I’ve written plenty about our excess of prostate cancer screening, but I find the issue of mammograms even more fascinating (and I’ve written about a few times, too). Sadly, because unlike prostate cancer, which is rarely lethal, breast cancer sadly does strike down thousands of relatively young women in the prime of their lives every year. But, does increased mammogram screening actually do anything to prevent this? Best answer says no. Nice summary by Jon Cohn of a really important study new study:
On Wednesday, the British Medical Journal published one of the largest, most rigorous studies of mammography to date. If that study is right, the experts on USPSTF deserve some kind of apology.
The study followed almost 90,000 women (that’s a lot of people) over the course of 25 years (that’s a long time). And it was as close to a perfectly scientific study as you’ll find in this field. Researchers assigned women into two groups randomly. Women in one group got regular mammograms starting at 40. Women in the other group got only physical exams. Mammograms can pick up growths before it’s possible to feel them, so it was a good test of whether detecting those small growths translates to significantly more women surviving breast cancer…
The answer, according to the researchers, is a pretty definitive “no.” In fact, the researchers found, the primary consequence of such widespread screening was over-diagnosis, which led to procedures and treatments that were uncomfortable and costly and, occasionally, harmful.
Cohn than quotes from this Austin Carroll post on the topic:
Of the 44,925 women in the mammogram group, 500 died of breast cancer. Of the 44,910 in the no mammogram group, 505 died of breast cancer. This was not a significant difference. There wasn’t a significant difference if you looked at only older women (50-59) or younger women (40-49). There wasn’t a difference if you lengthened the screening period to seven years.
Mammograms did not affect mortality at all.
However, they did affect diagnosis. During the screening period, 666 cases of cancer were diagnosed in the mammography group versus 524 in the no mammography group. This meant an excess of 143 breast cancers were diagnosed with screening. Fifteen years later, the excess settled in at 106 cases of cancer.
More than 20% of the cancers detected by mammography were over-diagnosed. This means that mammography over-diagnosed one case of breast cancer for every 424 women screened with mammography. Do you know how many women we screen a year here?
This study is going to make a whole lot of people upset. It’s a large, well designed randomized control trial with a really long follow-up period. The people in the mammogram groups actually complied with screening in surprisingly high numbers. It’s hard to find fault with much of this. The data make a really good case that universal screening with mammograms does almost no good, and likely does harm. [emphasis mine]
Well, this should settle things– right? As if. Back to Cohn:
As Ezekiel Emanuel, the oncologist and former Obama Administration advisor, explained to the New Republic, studies like this are a “Rorschach test” for researchers. While people who tend to be skeptical of medical intervention will see evidence that we screen too much, people who tend err on the side of early, aggressive action will find flaws with the study. Among other things, they will point out, the study is based on screenings that took place 25 years ago—when the technology itself was less sophisticated.
“There will never be a truly definitive mammogram study,” says Emanuel, who was longtime head of the National Institutes of Health Bioethics Department and is now a vice provost at the University of Pennsylvania. “You’re in this circle where you will never resolve the issue. You need a long timeline to get the best results, but in that time span the technology always improves—and people will always say, well, this is based on old technology so it’s not so relevant anymore.”
This may be a Rorschach test but this study truly makes it hard to argue that there’s evidence for mammograms providing a net benefit. Unlike the studies that find in their favor, this was a randomized, controlled trial– the gold standard. Of course, doctors being doctors, I don’t actually expect anything to change any time soon, but I’m definitely not encouraging my wife to get a mammogram (though, of course that’s her call). That said, it’s also important to note that the non-mammogram group had annual breast exams. That’s important and should not be ignored. It’s just the the results suggest there’s no mammogram benefit above and beyond the breast exam.