Catherine A. Young, MD
Radiologist with Austin Radiological Association (ARA)
Attacks against screening mammography continue to be reported in the media, typically in reliance on flawed studies or analyses. Most recently, an article in the British Medical Journal (BMJ) questions the value of screening mammography by revisiting data from the Canadian Breast Cancer Screening Study (CNBSS). The CNBSS trial was conducted over 30 years ago and has been widely discredited due to poor quality mammography and lack of proper randomization.
Other, more credible randomized controlled trials (RCTs), as well as many observational studies, have shown that screening mammography does in fact save lives. Moreover, they have shown that the greatest number of lives is saved when screening begins at age 40.
Consequently, leading U.S. healthcare organizations that have analyzed the best available evidence from all sources unanimously recommend regular screening mammography to reduce breast cancer mortality. This includes the American Congress of Obstetricians and Gynecologists (ACOG), National Comprehensive Cancer Network (NCCN), American Cancer Society (ACS), American College of Radiology (ACR), Society of Breast Imaging (SBI), and US Preventative Services Task Force (USPSTF).
A recent article in the journal, The Oncologist, compares screening for breast cancer to having a smoke detector in the house:
You spend some money to install the detector (cost and time invested in screening). For most people, there will never be a fire in the house (only about 12% of women will develop breast cancer). If you are lucky in that way, then after the fact, you can think of the investment in the smoke detector as a waste of money. It is also possible that a fire will start and the detector will not go off for some reason (sensitivity of mammography is approximately 80%) or that the fire gets large so quickly that the alarm does not really help you (a fraction of cancers are too aggressive for screening to be useful). Alternatively, the fire might start in the fireplace, so it does not really matter that the alarm went off because the fire would not have hurt you (some cancers are indolent; these are the overdetected cancers). The alarm might sound in the middle of the night and wake you up, but there is no fire (false-positive screening examinations). The benefits, of course, are that the alarm could wake you up just in time and save your life (mortality reduction attributable to screening) or could even wake you so quickly you can extinguish the fire before any real damage has been done to your house (morbidity and mortality reduction). The equivalents of all these situations occur with mammography screening.
Despite the limitations described, we buy smoke detectors not because we expect a fire but because, by making a modest investment and incurring a certain level of nuisance, we reduce the risk of dying in a fire. The benefits to an individual are unlikely but are very large should the situation happen to occur. The downside is manageable, and, averaged over the population, there is a significant net benefit of lives and property saved. We buy smoke detectors for the overall benefit.[i]
The analogy is an apt one. It is true that screening mammography is not perfect. It will not detect all breast cancers, not all of those detected will be curable, and it is possible that some of those detected (and therefore treated) might not have been lethal had they remained undetected. None of these facts provide a sound argument against screening. Rather they encourage continued research directed at developing better tests, treatments, and someday a cure. Until then, mammography remains the best tool in our toolbox for the fight against breast cancer.
-Dr. Catherine A. Young is a member of the BCRC Medical Advisory Committee
If you have questions on breast cancer screenings, or for more information on BCRC’s free mammography resources, please contact Rachel Shaefer at 512-524-2650 or firstname.lastname@example.org.
[i] Yaffe MJ, Pritchard KI, Overdiagnosing overdiagnosis, The Oncologist 2014; 19(2): 103-106