Mohs Procedure versus Standard Excisions

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Mohs Procedure versus Standard Excisions

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 ExcisionMohs Excision
One large piece of tissue is removed all at onceSmall 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 removedExcision is precise and healthy tissue is spared
Orientation is less accuratePrecise orientation of tissue is maintained through the entire process
3-5 mm margins1-2 mm margins
Scar is largerScar 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 protocols100% 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

Upper lip ellipse
Upper lip Mohs procedure, stage 1