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.
| 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
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