Following the recent Canadian study published about mammography screening I remain convinced that young women should strongly consider mammographic screening on an annual basis.
Mammography Screening Studies
The recent Canadian study on mammography screening has sparked a major controversy. On the surface, it was an impressive study that included more than 50,000 women who were followed for 25 years.1 It concluded that women between the ages of 40 and 49 receive no benefit from mammographic screening.
These findings are in direct contrast to a larger study from Sweden, which demonstrated a major survival advantage for women in the same age group who underwent routine screening.2
The question is which study to believe. One compelling explanation for the different findings in the two studies is provided by Dr. Daniel Kopans, a recognized authority in mammography from Harvard Medical School.3
Dr. Kopans points out that the Canadian study was biased because it assigned more women with advanced breast cancer to the arm of the study that provided a mammogram as opposed to the second arm of the study in which women were not given a mammogram. In his own words:
“The major problem is that the assignment to one or the other groups was not random, which is a major flaw in study design. It violated the most fundamental requirement of a randomized trial: blinded randomization. They examined everyone so that they knew who had advanced cancers before allocation. They then assigned women on open lists so that a line could be skipped to ensure that a woman with advanced cancer would be placed in the mammography group.”
In addition, Dr. Kopans notes other basic flaws in the study, such as:
- Out of date mammography equipment
- Poor imaging quality
- Insufficient training and supervision of technicians
- Lack of specialty training of mammographers
There is, of course, no such thing as a perfect study. One of the major problems in designing a study with the complexity of the Canadian study is the issue of bias. Dr. Kopans, for example, believes mammography screening saves lives, and it is important to recognize this bias when evaluating his comments.
What might be the biases of the Canadian government in funding a study that is designed to evaluate screening mammography? Certainly, their main objective was to determine if screening mammography had a life-saving value. In other words, is it worth it to invest limited medical resources into what is considered to be an “unproven” approach to breast cancer detection?
Dr. West’s Conclusions
My conclusion is that there was an inherent bias in the design of the Canadian study, which was based on a subliminal desire to reduce costs in a medical system with strict budgetary limitations.
I base this conclusion on the fact that women with clinically evident breast cancer were included in a study supposedly designed to evaluate the effectiveness of screening mammography. By definition, screening is for women without symptoms. The inclusion of women with clinically evident breast lumps and/or enlarged axillary lymph nodes is inappropriate.
The nurses who were in charge of placing patients into mammography versus the no mammography arms of the study were aware that women assigned to the mammography group were more likely to receive timely medical care.
It would be unethical for a nurse who was making this decision to assign a patient with a suspected cancer into a group in which treatment would be delayed. In essence, the design of the study ensured that mammography screening would fail to reduce breast cancer mortality.
The report on the Canadian study comes at an inopportune time. Major progress has been made in the past decade in detecting small and potential curable cancers in young women.
Mammography techniques have been refined and new technologies such as 3-D mammography, screening ultrasound and MRI are now available to detect small cancers that were not detectable with older technology. Detecting these small cancers improves survival and reduces the need for chemotherapy and for more radical surgery.
The application of these newer technologies will not only save lives but, in the long run, reduce medical costs since the cost of treating advanced breast cancers far outweighs the costs of care when breast cancers are detected at an early stage.
1.Miller AB,et. al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomized screening trial. BMJ 2014; 348:g366.
2.Tabar L, et. Al. Mammography service screening and mortality in breast cancer patients: 20-year follow-up before and after introduction of screening. The Lancet 04/2003; 361(9367):1405-10.
3.Kopans DB, Feig SA. The Canadian National Breast Screening Study: A Critical Review. Am J Rad. 1993;161:755-760.