In November 2012, I found myself in a packed auditorium in Liverpool, England. Experts had gathered to discuss breast cancer screening guidelines in the UK. The audience was tuned in with rapt attention.
As someone who will need to make a choice about screening mammography at some point, this seemed like a no-brainer—yes I would like to be screened for cancer. What better way would there be to detect breast cancer?
But data from studies as well as opinions from experts and perpetuated in the media have been far from clear-cut. News reports with conflicting headlines—“Breast cancer screening saves lives–that’s no lie” and “Breast cancer screening causes more damage than previously thought”—were published on the same day in two major UK outlets. In fact, a debate over whether women should undergo routine breast cancer screening at all has been mounting in recent years.
To clarify the confusion and reach a consensus, experts convened at the 2012 National Cancer Research Institute Cancer Conference. The task force, composed of two statisticians, two oncologists and a patient advocate, had spent months combing through the available literature and listening to expert testimony in the hopes of creating a robust set of guidelines that patients and doctors could follow.
Although the panel acknowledged a rather high risk of overdiagnosis (just under 4,000 women are overdiagnosed each year in the UK), they ultimately concluded that breast cancer screening is crucial: screening mammography extends lives by detecting cancers early and allowing for earlier treatment. Specifically, the task force reported that women invited to screen had a 20% reduced risk of dying from breast cancer compared with those not screened, and that mammography prevented more than 1,300 deaths per year, or 43 deaths per 10,000 women invited to screen.
Still, after the meeting, some news outlets focused only on the negative conclusions, writing that the panel had determined that breast screening is “harming thousands.” These reports helped fuel greater confusion and undermine the nuances of the panel’s findings.
Similarly, in the US, the debate over breast screening—whether it saves lives or creates an overabundance of false positives—continues to rage on. In fact, even the recommendations for breast screening in the US conflict. The U.S. Preventive Services Task Force advises women to receive a mammogram every two years from age 50 while the American Cancer Society recommends a mammogram annually from age 40.
As Frederick Greene, MD, FACS, discussed in his June 2014 editorial in General Surgery News, now new concerns about the true extent of overdiagnosis have emerged from the Canadian National Breast Screening Study (BMJ 2014;348:g366), which concluded that most women should skip their routine mammogram because of overdiagnosis, and that, in women aged 40 to 59, screening mammography does not reduce deaths. But, as Dr. Greene pointed out, the study was deeply flawed and the conclusions should be viewed with skepticism.
Edward Hendrick, PhD, clinical professor of radiology at the University of Colorado-Denver, Anschutz School of Medicine, believes that the issue of overdiagnosis has been blown out of proportion.
“Deciding not to do screening mammography because of overdiagnosis is like deciding not to earn a salary because of taxes,” said Dr. Hendrick who estimates that the rate of overdiagnosis is actually between 1% and 11%.
A review of observational studies examining breast cancer overdiagnosis in Europe supports these figures. The review found that, when adjusting for breast cancer risk and lead time, overdiagnosis estimates were 2.8% in the Netherlands, 4.6% and 1.0% in Italy, 7.0% in Denmark and 10% and 3.3% in England and Wales (J Med Screen 2012;19:42-56). Additionally, evidence from a 29-year follow-up of the Swedish Two-County Trial found 31% fewer deaths in women ages 40 to 74 invited to screen biennially compared with those receiving usual care (P<0.0001) (Radiology 2011;260:658-663).
But given the conflicting reports and range of opinions, what are a patient and physician to do?
Clearly, gaining a better understanding of the disease—which women are at the greatest risk and which cancers are indolent or dangerous—would be an incredible step in the right direction. But until that time, screening choices may lie in the hands of each physician and each patient. The decision about the optimal age and frequency of screening should be a discussion where both parties evaluate the potential benefits and risks as best they can. In the absence of absolute evidence, that may be the most we can do for now.