Mohs surgery is unique in its precision.  Instead of removing the whole clinically visible tumor and a large area of normal-appearing skin around it, the Mohs surgeon removes the minimum amount of healthy tissue and totally removes the cancer.  Thin layers of tissue are systematically excised and examined under a microscope for malignant cells.  When all areas of tissue are tumor-free, surgery is complete.

The technique has several major advantages.  It preserves more normal tissue than any other method while at the same time allowing the surgeon to trace and eradicate areas of tumor that are invisible to the naked eye.  The Mohs surgeon, after examining the tissue under a microscope, knows exactly how far the tumor extends.  As a result, Mohs surgery is particularly suitable for the area around the eyes, and the nose, ears and mouth where the preservation of normal tissue is essential.  Lastly, when other standard methods have been unsuccessful, Mohs surgery offers another chance for cure.

The procedure does not require general anesthesia, which permits its use on many patients who are poor candidates for conventional surgery.  Since the mortality rate is almost zero, elderly patients in poor heath can be treated safely.  Most patients do not have to be hospitalized and can be managed on an outpatient basis.  The surgery can usually be completed in half a day or less.

Technique

The physician makes a reference map of the whole area to be excised.  A local anesthetic is then injected.  Some Mohs surgeons start with the use of a curette. As each section of tissue around the cancerous site is surgically removed, it is identified on the map by its corresponding number.  The edges of the specimen are dyed blue and red to indicate its specific direction and geographic relation to the other sections - superiorly, inferiorly, medially, and laterally (north, south, east, and west).

Sections of the tissue are removed in stages, and sent to an on-site laboratory for slide preparation and study.  As the tissue is prepared to be viewed by the Mohs surgeon, it is cut, frozen, sliced, placed onto slides and then stained appropriately.  It takes about one hour per stage before the slides are available for the physician to read.

As each section is microscopically examined by the Mohs surgeon, the location of malignant cells is marked in color on the original map of the numbered sections and oriented exactly by the red and blue coding.  If a specific section that has been removed shows evidence of malignancy, another section will be removed in the area where tumor remains.  The procedures of excision, mapping, and evaluation are repeated as often as necessary until the cancerous tissue is completely eradicated.  As few as one or two sections, or as many as a dozen or more, may be removed.  Most Mohs surgery cases are completed in only two or three stages, so the entire procedure is often finished in less than two hours or so.

If possible, the wound will be closed immediately.  It may also be left to heal by itself, a process that usually takes an average of four to eight weeks.  Or it may be repaired with a skin flap or skin graft.  The patient will be asked to restrict physical activity for a day or so and taught how to change the dressing on the wound.

The scar that is left after healing can be corrected at a later date, if necessary.  The body does a wonderful job of improving scars with time.  Therefore, it is often recommended to do the minimum correction over the maximum amount of time.

Recommendations:

Mohs surgery is clearly indicated for recurrent skin cancers, for those in scar tissue, and cancers in an area such as the face, where preserving tissue for a good cosmetic result is desired. The procedure is also preferred when the cancer is extensive and grows very quickly, or when it is difficult to determine the extent of the lesion.