What is the difference in Mohs surgery vs. excision surgeries?

Mohs micrographic surgery is a tissues sparing technique of tumor excision where margins of the tumor are controlled microscopically at the time of excision to ensure full removal without taking any more tissue that is absolutely necessary – there are no margins of extra tissue taken to ensure that the tumor is gone, it is all confirmed visually with examination of 100% of the margins.An excision takes that extra insurance tissue around the tumor, and those margins are dependent on the type of tumor and its characteristics. These are then examined in a different fashion that looks at about 1% of the tissue margin to get an idea that it is clear, as opposed to the 100% that Mohs visualizes.When you add all of those up, Mohs gives you the highest cure rate of any modality, and it takes the least amount of tissue possible. That means you can be the most confident that your tumor is gone (above a 98% certainty for most tumors), while also knowing that the hole left behind is a small as it could possibly be.Mohs is traditionally reserved for areas where tissue sparing is key on the face, head, neck, hands, and genitals. It is also used when tumors have come back after excision, when tumors are particularly aggressive, or when tumors are particularly large. In those situations, Mohs is the most financially favorable way to take care of those tumors, even though it is more expensive than traditional excision, the outcomes are so much better that the cost ends up being lower in the long run. For all others, traditional excision is a more financially viable option. This is why your insurance made out improve a skin cancer on the arm, trunk, or leg unless it meets Mohs appropriate use criteria.To ensure you are receiving the highest level of care, seek out a modernly trained, new-school dermatologic surgeon, who is board certified and fellowship trained. Cameron Chesnut#realself500 Physician

Great question!  This is a question that comes up frequently in my practice.  Both Mohs and standard excision can be used to effectively treat skin cancers. 

In standard excisions, the visible skin cancer is removed along with a 4-8 mm margin of healthy appearing tissue.  The wound is then stitched closed.  The tissue is then send out for the margins to be checked over the next few days.  When the pathologist looks at the tissue, they use a method called “bread loafing” where the pathologies makes slices through the tissue and examines those margins as a representative sample to determine that the margins are clear.



In Mohs surgeries, the visible cancer is removed along with a narrow rim of healthy tissue.  The tissue is then processed while the patient is waiting in the clinic.  During the processing, the edges are laid down in order to examine 100% of the margins.  It is helpful to compare the Mohs layer of tissue to a pie.  The processing lays down the crust (tissue edges) to make sure there is an intact layer of crust (healthy skin) separating you from the pie filling (or your skin cancer).  If residual cancer is found, then another layer is taken but only if the areas where cancer was seen and the rest of the healthy tissue is left alone.  This method has the highest cure rate, with the smallest amount of tissue removed.  Once the cancer is cleared, then the wound is stitched closed. 



Mohs surgery is a more time consuming and more costly treatment option that is used for areas where tissue conservation is important.  These areas include the face, scalp, neck, hands, feet, genitals and shins.  You should always feel comfortable asking your board certified dermatologist to explain further details about each treatment option and why they specifically recommended that option for you.

Both standard excision and Mohs excision are methods used to remove skin cancers.  In Mohs surgery the pathology is done while you wait.  In standard excision the pathology is done over a few days to a week.Mohs pathology examines more of the margin and thus allows a narrower excision to be checked with high fidelity - ideal in places like the nose or eyelid.  Also because the pathology is clear more complex stitching can be done more comfortably the same day, knowing that a positive margin won't come back a few days later.In less sensitive areas where there is more loose skin and relatively straightforward sewing can be done, the advantages of Mohs surgery over traditional excision is reduced significantly.  A 2-3mm difference in the cancer removal specimen may be very important in the nose but much less important on the arm for example where in either case the wound would be stitched with a straight line for example.  Similarly the difference in cure rates between the two approaches is much less for small superficial lesions on the body or arms.Other treatment options can be used for small superficial lesions.The relative value of each procedure is increasingly being determined by insurance coverage and to insure that Mohs surgery is used primarily in places where it is more beneficial, a series of appropriate use criteria were developed and are used by a number of insurance carriers to determine eligibility for Mohs.  I would advise you to check with your doctor to discuss the pros and cons of each approach for your particular tumor.