By GINA KOLATA Contrary to popular opinion, sup- port groups do not extend the lives women with advanced breast cancer according to a large study being pub- lished today. The study disputes belief that has been stated so often is almost considered a truism - that the mind influences the course advanced cancer so powerfully that patients can hold off death by getting emotional support in a group. The investigators began their study because they were concerned that many patients felt obligated to join support groups, whether they wanted to or not, to fight their can- cer. Many were convinced of their benefit by a small and inconclusive study published more than a decade ago indicating the groups could sub- stantially prolong patients' lives. So the investigators, led by Dr. Pamela J. Goodwin, a medical oncol- ogist at Mount Sinai Hospital of the University of Toronto, recruited 235 women with advanced breast cancer, assigning 158 to attend support groups and 77 not to attend the groups, for comparison. Those as- signed to support groups had a medi- an survival time of 17.9 months. Those who did not go to the groups had a median survival time of 17.6 months, an insignificant difference.