A new study reinterpreting existing data increases the assumed benefits of breast cancer screening via yearly mammography.
Mammograms save lives – or do they?
The pendulum has swung wildly between two poles of that divisive issue for the past several years, ever since the 2009 release of new United States Preventive Services Task Force (USPSTF) recommendations around frequency and starting date of screening mammograms.
The recommendations – that women forgo having regular mammograms until age 50, and then have them only every other year – were a major revision to long-standing guidelines indicating that women who began having regular yearly mammograms at age 40 lowered their risk of dying from breast cancer. The new recommendations caused a firestorm of protest from many in the cancer community, including the American Cancer Society (ACS).
The USPTF’s findings didn’t materialize out of thin air, however; they were based on data showing that as many as 2,000 women needed to have mammograms in order to prevent just one woman from dying of breast cancer. Many of those 2,000 women experienced mammogram callbacks and over-diagnosis – defined as identification of a cancer that would never have been found (and wouldn’t have proven fatal) in a patient’s lifetime, without screening. Thus the USPTF concluded that the cost – emotional, physical, and financial – of yearly screening starting at age 40 was too high.
Now, a re-examination of the data of four large studies, including the USPSTF study itself, has determined that the benefit of mammography is much higher than previously thought.
Why the change in conclusion – was the data updated?
No – it was simply standardized, according to Dr. Robert A. Smith, senior director of cancer screening at the ACS. Speaking of the four studies, Smith said, “When we standardized all the estimates to a common scenario – i.e., the same exposure to screening, and a similar target population, period of screening, and duration of follow-up – the magnitude of difference between studies dropped from twentyfold to about fourfold.”
In other words, the original estimate of between 111 and 2,000 screenings needed to prevent one cancer death dropped to a range of 64 to 257 screenings to prevent one death.
“While there are genuine disagreements about over-diagnosis, methods which adjust for lead time and underlying incidence trends yield estimates which are modest and are outweighed by the mortality benefit,” concludes Smith.
So, is this the final word on subject – the benefits of early and yearly breast cancer screening outweigh the cost?
Probably not. “Torture the data until it speaks” is a phrase well-known to those familiar with data and statistics, and refers to the fact that any body of evidence can be re-examined in many ways to yield multiple (and differing) results.
There are some in the cancer and research community calling for women to at least be aware of the cost of regular mammograms: the possibility of over-diagnosis and unnecessary treatment, as well as the emotional and physical cost of mammogram callbacks and negative biopsies.
A December 30, 2013 editorial in the New York Times by Dartmouth professor H. Gilbert Welch, author of the book Overdiagnosed: Making People Sick in the Pursuit of Health, offers a well-reasoned approach to the subject.
Writes Welch, “There is no doubt that screening mammography in the United States leads to a lot of false alarms. Among a thousand 50-year-old American women screened annually for a decade, how many will have at least one false alarm? Our estimate ranges from 490 to 670… A screening program that falsely alarms about half the population is outrageous.”
Welch goes on to propose a series of clinical trials that would prove, once and for all, “what level of screening minimizes false alarms and over-diagnosis while saving the most lives.”
So at the end of the day, should you have a yearly mammogram starting at age 40 – or not?
There’s no right or wrong answer here; your goal is to understand the risks as well as the benefits, and then make the decision that’s best for you: physically, mentally, and emotionally.
Lawrence, L. (2013, December 12). Mammography benefits more consistent than previously understood. Retrieved from http://www.cancernetwork.com/sabcs-2013/mammography-benefits-more-consistent-previously-understood
Welch, H. G. (2013, December 30). Breast cancer screenings: What we still don’t know. Retrieved from http://www.nytimes.com/2013/12/30/opinion/breast-cancer-screenings-what-we-still-dont-know.html?_r=0
Published On: January 16, 2014