Women in their 40s who received annual mammography screening do not have a better chance of surviving breast cancer than those who received usual care from their personal physician, report University of Toronto researchers in the Canadian National Breast Screening Study-1.
"After an average 13-year follow-up, our research shows no mortality benefit from mammography screening in this age group in spite of the fact that mammography diagnosed far more cancers," says Dr. Anthony Miller, a professor emeritus in the Faculty of Medicine's public health sciences department and lead author of the study in the Sept. 3 issue of the Annals of Internal Medicine. "This is the only trial to date specifically designed to evaluate breast screening among women aged 40 to 49."
The study involved 50,000 volunteers in their 40s, recruited from 1980 to 1985, who were not pregnant, had no previous breast cancer diagnosis, and had not had a mammogram in the previous 12 months. Participating at 15 screening centres across Canada, the women were randomly assigned to one of two groups - 25,214 received four or five annual mammography screenings and breast physical examinations and 25,216 women received a single breast physical examination followed by usual care from their personal physician. Both groups were instructed on breast self-examination.
In the study, physicians provided breast physical examinations in three centres in Quebec and nurses in the 12 remaining centres. The physicians and nurses also taught and evaluated breast self-examination while conducting their own examination. Two-view mammography was done on dedicated mammography units.
Cancer detection was higher with mammography than in the group screened by physical examination alone - 87 versus 58 cases at the first screening exam. After 13 years of follow-up, 592 women in the mammogram group were diagnosed with invasive breast cancer compared to 552 in the usual care group. As of 1996, 105 women in the mammography group had died of breast cancer versus 108 women in the usual care group.
"The data from this research are quite striking and quite clear," says Dr. Cornelia Baines, professor in U of T's public health sciences department and a co-author of the study. "The difference between annual screening compared to the control group is not statistically significant. Breast cancer mortality was not reduced."
The study's other authors are Dr. Teresa To, of public health sciences and population health sciences at The Hospital for Sick Children and Claus Wall of public health sciences and the Institute for Clinical Evaluative Sciences.
Funding for the study was provided by the Canadian Cancer Society, the Department of National Health and Welfare, the National Cancer Institute of Canada, the Alberta Heritage Fund for Cancer Research, the Manitoba Health Services Commission, the Medical Research Council of Canada, le Ministere de la Sante et des Service Sociaux du Quιbec, the Nova Scotia Department of Health, and the Ontario Ministry of Health. More recently, the follow-up has been supported by the Canadian Breast Cancer Research Initiative. Miller was supported in part by a National Health Scientist Award from the Department of National Health and Welfare of Canada.
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