The recently published results from the Canadian National Breast Screening Study have caused controversy over the use of mammograms for breast cancer screening purposes. The results of the 25-year study, published in the British Medical Journal, February 11th, 2014, concluded that annual mammography does not reduce the mortality from breast cancer. This has caused a polarization of opinions in the debate over the usefulness of breast screening.
The Canadian National Breast Screening Study was conducted across 15 screening centers in 6 Canadian provinces from 1980-1985. Just under 90,000 women aged between 40-59 years participated in the study, and were randomly divided into the intervention group (mammography screens), or control group (no mammography screens).
The study reports that of the 44,925 participants in the mammography arm, 666 were diagnosed with invasive breast cancer, of which 180 died from the disease. Similarly, of the 44,910 participants in the control arm, 524 were diagnosed with invasive breast cancer, of which 171 died from the disease. The study concluded that annual mammography does not reduce mortality from breast cancer. An interesting finding that the study did point out was that there was an over-diagnosis of breast cancer (by 22%) in the mammography arm, resulting in treatment of cancers that were not likely to have been fatal, and therefore, women who received surgery or therapy that they did not need.
The results of the Canadian National Breast Screening Study did show a significantly higher survival rate for women in the mammography arm (70.6%) compared with women in the control arm (62.8%). The authors, however, state the differences are likely due to lead time, length time bias and over diagnosis, rather than an actual difference in survival.
In light of the recent study, there are those who would advocate that breast screening has not reduced the death rate from breast cancer, and is therefore not effective. In addition to the cost of screening, there is the added cost of un-necessary treatment of over diagnosed cancers to consider.
There are others, who are claiming that the study is flawed due to the use of obsolete mammography machines from the 1980’s. The technology available is much better today, and more recent studies, using this current technology, have demonstrated reduced breast cancer deaths with mammogram screening.
While the debate will continue over the results, the current recommendations according to The American Cancer Society are:
- Yearly mammograms are recommended starting at age 40 and continuing for as long as a woman is in good health.
- Clinical breast exam (CBE) about every 3 years for women in their 20s and 30s and every year for women 40 and over.
Miller AB, Wall C, Baines CJ, Sun P, To T, Narod SA. “Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial” BMJ 2014; 348:g366 (Published 11 February 2014).
American Cancer Society Guidelines for the Early Detection of Cancer. Available from: http://www.cancer.org/healthy/findcancerearly/cancerscreeningguidelines/american-cancer-society-guidelines-for-the-early-detection-of-cancer Last Accessed: Feb 14, 2014.
Written by Deborah Tallarigo