Role of SLN biopsy for thin melanomas unclear.

WAIKOLOA, HAWAII -- The role of sentinel lymph node biopsy in patients with thin melanomas is "an enormous conundrum," Dr. Daniel G. Coit observed at the annual Hawaii dermatology seminar sponsored by Skin Disease Education Foundation.

"The significance of a positive sentinel lymph node in thin melanomas is totally unknown. It's not at all clear that a positive sentinel node portends a poor prognosis in patients with thin melanoma. This we need to discuss with our patients, and these are often very lengthy discussions," said Dr. Colt, a surgeon who is coleader of the melanoma disease management team at Memorial Sloan-Kettering Cancer Center, New York, and a member of the American Joint Committee on Cancer's melanoma staging committee.

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Thick or intermediate melanomas are an entirely different matter. Numerous studies have convincingly established that sentinel lymph node biopsy (SLNB) is a very important prognostic tool in patients with such lesions. In the setting of T2-T4 melanomas, a positive SLNB is clearly associated with significantly reduced disease-free survival and other key outcomes, he said.

But for thin melanomas--those 1.0 mm or less--there are no good prospective data showing SLNB has prognostic value. And that is a major problem because, in the modern era of improved early detection, thin melanomas are extremely common. At Sloan-Kettering, for example, 55% of all patients presenting for primary treatment of melanoma have thin lesions, he noted.

Some useful but somewhat retrospective data regarding the predictors and prognostic significance of SLNB positivity come from a study by Dr. Coit and coinvestigators. They evaluated 223 patients in the prospective Sloan-Kettering database who underwent wide excision with SLNB for thin melanomas.

Only 3.6% of patients had a positive SLNB, a rate less than one-fourth that typical with intermediate-thickness tumors. All eight patients with a positive SLNB had tumors that were both Clark level IV and 0.75-1.0 mm thick. In other words, the rate of SLNB positivity was zero in patients with tumors that were Clark level II/III or less than 0.75 mm thick. Interestingly, the only deaths in the first years of follow-up were in SLNB-negative patients (Ann. Surg. Oncol. 2006;133:302-9).

"This study doesn't tell you whether or not you have to do a sentinel node biopsy. It begins to present reasonable estimates of the probabilities of finding a positive sentinel lymph node. [Patients] will tell you what their threshold is for wanting to go ahead with it," Dr. Coit said.

Widespread misconception surrounds the true purpose of SLNB in melanoma. "If the goal of sentinel lymph node biopsy is to help predict outcome, it's a very, very good tool. But if you take a large number of patients and randomly assign them to sentinel node biopsy or observation, there is absolutely no difference in overall survival.... It is enormously important that patients understand they are not having it to live longer," the surgeon continued.

This point was persuasively brought home in the landmark Multicenter Selective Lymphadenectomy Trial, which showed that SLNB didn't affect disease-free or melanoma-specific survival (N. Engl. J. Med. 2006;355:1307-17).

Do all melanoma patients with a greater than 1-mm-thick primary tumor and a positive SLNB require completion lymph node dissection? That's the current standard practice, but a study by Dr. Coit and associates casts doubt upon it.

They gathered 134 melanoma patients from Sloan-Kettering and 15 other melanoma centers around the world. All 134 had a positive SLNB but did not undergo completion lymphadenectomy, while a control group comprised 164 matched patients who did have lymphadenectomy. With a median follow-up of 20 months, there was no significant difference between the two groups in nodal recurrence rates or overall survival (Ann. Surg. Oncol. 2006;13:809-16).

Dr. Allan C. Halpern, chief of the dermatology service at Sloan-Kettering, observed that another common misconception regarding SLNB is that a negative result confers an good prognosis.

"I can't tell you how often dermatologists will call me up, amazed that they have a patient with a melanoma less than 1 mm thick who's now 5 or 6 years out and has metastatic disease.... The truth of the matter is, if you look at the 10-year survival in that group, it's about 90%, which means about 10% of them do go on to develop distant metastatic disease and die," Dr. Halpern said.

"We have to be careful, especially in interpreting negative sentinel lymph nodes. A negative sentinel lymph node does not mean excellent survival. That's why there are all those other stages, from I to IIb, and stage IIb disease is very serious disease," he stressed.

SDEF and this news organization are wholly owned subsidiaries of Elsevier.

BY BRUCE JANCIN

Denver Bureau