rate will become. False negatives occur when a pathologist reads cancer excision as “free of residual carcinoma”, even though cancer might still be present in the wound and missed because of the random sampling. The alternatives to Mohs surgery are CCPDMA based surgical excision and non-CCPDMA surgical excision. Mohs and CCPDMA pathologists have perfected methods of examining the entire surgical margin.

Dr. DeConti has been performing Mohs Surgery for skin cancer with reconstruction since 1992. He underwent extensive training at the University of Virginia performing Mohs Surgery, repairs and reconstruction in the Department of Dermatology and the Department of Plastic Surgery. He has performed over 15,000 skin cancer excisions.

To learn more about how Mohs Surgery can benefit you, call 804 673-8000 and schedule a Mohs Surgery skin cancer consultation at DeConti Plastic Surgery today.  Dr. DeConti is a participating provider with all the major insurance companies including Medicare.

CareCredit Richmond Virginia DeConti Plastic Surgery
Top