The most important thing to remember about the Mohs procedure is that it is a precise surgery that spares healthy tissue and removes the cancer completely, in one sitting. The standard excision aims to remove the cancer completely but the excision size is an "over- estimate" that includes the surrounding normal tissue in order to prevent re-excisions.
Below is a comparison chart of the standard excision and Mohs excision. Images below also compare the relative size of tissue trauma resulting from each procedure.
|Standard Excision||Mohs Excision|
|One large piece of tissue is removed all at once||Small amounts of tissue are removed in stages|
|Wound is stitched up and patient is sent home to wait for results||Wound is left open until all of the excised tissue is evaluated and removed the same day|
|Size of excision is an estimate, must be larger than tumor to have clear margins, large amount of healthy tissue is removed||Excision is precise and healthy tissue is spared|
|Orientation is less accurate||Precise orientation of tissue is maintained through the entire process|
|3-5 mm margins||1-2 mm margins|
|Scar is larger||Scar is smaller|
|Tissue is fixed in formalin for paraffin processing; evaluation may not be done for several days ||Tissue is frozen and cryosectioned for rapid evaluation|
|About 1% of the margin is evaluated, depending on the grossing protocols||100% of the margin is evaluated|
|If original excision shows tumor in the margins, a new excision must be made around the scar ||Excisions are continued in stages until all of the affected tissue is removed; no re-excisions needed |
|Skin cancer cure rate 89-92% ||Skin cancer cure rate above 98% |
|May have adverse effects on function and cosmesis ||Preserves function and cosmesis of area|
|Tissue is paraffin processed for permanent sections||Tissue is fresh and frozen-sectioned, no tissue is retained (typically) for permanent sections|