Annual mammograms do not lower breast cancer deaths in women aged 50 to 59 who are also receiving professional breast physical examinations and have training in breast self-examination, say University of Toronto researchers reporting on the Canadian National Breast Screening Study-2 (CNBSS).
"After an average follow-up of 13 years comparing two groups of women aged 50-59- one group receiving annual mammograms and breast physical examinations and the other physical examinations alone- we've found that breast cancer mortality is almost identical in the two groups," said Dr. Anthony Miller, a professor emeritus in the Faculty of Medicine's department of public health sciences, director of the CNBSS and lead author of the study published in the Sept. 20 issue of the Journal of the National Cancer Institute. "This is the first long-term screening trial to investigate the benefits of mammography over and above breast physical examinations. All other trials have compared the effectiveness of mammogram screening to no screening at all."
The trial involved almost 40,000 women in their fifties who volunteered to participate at 15 screening centres across Canada. From 1980 to 1985, the researchers randomly assigned 19,711 women to the combined mammogram/examination group and 19,694 women to the physical examination-only group. This ensured an equal distribution of demographic variables and breast cancer risk factors in each group. All women were taught breast self-examination.
Over the screening and follow-up period, 622 women were diagnosed with invasive breast cancer in the combination group and 610 in the physical examination-only group. As of 1996, 107 women in the combination group had died of breast cancer compared to 105 in the physical examination-only group.
"We are not discounting the value of screening mammograms compared to no screening at all, but we are saying that effective and regular breast physical examinations with breast self-examination are an alternative to annual mammograms for women in their fifties," said co-author Dr. Cornelia Baines, professor in U of T's department of public health sciences and deputy director of the CNBSS. "This option may be of particular value for women in countries where mammography is inaccessible. But it should also be taken into consideration by physicians and public health professionals in North America and Europe-careful, thorough professional breast examinations along with training in breast self-examination are invaluable for women. However it is important to realize these observations apply only to screening and not to diagnostic mammography."
The researchers also noted that the professional breast screening examinations in this trial were more detailed, focusing on subtle signs of cancer-both visible and palpable- than some breast physical examinations currently performed by health professionals.
In the CNBSS nurses performed approximately 70 per cent of the physical examinations with the remainder performed by physicians. All of the trial's screening centres used two-view, low-dose film-screen mammography. For quality control, a reference radiologist was appointed to review random samples of mammograms.
The study's other authors are Teresa To of public health sciences at U of T and population health sciences at the Hospital for Sick Children and Claus Wall of public health sciences at U of T and the Institute for Clinical Evaluative Sciences.
Funding for the study was provided by the Canadian Breast Cancer Research Initiative, the Canadian Cancer Society, Health and Welfare Canada, the National Cancer Institute of Canada, the Canadian Institutes of Health Research, the Alberta Heritage Fund for Cancer Research, the Manitoba Health Services Commission, le Ministère de la Santé et des Services Sociaux du Québec, the Nova Scotia Department of Health and the Ontario Ministry of Health.
Journal
JNCI Journal of the National Cancer Institute