SAN DIEGO The use of the Mohs technique for melanoma is probably limited to those with a Breslow thickness of 1 mm, because in melanomas thicker than that, sentinel node biopsy takes precedence, Dr. Kenneth Gross said at a meeting sponsored by the American Society for Mohs Surgery.
Much of the important work establishing the safety of the Mohs approach in melanoma has been done by Dr. John Zitelli of Pittsburgh, said Dr. Gross, who practices surgical dermatology in San Diego.
In studies with 5-year follow-up on patients, Dr. Zitelli has shown that recurrence rates and mortality using a Mohs technique are equivalent to, or better than, those of historical controls treated with conventional surgery using recommended margins.
However, for those melanomas with a Breslow thickness of between 1 mm and 3.5 mm, surgical oncologists like to know the results of a sentinel node biopsy, Dr. Gross noted. The reason they do is that the Multicenter Selective Lymphadenectomy Trial showed that this could be very important in intermediate thickness lesions. Five-year survival among those individuals in the trial who were found to have positive nodes was 72% when patients had immediate lymphadenectomy, but only 52% when the lymphadenectomy was delayed (N. Engl. J. Med. 2006;355:130717).
Dr. Gross said when he performs Mohs on a patient with melanoma he is careful to obtain a detailed consent from the patient. He also uses a Wood's lamp and magnification before and during the procedure to be sure he is seeing all it is possible to see.
When removing and sectioning a melanoma, Dr. Zitelli often takes the tumor plus about a 3-mm margin in the first stage, and he takes the specimen all the way down to the fat, Dr. Gross said.
Dr. Gross said he takes sections slightly larger than standard, and once he believes he has a clear margin, he removes another 45 mm which is sent for permanent sectioning. He also has a pathologist reading his slides with him.
What constitutes a clear margin has been defined by Dr. Zitelli as a margin that does not have three or more unusual melanocytes or melanocytes above the dermal-epidermal junction.
Dr. Gross said that he often uses Mohs zinc chloride paste, applying the escharotic agent to the lesion the night before the surgery is to be performed, and that he also often uses the MART-1 (melanoma antigen recognized by T-cells 1 staining) immunostain.
Because he takes a fairly large margin around the melanoma lesion when he makes his first Mohs excision, 90% of his melanoma cases are cleared on the first stage, Dr. Gross said.