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What is Mohs Micrographic Surgery?

Mohs micrographic surgery is a highly specialized procedure for the complete removal of skin cancer.  It differs from other surgical treatments in that the tissue is meticulously oriented, mapped, and color-code after removal, and the mapped tissue is processed so that the Mohs surgeon can examine 100% of the margin.  In this way, the surgeon can remove every cancer cell.  Standard pathologic techniques used in the vast majority of non-Mohs surgical excisions examine only a portion of the margin, providing only an estimate of whether the margins are clear. As a result, the cure rates are much lower than in Mohs surgical excisions.


What are the advantages of Mohs surgery?

The Mohs surgeon has two goals:
(1) Remove every last cancer cell for complete cure
(2) Spare healthy tissue to keep the resulting wound as small as possible

Fortunately, Mohs surgery can achieve both goals.  The detailed analysis of tissue margins leads to the highest chance of cure, allows smaller surgical margins to be taken.  For treatment of most skin cancers, only 1 to 1.5 millimeter margins are taken in Mohs excisions, compared to 4 to 5 millimeter “safety margins” that are recommended with standard excision.

There is an added benefit of Mohs surgery. Because the margins are tested with frozen section pathology, the doctor and patient know that the tumor has been cleared
on the day of surgery. This prevents a call back a few days later to perform additional surgery once more tumor had been identified, as is common with standard excision techniques.


What are the disadvantages of Mohs surgery?

The main trade-off with Mohs surgery is the time taken to complete the procedure.  The patient trades a lengthier procedure for higher cure rate, convenience of knowing the surgery is complete the day of the procedure, and a potentially smaller wound, resulting in an easier wound repair and smaller scar.


When is Mohs surgery beneficial?

Mohs surgery is essential in certain situations.  First, many cancers are more aggressive and have more spread wider and deeper than can be seen with the unaided eye.  In these situations, the cancer can develop “roots” similar to those of a plant that cannot be seen unless the entire margin is analyzed with the microscope.  This may be very important in certain patients with low immune systems due to disease or medication that can allow tumors to grow rapidly and beyond what can be seen with the eye. 

Also, as Mohs surgery is a tissue-sparing technique, With its more narrow margins, patients with cancers of cosmetically sensitive areas such as the eyelids, nose, lips, ears can be cured without causing more tissue loss than is necessary.  This leads to easier repair and reconstruction of the wounds, and ultimately, better long-term cosmetic outcomes.  Also, Mohs really shines when it comes to curing recurrent cancers that in many cases cannot be cured without radical surgery unless Mohs is utilized.



Why isn't Mohs surgery performed on all skin cancers?

There isn’t enough time or well-trained Mohs surgeons to treat every cancer that is diagnosed by the Mohs method.  And in many cases, Mohs surgery is overkill.  Many skin cancers are small, non-aggressive, or located in areas of the body where there is a surplus of skin and removing a wider margin is inconsequential.  A well-trained and experienced general dermatologist can handle many skin cancers with standard excision or curettage, and knows which patients may benefit from referral for the tissue-sparing Mohs technique.


What are my chances for cure?

Mohs surgery cure rates have been reported from numerous studies to be around 99% for most skin cancers, and around 95% for recurrent cancers in which previous treatments have failed.  Other methods of treatment show cure rates of around 88-90% for untreated cancers, and dismal cure rates of around 50% for recurrent cancers.


Why is it called Mohs surgery?

In the early 1930’s, a young medical student at the University of Wisconsin named Frederic Mohs was inspired by the idea of curing tumors by complete microscopic evaluation of the surrounding tissue.  His procedure was initially called
Mohs Chemosurgery because zinc chloride was applied to the cancer before removal and checking the margins for clearance. His procedure resulted in dramatic cures in high numbers even for seemingly hopeless tumors.  Later it was discovered that it was really the process of clearing the margin of all cancer cells, and not the topical chemotherapy, that resulted in cure. Because of this, the named was changed from Mohs Chemosurgery to Mohs Micrographic Surgery to emphasize the importance of mapping the tumor to aid in microscopic clearance of all tumor roots.  Dr. Mohs trained as a general surgeon and spent his entire career refining the technique of surgical removal and pathologic examination and publishing his work.  Later, Dr. Mohs began to train other physicians in his method.  General surgeons as a specialty did not embrace the technique because they had no background in pathology or laboratory medicine.  Dermatologists, who have extensive training in dermatopathology and microscopic evaluation, saw the potential of the procedure and began to use it.  Today, Mohs micrographic surgery is recognized as the treatment with the highest cure rates for skin cancer and is performed almost entirely by dermatologists with special training in surgery.