Chapter 53 Mohs surgery
1. What is Mohs surgery?
In 1936, Dr. Frederic Mohs, of the University of Wisconsin, developed a precise tumor extirpation technique that involved the controlled, serial, microscopic examination of tissue that had been chemically fixed with zinc chloride paste. The excised tissue was systematically mapped, frozen sections were examined, and the process was then repeated at foci of residual malignancy until a completely tumor-free plane was reached. The goals of Mohs surgery are to completely remove the tumor and to maximize tissue conservation.
2. Is Mohs surgery still performed with the zinc chloride chemical paste?
Very rarely. The technique has evolved to use fresh frozen tissue methods. In the 1970s, the use of frozen sections alone in Mohs surgery was shown to have comparable cure rates to the use of zinc chloride paste. The elimination of zinc chloride paste allowed Mohs surgery to take place in a single day and avoided the pain associated with paste application. In addition, the use of frozen sections made it possible for reconstruction of the Mohs defect to occur the same day as tumor removal.
3. When is Mohs surgery indicated for basal cell and squamous cell carcinoma?
Mohs micrographic surgery is especially effective in treating basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) of the face and other cosmetically sensitive areas, because it can eliminate the cancer while sparing surrounding normal skin. It is also ideal for the removal of recurrent skin cancers. In these tumors, cancer cells persist in areas of scar tissue, and the clinical margins of the recurrent tumor are often indistinct. Cure rates are 99% for primary basal cell cancers and 95% for recurrent tumors. Other indications for Mohs’ surgery include
• BCC with aggressive histopathologic features, such as morpheaform or sclerotic (desmoplastic), micronodular, superficial spreading, and infiltrative growth patterns, subtypes which often extend beyond visualized margins
• Primary BCC or SCC with poorly defined borders, especially those present in locations known to have high recurrence rates (nasolabial fold, nasal ala, medial canthus, pinna, and postauricular sulcus)
• Any location where maximum preservation of normal tissue is paramount (e.g., nasal tip, nasal ala, lips, eyelids, ears, genitalia, fingers)
4. Is Mohs surgery appropriate for all basal and squamous cell carcinomas?
BCC and SCC are epidemic in the United States. Standard treatments, including excisional surgery, electrodesiccation and curettage, cryosurgery, and radiation therapy, have cure rates in selected series near 90%. Mohs surgery should usually be limited to indications outlined in Question 3, due to the time and expense required by the procedure.
5. In addition to basal cell and squamous cell carcinoma, what other cutaneous tumors can be treated with Mohs surgery?
Almost any type of cutaneous tumor that grows in a contiguous fashion can be treated with Mohs surgery. The technique has been found to be particularly effective for aggressive cutaneous tumors that often recur after conventional excision. Cutaneous tumors that have been demonstrated to have high cure rates with Mohs surgery (90% to 100%) include
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