MAUI, HAWAII Evidence from randomized clinical trials indicates that excision margins of 2 cm are optimal for primary melanomas greater than 2 mm thick, Dr. Merrick Ross said at the annual Hawaii Dermatology Seminar sponsored by Skin Disease Education Foundation.
That's good news for patients, because 90% of surgical defects resulting from a 2-cm-wide excision margin on the trunk or a proximal extremity can be closed primarily without grafts, noted Dr. Ross, Charles McBride Professor of Surgery and chief of the melanoma section at the University of Texas M.D. Anderson Cancer Center, Houston.
"The take-home message is we probably don't need wider margins than 2 cm for any melanoma. But we shouldn't be cavalier about our margins of excision because very narrow marginsparticularly 1 cm for the thicker melanomasmay not be adequate and will have a negative impact on the natural history," he said.
Empirically based 5-cm excision margins were standard for most of the 20th century. Beginning in about 1970, however, surgeons began to adopt narrower margins for thinner melanomas with good clinical results.
The contemporary era of evidence-based excision margins rests upon five prospective randomized trials that attempted to define the margins, optimizing the chance for durable local control while minimizing surgical morbidity and cost.
These trials established 1-cm margins as the standard for thin melanomas, defined as those with a Breslow's depth of invasion of less than 1 mm. For tumors measuring 12 mm in thickness, the trials suggested margins of 12 cm.
The 2-cm margins for melanomas thicker than 2 mm favored by Dr. Ross and other surgical oncologists were arrived at by examining the results of two complementary randomized trials. One was an as-yet-unpublished study by the Swedish Melanoma Study Group that randomized 644 patients with such melanomas to wide excision with either 2- or 4-cm margins. Rates of locoregional recurrence or death from melanoma proved no different in the two groups (SKIN & ALLERGY NEWS, December 2005, p. 36).
The other relevant trial was conducted by the United Kingdom Melanoma Study Group. In that trial, 900 patients with melanoma measuring at least 2 mm in thickness were randomized to 1- or 3-cm excision margins. The 1-cm group had a 26% increased relative risk of locoregional recurrence during a median 60 months of follow-up (N. Engl. J. Med. 2004;350:75766).
"For lesions thicker than 2 mm, a 3-cm margin is better than 1 cm based on the U.K. trial in terms of locoregional events," he said. But based on the Swedish trial, if a 4-cm margin is not better than a 2-cm margin, then a 3-cm margin can't be better than a 2-cm margin. "So by default, our standard is a 2-cm margin," Dr. Ross explained.
The standard margin for melanoma in situ is 5 mm. Unlike the recommendations for true melanoma, the standard for melanoma in situ is not based upon prospective randomized trial data. It's simply accepted practice based upon extensive clinical observation and experience indicating that the risk for local recurrence is extremely low with 5-mm margins. This sets a precedent that may be relevant to the future status of Mohs surgery for melanoma, he continued.
Critics of Mohs for melanoma argue it is not the standard of care and is unlikely to offer a cost advantage over standard excision, so therefore it should be evaluated in a randomized trial before gaining acceptance.
"I'm not convinced that's true," Dr. Ross said. "First of all, that trial is never going to be done. Second, we didn't use randomized clinical trials to set standards for melanoma in situ. Once we get a body of literature that's very robust and shows very good outcomes for Mohs surgery, it may become a standard of care."
He predicted that Mohs will be a niche procedure in melanoma. It is most likely to prove advantageous for thin melanomas in anatomically difficult locations, such as the head and neck, as well as for lentigo maligna melanoma, in which subclinical disease is often present at a considerable distance from the primary tumor.
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'The take-home message is we probably don't need wider margins than 2 cm for any melanoma.' DR. ROSS