Mohs surgery for basal cell carcinoma / squamous cell carcinoma
Basal cell carcinoma and squamous cell carcinoma are the two most common skin cancer and sun exposed areas such as the face, dorsum of the hands are the common site of these malignancy. If wide local excision is made to prevent from the recurrence, large skin defect may occur on the face or the hands. Mohs surgery allows the patient to save the normal skin as much as possible while removing only the skin cancer. On-site pathology test is done during the surgery and the specimen is examined to see if the cancer is removed completely in the first stage surgery. If there still is malignant cells at the edge of the excision wound, the additional excision is made as the second stage surgery only to the part where the left-over cancer cell is in question. The pathology test is done to this excision specimen, again. The multi-stage excision is continued until the site is proved to be cancer-free pathologically. The reconstruction of the skin defect is performed after the lesion is proved to be cancer-free. The long term (i.e. 5 years) recurrence rate after the excision of basal cell carcinoma is 1% with Mohs surgery, whereas the conventional, wide-local excision method yields much higher recurrence rate (see the table below).
The conventional, wide-local excision method, on the other hand, usually takes 3-10mm margin from the edge of the visible cancer edge. The specimen is sent for the pathology test and takes 7-10 days to examine the residual malignant cells. These specimens are only examined for every 2-3 mm representative sections, therefore not the entire specimen is examined. This is why the recurrence rate of the conventional, wide-local excision is worse than Mohs surgery. In addition to that, the pathology test of the conventional method takes 7-10 days with no guarantee of complete excision until the pathology report. If the pathology report says there is residual cancer cells, the second stage excision is necessary which, again, requires additional 7-10 days until the pathology report is made. If the wound closure or reconstruction is performed before the pathology test result, there is a risk of remaining cancer cells.
Thus, Mohs surgery enables more reliable removal of cancer cells while avoiding the unnecessary removal of normal skin as much as possible. This, in turn, results in better cosmetic appearance and lower recurrence rate in a long run. This method is prevalent in all the Western countries and many other countries, such as South Korea and the Philippines, but is not adopted in other hospitals and clinics in Japan. The reasons for this is partly because the technique requires multi-discipline in dermatology, plastic surgery, dermatopathology, and Mohs laboratory technique, but there is no training center in Japan.
We use cryostat of Leica, that is to cut the frozen specimen into sections, to examine the tissue during Mohs surgery. We collaborate with EMI factory, a precision instruments maker, to cut the frozen section in an appropriate manner, which is the crucial part of accurate pathology diagnosis. Mohs technique is the best surgical method for the patients with basal cell carcinoma and squamous cell carcinoma, who desire to mimimize the skin defect and to obtain the lowest risk of the recurrence.
Five-year Cure Rates for Primary BCC and SCC
|Treatment modality||BCC 5-year cure rate(%)||SCC 5-year cure rate(%)|
Electrodesiccation & curettage
|All non-Mohs modalities||91||92|