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Mohs Surgery

The Mohs Process
The Mohs Process - Original tumor is presented. Tissue is removed. *Photos provided courtesy of Skin Cancer Foundation.
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The Mohs Process
The Mohs Process - Tissue is inked for orientation and map of tissue is drawn. Tissue is sectioned and placed on a glass slide. The glass slide is stained. *Photos provided courtesy of Skin Cancer Foundation.
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The Mohs Process
The Mohs Process - Surgeon examines slide and identifies residual cancer. Surgeon marks the map corresponding to the location of the cancer. Surgeon returns to bedside with map to precisely excise remaining cancer. *Photos provided courtesy of Skin Cancer Foundation.
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The Mohs Process
The Mohs Process - Process is repeated until no cancer remains; wound is closed. Healing shown two years after surgery.
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The Mohs Process
Mohs Surgery is the single most effect technique for removing Squamous Cell and Basal Cell Carcinomas, shown here. These are the two most popular types of skin cancer.
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The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process
The Mohs Process


Mohs Surgery

Originally developed in the 1930s, Mohs micrographic surgery has been refined into the most advanced, precise, and effective treatment for an increasing variety of skin cancer types. With the Mohs technique, physicians can precisely identify and remove an entire tumor while leaving the surrounding healthy tissue intact and unharmed. It is accepted as the single most effective technique for removing Basal Cell Carcinoma and Squamous Cell Carcinoma (BCCs and SCCs), the two most common skin cancers.

The Mohs procedure involves surgically removing skin cancer layer by layer and examining the tissue under a microscope until healthy, cancer-free tissue around the tumor is reached. Mohs surgery has the highest success rate of all treatments for skin cancer – up to 99%.

Advantages of Mohs Surgery

Mohs surgery is unique and so effective because of the way the removed tissue is microscopically examined, evaluating 100% of the surgical margins. The pathology is reviewed on site by the Mohs surgeon, who is specially trained in the reading of these slides, who can then remove more tissue if the margins are not clear. Advantages of Mohs surgery include:

  • Ensuring complete cancer removal during surgery, virtually eliminating the chance of the cancer growing back.
  • Minimizing the amount of healthy tissue lost.
  • Maximizing the functional and cosmetic outcome resulting from surgery.
  • Repairing the site of the cancer the same day the cancer is removed, in most cases.
  • Curing skin cancer when other methods have failed.
  • Other skin cancer treatment methods blindly estimate the amount of tissue to treat, which can result in the unnecessary removal of healthy skin tissue and tumor re-growth if any cancer is missed.

Which cancers need Mohs Surgery?

Mohs surgery offers the highest cure rate among treatments for skin cancer and can be used for practically any type of skin cancer. There are many other acceptable skin cancer treatment options including freezing (cryosurgery), scraping & burning, surgical removal (excision), and laser surgery, which all require the surgeon to estimate how extensively to treat the area around the tumor. There are many advantages to Mohs surgery compared to other other skin cancer treatments including its high cure rate and cost-effectiveness. It is especially appropriate for skin cancers that:

  • Develop on areas where preserving cosmetic appearance and function are important.
  • Have recurred after previous treatment or are likely to recur.
  • Are located in scar tissue.
  • Are large.
  • Have edges that are ill-defined.
  • Grow rapidly.

The Mohs Procedure

The Mohs surgery procedure seems simple: the surgeon removes the cancer, carefully checks to be sure the he or she got it all, then repairs the wound. American College of Mohs Surgery members, however, train in and practice the complex nuances of this process for years so they are prepared to handle any situation they may encounter. The steps followed for the Mohs surgical procedure are:

  • Step One: The roots of a skin cancer may extend beyond the visible portion of the tumor. If these roots are not removed, the cancer will recur. A surgery starts with surgeon examining the visible lesion and planning what tissue to remove. The patient then receives local anesthesia, and the Mohs surgery begins.

  • Step Two: The surgeon removes the visible portion of the tumor using careful surgical techniques.

  • Step Three: The surgeon next removes a deeper layer of skin and divides it into sections. With the help of technicians, the surgeon then color-codes each of these sections with dyes and makes reference marks on the skin to show the source of the sections. A map of the surgical site is then drawn to track exactly where each small portion of tissue originated.

  • Step Four: In a laboratory, the surgeon uses a microscope to examine the undersurface and edges of each section of tissue in search of evidence of remaining cancer.

  • Step Five: If the surgeon finds cancer cells under the microscope, he or she marks their location on the "map" and returns to the patient to remove another deeper layer of skin — but only from precisely where the cancer cells originated. This method ensures that the Mohs surgery results in the smallest scar possible.

  • Step Six: The removal process stops when there is no longer any evidence of cancer in the surgical site. Because Mohs surgey removes only tissue containing cancer, it ensures that the maximum amount of healthy tissue is kept intact. At this point, the surgeon discusses reconstruction options, should they be required, and then post-operative care. Mohs surgery recovery tends to be easily manageable because of the use of local anesthesia and the careful surgical techniques.

Mohs Surgery Post-Operative Care

After a Mohs surgery procedure, most patients find the recovery process simple and easy thanks to the streamlined surgical approach that leaves surrounding tissue unharmed. You may or may not undergo a repair process to mend the wound left by the surgery. A number of different reconstruction options exist, and instructions for aftercare are different depending on which approach the surgeon takes. The surgeon and his or her medical team will provide you with detailed instructions to follow at home. These instructions will include:

  • Information about when to change bandages and how to clean the surgical site
  • Medication information about prescription or over-the-counter pills or topical ointments
  • A timeline for when you can return to certain activities, such as wearing makeup or exercising
  • A schedule of follow-up appointments to remove any stitches and monitor your healing
  • Recommendations for treating your Mohs surgery scar to ensure it heals and fades quickly

Although Mohs micrographic surgery has an extremely high success rate that frequently prevents skin cancer from recurring at the same site, it is very important to monitor your skin since you are already prone to skin cancer. Your dermatologist may arrange a series of follow up appointments that may extend many years into the future.


