Register for Study Challenges Mammogram Effectiveness in Breast Screening; Radiologists' Group Dismisses Findings
Breast CancerOctober 5-12, 2000
(NewsRx.com) -- 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 September 20, 2000, 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 American College of Radiology, however, dismissed the study as flawed.
The trial involved almost 40,000 women in their fifties who volunteered to participate at 15 screening centers 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% of the physical examinations with the remainder performed by physicians. All of the trial's screening centers used two-view, low-dose film-screen mammography. For quality control, a reference radiologist was appointed to review random samples of mammograms.
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 Ministere de la Sante et des Services Sociaux du Quebec, the Nova Scotia Department of Health, and the Ontario Ministry of Health.
The American College of Radiology says the Canadian study is badly flawed because it is based on poor quality mammograms that were read by radiologists with no specific training in mammography and because of the basic design of the study.
The ACR, in leveling this strong criticism at the study, said the study authors used the same flawed methods in following women 50-59 as they did in a previously published, highly criticized study of women 40-49.
In firmly rejecting the current study's conclusions, the ACR urged women to continue to have mammography screening every year, starting at age 40. For the first time in 40 years, and for the past several years in a row, as reported by the U.S. National Cancer Institute, breast cancer death rates have declined, in large part due to increased use of screening mammography, the ACR said.
"It would be tragic if women were persuaded not to have screening mammography based on the highly questionable results of this latest Canadian National Breast Screening Study-2 (CNBSS-2)", the College said. Other, well conducted, screening trials have documented that mammography does indeed save lives.
In addition to major quality issues, the study design, involving volunteers, cannot be used to draw conclusions about a general population, the ACR said. The authors correctly point out that the death rate in their control group is far lower than in the average Canadian population. This was also true in their previously published study of women ages 40-49, where the control group did not have repetitive screening. Their greater than 90% five-year survival among women ages 40-49 strongly suggests a randomization imbalance, according to the ACR.
In the newly released study of women 50-59, the extremely small percentage of lymph node positive cancers (13%) among women receiving only the Clinical Breast Examination (CBE) is unheard of in any other study raising additional concerns about the allocation of patients in the study groups, the ACR stated. The extremely low mortality rate of 105 women of 610 patients (17%) at 10 years among this same group of women is also unprecedented, the group said.
The ACR said another major flaw of the study also pertains to the study design. The authors' original bias is evident in the fact that, instead of comparing the benefit of clinical breast examination in addition to mammography to mammography alone, as one would expect with the "gold standard of care," the investigators asked whether mammography added any additional information to clinical breast examination.
The most recent data confirm the poor quality of mammography screening in the Canadian study. In virtually every other comparison of palpable mammography detected cancers, the majority of cancers are detected by mammography alone. Most are non-palpable, even in retrospect, said the ACR.
In CNBSS-2, almost as many cancers are detected by clinical examination alone as by mammography and clinical breast examination, although there were more cancers expected from high quality mammography.
What is not understood by many who will read these results, pointed out the ACR, is that there was no special training provided for the radiologists reading these mammograms. Mammography screening was not commonly being performed in the early 1980s and radiologists did not have a great deal of experience in interpreting the studies.
Offers by skilled radiologists to train the CNBSS radiologists were turned down, according to the ACR. On the other hand, individuals who performed the clinical breast examinations in the CNBSS were reported to be highly trained and skilled.
In addition to strongly criticizing the CNBSS-2 study, the ACR questioned why the Journal of the National Cancer Institute published such a controversial paper without an accompanying editorial.
This article was prepared by Women's Health Weekly editors from staff and other reports.
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