Palo Alto, Calif. ? Contradicting an old belief, new research released Sunday found that group therapy didn’t prolong the lives of women with advanced cases of breast cancer.

The report in the journal Cancer found support groups improved patients’ quality of life and had beneficial effects on mood and pain, but it undercut what had been seen as the greatest potential benefit.

In 1989, a landmark study found that group therapy doubled the lives of women with metastatic breast cancer, a finding that spurred proliferation of cancer support groups and fueled a debate about the effect of psychology on the course of cancer.

Stanford University psychiatrist David Spiegel, who led both studies, said cancer treatments had improved in the past two decades, making it possible for most patients to live longer without psychotherapy.

Spiegel said the latest study shouldn’t discourage cancer patients from joining support groups, which count thousands of people as members and have become an accepted part of cancer care. The groups encourage participants to express fears, anger and depression, confront their doctors and grieve those in the group who have died.

Dr. David Kissane, chairman of psychiatry and behavioral sciences at Memorial-Sloan Kettering Cancer Center in New York, who was not connected to the study, said the latest report should end the decadeslong debate.

“Group therapy is a great help to women, but it is time to debunk the myth that it extends survival,” he said. “It does not.”

Spiegel said that social attitudes about cancer have become more accepting, making it possible for patients to find social and emotional support outside of group therapy. So the effect of group therapy may be less powerful today that it was 30 years ago when “cancer was a dirty word,” he said.

“People saw it as a death sentence, and they suffered in silence,” he said.

Mitch Golant, a psychologist and vice president of research and development for the Wellness Community, a nonprofit organization that sponsors support groups, didn’t expect the study to affect participation.

“The No. 1 reason why people join support groups is because they want to be with others who are going through what they are going through,” he said.

Patients acquire better coping skills, he said, and benefit from lower levels of stress and anxiety.

“It is great to live longer, but these patients also want to live better,” he said.