American College of Mohs Surgery
American Society for Mohs Surgery
Skin Cancer Foundation


Why is it called Mohs surgery? Is Mohs an acronym?

The term "Mohs" refers to Dr. Frederic Mohs, Professor of Surgery at the University of Wisconsin, who developed this surgical technique in the 1930s. The technique has undergone many refinements and has come to be known as "Mohs micrographic surgery" or simply "Mohs surgery" in honor of Dr. Mohs.

What is Mohs surgery?

Dr. Mohs recognized that a skin cancer often resembles the "tip of the iceberg" with more tumor cells growing downward and outward into the skin like the roots of a tree. These "roots" are not visible with the naked eye, but can be seen under a microscope.

Mohs surgery is a highly specialized and precise treatment for skin cancer in which the cancer is removed in stages, one tissue layer at a time. It is an outpatient procedure, performed under local anesthesia, and is distinguished by a specific technique of tissue examination that is unique to Mohs surgery. Although other surgical specialists may check excision margins, this form of pathologic examination of the tissue is not the same as Mohs surgery.

Once a tissue layer is removed, its edges are marked with colored dyes, and a map of the specimen is created. The tissue is then processed onto microscope slides by a Mohs histotechnician. These slides are carefully examined under the microscope by the Mohs surgeon so that any microscopic roots of the cancer can be precisely identified and mapped. If cancer cells are seen, an additional tissue layer is removed only in areas where the cancer is still present, leaving normal skin intact. This saves as much normal, healthy skin as possible.

Once the cancer has been removed, the Mohs surgeon will explain options for repair of the wound, including natural healing (granulation), stitching the wound together using a side-to-side closure, or using a skin flap or graft.

It's important to choose a fellowship trained Mohs surgeon who is a member of the American College of Mohs Surgery. Mohs College surgeons have undergone at least 1 year of fellowship training beyond dermatology residency, which allows for additional experience in all of these specialized processes and techniques.

I don't see anything after my biopsy. Do I really need to be treated?

Yes. Following a biopsy, your skin cancer may no longer be visible. However, the surface lesion that was removed can represent the "tip of the iceberg." More tumor cells may remain in the skin. These can continue to grow downward and outward, like roots of a tree. These "roots" are not visible with the naked eye. If they are not removed, the tumor will likely reappear and require more extensive surgery.

Tumors that are neglected can spread deeply into the skin and invade nearby structures. On rare occasions, these cancerous cells can metastasize to lymph nodes and other organs in the body.

Why does my skin cancer need to have Mohs surgery?

Mohs surgery has the highest cure rate. It is appropriate for most skin cancers and especially suitable for skin cancer that:

  • Is in an area where it is important to preserve healthy tissue for maximum functional and cosmetic result.
  • Was treated previously and has come back.
  • Is located near scar tissue.
  • Is large.
  • Does not have clearly defined edges.
  • Is growing rapidly or uncontrollably.
  • Is of an aggressive subtype (i.e., sclerosing or infiltrating basal cell carcinoma).
  • Develops in organ transplant or lymphoma patients.

Please note: the above list is not exhaustive of all of the instances where Mohs surgery is the most appropriate option for your skin cancer.

How long does Mohs surgery take?

Although Mohs surgery can take longer than other techniques to perform, advances in technology, such as automated staining of tissue samples, have made it quicker. While it is impossible to predict exactly what timeframe to expect for each Mohs surgery procedure, the entire procedure usually lasts several hours. Rarely, clearing the tumor and reconstructing the defect can take the better part of a day. A consultation with the Mohs surgeon prior to your procedure will allow for the surgeon to understand the unique qualities of your situation and enable him/her to more clearly estimate the extent of the timeframe for the surgery.

Will Mohs surgery leave a scar?

Yes. As will any treatment for skin cancer, Mohs surgery will leave a scar.

Mohs surgery preserves as much healthy skin as possible and maximizes options for repairing the surgical defect, once the tumor is completely removed. Once the Mohs surgeon has completely removed your skin cancer through Mohs surgery, reconstruction for optimizing the final functional and cosmetic result becomes the highest priority. Generally, a post-surgical scar improves with time and can take up to 1 year or more to fully mature. As your surgical site heals, new blood vessels can appear and support the healing changes occurring underneath the skin. This can result in the reddish appearance of the scar. This change is temporary and will improve with time.

In addition, the normal healing process involves a period of skin contraction, which often peaks 4 to 6 weeks after the surgery. This may appear as a bumpiness or hardening of the scar. On the face, this change is nearly always temporary and the scar will soften and improve with time. If you have a history of abnormal scarring, such as hypertrophic scars or keloids, or if there are problems with the healing of your scar, injections or other treatments may be used to optimize the cosmetic result. Your Mohs surgeon is available for you throughout the healing process to discuss any concerns that may arise.

Is Mohs surgery the most cost-effective treatment option?

When assessing the cost-effectiveness of Mohs surgery there are several factors to consider. Because of the number of personnel involved as well as the advanced technology required, the initial procedure is often more costly than other treatment methods. However, because of the procedure's high success rate, most patients require only a single surgery. This surgery usually includes the repair of the wound as well. While other methods might initially be less expensive than Mohs surgery, additional surgeries and pathology readings are required to repair the wound and to treat the cancer if it is not completely removed. Each of these additional surgeries and pathology readings will require separate fees, while a single Mohs surgery procedure includes all of these into one fee.


American College of Mohs Surgery


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