Science Debunks Mammography Myths
By Brett Parkinson, MD Intermountain Healthcare: Medically reviewed by Dr. C.H. Weaver M.D. Medical editor
At a time when unfounded claims have the potential to obscure the benefits of science, I find myself on a mission to debunk some damaging myths about mammography. That mission recently took me to the 2018 Society of Breast Imaging/American College of Radiology’s National Symposium where I delivered the opening remarks to kick off the symposium. Those myths are outlined here to help you make informed decisions about screening for you and your loved ones.
Much of the confusion concerning screening mammography guidelines are the result of a controversial recommendation in 2009 from the United States Preventive Services Task Force, or USPSTF. They said routine screening mammography shouldn’t begin until age 50 and should be provided every other year, rather than every year.
The evidence just doesn’t support this recommendation. We know from multiple randomized controlled clinical trials that regular screening saves lives, and that 40 percent of the years of life lost occur in women under age 50.
The incidence of breast cancer doubles between the ages of 35 and 40, and it increases further with every decade of life. Age 40 is the optimal time to start screening because approximately 20 percent of breast cancers occur in women under 50, most of whom are in their 40s. Since most major medical organizations no longer recommend self-examination, or even clinical breast examination by a doctor, those cancers will be missed without screening.
In the last 25 years, the death rate from breast cancer has decreased by about 35 percent. That’s largely due to the widespread availability of screening mammography. If you take into account the results of more recent studies, which include women who have actually been screened, instead of those just ‘invited’ to be screened, the decrease in death rate approaches 50 percent.
Is biennial screening as effective as annual screening? The answer is a flat NO.
The American Cancer Society’s position paper on mammography screening, which was published in JAMA in October 2015, says mortality increases by 20 percent when screenings occur every other year instead of every year. That’s an important number to remember.
Some claim that the “harm” of mammography screening outweighs the benefit, citing the effects of false positives and the potential for over-diagnosis. First, let me address the issue of false positives.
When a woman is called back from screening for additional tests, it’s not a false positive examination. Those examinations are interpreted as “incomplete,” not positive. A false positive is when a test says a woman has cancer and she doesn’t.
Some numerical context is important here. When a thousand women are screened, 100 will be called back for additional views and/or an ultrasound. Only 15 of those 1,000 women will undergo biopsy to identify five who have cancer. The rest will be told everything is okay. Look at it this way. To find one cancer from screening, we have to do three biopsies. That’s not a bad ratio.
When I started my practice in 1991, all women with suspicious mammographic abnormalities had to undergo surgery for diagnosis. The diagnosis is now made by needle biopsy with imaging guidance. The “harm” of an inconclusive exam has decreased significantly since women no longer undergo the risks associated with surgery and general anesthesia to get a conclusive diagnosis.
Others cite the anxiety of being called back for an abnormal screening as “harm”. Personally, I believe the notion that women can’t handle such anxiety is absurdly sexist. Studies have shown that an overwhelming majority of women would gladly endure a few days of anxiety — the time between the screening mammogram and the problem-solving diagnostic follow-up —to find breast cancer at an earlier stage. I’ve never heard anyone talking about men not being able to cope with the stress of false positive results from prostate screening.
Finally, there’s the misconception that 10 to 50 percent of breast cancers are over-diagnosed, meaning some tumors may not be lethal if left untreated. There is no documented case of an invasive breast cancer that has regressed without treatment.
The rationale behind the over-diagnosis myth is wrong – plain and simple. It was based on the faulty premise that the incidence of breast cancer has not changed – that we just diagnose more than would be expected. We have tumor registry data from as far back as 1940 that unequivocally disproves that.
Finally, there is the myth that women with dense breast tissue don’t benefit from mammography. It is true that screening is less sensitive in dense tissue, but it still picks up most breast cancers. And now that we have 3-D mammography, we can find even more cancers in women with dense and very dense tissue.
While there’s significant irony in the use of the word “myth” in a scientific talk, my radiology colleagues agree that uncertainty can negatively impact the number of women who get potentially life-saving mammograms. Here’s hoping the evidence helps you make well-informed, judicious decisions.
Dr. Parkinson is imaging director for Intermountain Healthcare and medical director of the Intermountain Medical Center Breast Care Center in Salt Lake City.