WASHINGTON, D.C.: Providing new ammunition for groups who say women should begin having mammograms at age 40, preliminary results from a new study suggest that women who routinely examine their breasts for lumps may not be reducing their risk of dying from breast cancer. Researchers, led by Dr. David Thomas of the Fred Hutchinson Cancer Research Center in Seattle, studied 267,000 Chinese women in Shanghai and enrolled about half, 133,375 in an intensive self-examination program. Thomas said "there was no difference" in the rates of either cancer deaths or in cancer detection, although women who performed the examinations found twice as many benign tumors than the women in the control group. This study is the first to suggest the exams may not make a significant difference. "So far, we don't have a hint that it does any good," Thomas said. "But in order to get a final word on this, we will have to follow this group for five more years." The news comes as a Senate panel is pushing for federal guidelines telling women to begin mammography exams at 40. Although all agree yearly mammograms should start at age 50, current scientific opinion is divided on whether exams between the ages of 40 and 49 are necessary and cost-effective. While this new study doesn't resolve that dispute, it could tilt the balance.