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But such surgery did not improve survival in a group of nearly 500 patients with very small tumors, according to findings scheduled for presentation Saturday at the annual meeting of the American Society of Clinical Oncology (ASCO), in Chicago.
"I think that our study is the beginning of the end of a general recommendation of complete lymph node dissection for patients with positive sentinel nodes," senior study author Dr. Claus Garbe, a professor of dermatology at the University of Tubingen in Germany, said in an ASCO news release.
However, patients with advanced melanoma likely will continue to need all of the surrounding lymph nodes removed, as that is a well-established strategy for improving their survival, said Dr. Vernon Sondak, chief of cutaneous oncology at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Fla.
"Surgery is critical in those more advanced cases," said Sondak, who was not involved in the new study.
But these findings suggest that some patients whose melanoma has been caught early might be able to avoid the surgery, if they agree to rigorous ongoing observation of their condition, Sondak said.
When a person is diagnosed with melanoma, doctors take samples from nearby lymph nodes to see if the cancer has spread, according to the American Cancer Society. This procedure is called a sentinel node biopsy.
If one of the lymph nodes has cancer, doctors perform more extensive surgery to remove all of the lymph nodes surrounding the tumor. The thought was that melanoma can spread throughout the body via the lymph nodes, and their removal would keep the cancer in check and improve survival, said Dr. Lynn Schuchter, a melanoma specialist at the University of Pennsylvania's Abramson Cancer Center.
But doctors now suspect that melanoma can spread without going through the lymph nodes, and that removing the glands may be unnecessary for some patients, said Schuchter, who played no role in the new research.
Removal of large groups of lymph nodes carries the risk of debilitating side effects, including infection, nerve damage and lymphedema -- an uncomfortable condition in which legs or arms swell because the lymph nodes aren't there to transport fluid away from the extremities.
Lymphedema can occur in more than 20 percent of patients, and persist long-term in up to 10 percent of patients, the study authors said.
"Many patients already have been deciding not to have their lymph nodes removed, because of the concerns associated with lymphedema," Schuchter said.
In the new study, 483 patients with stage 3 melanoma -- meaning the cancer had begun to spread -- and a positive lymph node biopsy had their primary tumor removed. They then were randomly assigned to observation only or removal of all nearby lymph glands.
During follow-up, in which half the patients were monitored for more than three years, the cancer had spread in 14.6 percent of patients in the observation group, compared with 8.3 percent in the group that had additional surgery to remove lymph glands.
But no statistically significant improvement in survival occurred between the two groups at three years or five years, the researchers reported.
"Doctors may want to discuss this finding with their patients to help them decide whether this procedure is right for them," Garbe concluded.
Only patients with tiny, microscopic-size tumors were included in this study, the researchers said. Garbe agreed with Sondak that people with larger tumors still will need full removal of nearby lymph nodes.
Schuchter said this study suggests a new "maybe less is more" approach to cancer treatment.
"The trend has been to try to do the right surgery, and sometimes that means less surgery because of the complications associated with surgery," she said.
She noted that data from larger trials in breast cancer patients already found no benefit in removing all nearby lymph nodes.
"Women with breast cancer now are not getting complete lymph node dissection," Schuchter said. "I think we're going to learn a similar lesson in melanoma."
Studies presented at meetings are usually considered preliminary until published in a peer-reviewed medical journal.
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SOURCES: Vernon Sondak, M.D., chief, division of cutaneous oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Fla.; Lynn Schuchter, M.D., melanoma specialist and chief, hematology/oncology, University of Pennsylvania Abramson Cancer Center, Philadelphia; presentation abstract, American Society of Clinical Oncology annual meeting, May 30, 2015, Chicago, Ill.