Mohs Micrographic Surgery: A Marvel in Dermatology

Paul M. Graham, D.O.

ucm116427According to the American Cancer Society, skin cancer is by far the most common type of cancer worldwide. Non-melanoma skin cancer accounts for approximately 3 million cases in the United States each year with the incidence continuing to climb. Approximately 1 out of every 3 cancers diagnosed worldwide is a skin cancer. Additionally, 1 out of every 5 Americans will develop a skin cancer during their lifetime. The two most common types of non-melanoma skin caner are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Basal cell carcinoma accounts for approximately 80% of all non-melanoma skin cancer diagnoses. Chronic sun exposure is the single most important cause of all forms of skin cancer with damage often occurring during childhood and adolescence years in those who practice poor sun protection habits.

Basal cell carcinoma vs. Squamous cell carcinoma


Basal cell carcinoma is the most common type of skin cancer worldwide, occurring primarily in fair-skinned individuals with a history of sun exposure. Risk factors include numerous blistering sunburns, immunosuppression, family history of BCC, and a history of radiation exposure. Basal cell carcinoma develops from cells contained within the bottom layer of the epidermis called the basal layer. Fortunately, they are often slow-growing with a very low rate of cancer cell spread (metastasis) outside the primary site of occurrence. It is very important to have all BCCs treated to prevent local surrounding skin destruction if left untreated.

Squamous cell carcinoma (SCC) is the second most common form of skin cancer worldwide. The majority of  SCCs develop in individuals with a history of chronic sun exposure. The closer to the equator one lives, the more likely that individual will develop SCC. The immune system also plays an important role in the development of SCC. Those that are immunosuppressed or on immunosuppressive medication have a significantly higher risk of developing SCCs. Certain high-risk types of the human papillomavirus (HPV) may also play a role in SCC development. This type of skin cancer develops from cells that make up the bulk of the epidermis. Squamous cell carcinoma has a slightly higher risk due to its ability to spread into blood vessels and nerves. It is for this reason why they should be properly treated early on.

Numerous treatment options exist for these non-melanoma skin cancers, including the use of topical immune system modifying medications (5-flurouracil, imiquimod, ingenol mebutate), cryotherapy (freezing), electrodessication and curettage (“scraping and burning”), surgical excision, and Mohs micrographic surgery. After being diagnosed with a non-melanoma skin cancer, your physician will determine the best treatment option based on the lesion size, type, location, and aggressiveness of the skin cancer. Some skin cancers have small “roots” that may extend deeper in the skin, beyond what we can see on the biopsy. In these instances, surgical intervention is needed to completely remove the skin cancer.

What is Mohs micrographic surgery?

Dr-Mohs.jpgMohs micrographic surgery provides a highly specialized and effective treatment option in patients with qualifying skin cancers. This procedure has a 97-99% cure rate, which is superior to many cancer treatments in medicine. Mohs micrographic surgery was developed in 1938 by Dr. Frederick Mohs, a surgery professor at the University of Wisconsin. With this specialized procedure, the skin cancer is conservatively removed while simultaneously attempting to preserve normal skin. The removed portion of the skin is then carefully mapped, color-coded, and prepared for examination under the microscope, which all takes place within the same day. The Mohs surgeon will meticulously examine dermatopathologythe tissue specimen and determine if any residual skin cancer is present. If residual tumor is found, the Mohs surgeon will only go back to that specific location to remove another small portion of tissue. One of the most important aspects of Mohs microscopic surgery is the ability to examine approximately 100% of the skin margins under the microscope, ensuring that all of the skin cancer is completely removed prior to closing the surgical wound.

In contrast, a conventional surgical excision requires several days for both tissue processing and microscopic examination by a trained dermatopathologist. During this process, only approximately  1% of the skin margins are examined. This small percentage of examined skin may contribute to a higher rate of recurrence if adequate surgical margins are not taken at the time of the surgery. In the event that more skin cancer cells are found in the examined skin, the surgeon will therefore have to perform a second surgical excision to completely remove the residual tumor.

Mohs Micrographic Surgery

What are the indications for Mohs micrographic surgery?

  • Large skin cancers on the head and neck
  • Skin cancers in areas where preservation of normal skin is vital
    • Face, scalp, neck, nose, ear, eyelids, lips, hands, and genitalia
  • Sites of high tumor recurrence and risk of tumor spread
  • Recurrent skin cancers
  • Aggressive skin cancers

What can I expect during the procedure?

Mohs micrographic surgery involves a series of stages consisting of the surgical excision followed by immediate microscopic examination of the tissue. The Mohs surgeon is focused on removing the least amount of tissue, while still providing adequate surgical
margins to completely remove the skin cancer. Initially, it is not possible to know the final size suturing-techniques-md-pulpof the surgical wound. This is often dependent on the number of stages that are required to completely remove the skin cancer cells. For reference, approximately 50% of all Mohs micrographic surgery cases require at least 2 stages for complete skin cancer clearance. After all the skin cancer cells are removed, the Mohs surgeon will surgically close the wound and the procedure will be complete. Some wounds may be too large for simple closure and will require a skin graft or flap. In this case, the Mohs surgeon will design a closure that will preserve the skin’s function and movement, while reducing the appearance of the scar. Stay tuned for a future article on skin grafts and flaps used in wound closure.

What should I expect after the procedure?

Following Mohs micrographic surgery, it is recommended to minimize strenuous activity to reduce tension on the wound and decrease the risk of bleeding from blood pressure elevation. Pain is usually minimal but Tylenol may be taken for discomfort. Suture removal time can vary depending on the location of the surgical wound, ranging from 5-14 days. Keep in mind that it often takes 12 months for the surgical wound to regain similar strength of the surrounding skin. Surgical site redness may take up to 6 weeks to fade. The appearance of the scar will fade over time, but in cases of elevated (hypertrophic or keloidal) scars, steroid injections may be used to assist in flattening. Various options exist for the treatment of noticeable scars including resurfacing lasers and microneedling if the cosmetic result is unacceptable.

Advantages of Mohs Micrographic Surgery

  • Highest cure rate of all treatment procedures for skin cancer
  • Preservation of normal skin, allowing for a good cosmetic outcome, while reducing the appearance of the surgical scar
  • Low associated risk with local anesthesia (numbing) in an outpatient setting


PhotoCredit:, UCHospitals,,, Healthwise,,,


  1. James, William D, Dirk M. Elston, Timothy G. Berger, and George C. Andrews. Andrews’ Diseases of the Skin: Clinical Dermatology. London: Saunders/ Elsevier, 2011. Print.

Published by Dr. Paul M. Graham

Paul M. Graham, D.O. (Founder/Editor-in-chief) founded Dimensional Dermatology in May 2016 with the vision to provide concise, easy to read, up-to-date dermatology and aesthetic medicine information to patients, medical staff, providers, and the general public. Dr. Graham is currently completing his training as a cosmetic dermatologic surgery fellow in Virginia Beach, Virginia at the McDaniel Laser and Cosmetic Center. He completed his dermatology training at St. Joseph Mercy Hospital and was a clinical instructor at Michigan State University. He received his B.S. degree as Summa Cum Laude at Old Dominion University, his D.O. degree as Cum Laude at Edward Via College of Osteopathic Medicine, completed his internship at Largo Medical Center in Largo, Florida as chief intern, and completed his dermatology residency training at St. Joseph Mercy Hospital Ann Arbor, Michigan.

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