FALSE POSITIVE FEBRUARY 12, 2014
In late 2009, a government-appointed panel of medical experts came under withering attack for suggesting that Americans were getting too many mammograms—that early screening for breast cancer, starting at age 40, wasn't doing much good and might even be doing harm. The U.S. Preventative Services Task Force, as the panel is known, recommended that routine screenings wait until women reach 50, rather than 40—incurring the wrath of everybody from breast cancer surgeons, who were convinced the recommendation was wrong, to political conservatives, who thought it was a harbinger of the sort of rationing that health care reform would bring.
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, occsaionally, harmful. Aaron Carroll, the physician and blogger at The Incidental Economist, explains the findings:
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.
Does this settle the question of how frequently women should get mammograms? No—because “settling” the question is simply not possible.
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.”
One expert has already criticized the new study on similar grounds. And among those convinced regular, early mammograms still make sense is Richard C. Wender, chief of cancer control for the American Cancer Society. He told Gina Kolata of The New York Times that "combined data from clinical trials of mammography showed it reduces the death rate from breast cancer by at least 15 percent for women in their 40s and by at least 20 percent for older women."
But that's based on earlier studies with flaws of their own. Emanuel called the new study a “big deal”—in part because it comes at a time when everybody from policymakers to physicians to patients is becoming more aware that aggressive medical action can have drawbacks. “We are in this pendulum swing, when we are realizing these early interventions are not all that they were cracked up to be—and that’s probably true. …The other thing we’re learning is that there are lots of cancers that are indolent. It’s not just prostate cancer. There was a recent article showing that even in lung cancer we can see there are cancers that never develop into tumors that threaten people’s lives.”
One other thing to keep in mind, Emanuel notes, is that false positives lead to extra biopsies, which carry medical risks of their own. “This is a point I think nobody recognizes. Every time you go in for a biopsy and remove one of these nodules, you actually increase a woman’s chance of getting breast cancer—you’re stimulating an immune response, stimulating growth, as part of the healing process. You can have these incipient cancer cells that would have been knocked off by the immune system—you have them now growing. That’s increased risk.”
Mammography rates in the U.S. are among the highest in the world, thanks in part to effective lobbying from women’s groups, public health advocates, the medical establishment, and the manufacturers of screening devices. But in other countries, including some with similarly high screening rates, skepticism of mammography’s benefits have led experts to call for less testing—and, in one country, to eventually end universal screening altogether. As Kolata reports in the Times, "In a recent report, the Swiss Medical Board, an expert panel established by regional ministers of public health, advised that no new mammography programs be started in that country and that those in existence have a limited, though unspecified, duration. Ten of 26 Swiss cantons, or districts, have regular mammography screening programs."
Emanuel thinks the Swiss may be taking things too far. But this study, he says, reaffirms the growing consensus that the strong push to screen everybody regularly—not just high-risk patients, and not just at later ages—is misguided. “I don’t think advocating for it is unreasonable,” he says, “but there needs to be an asterisk there, a little subtlety. …Sometimes less medicine is better medicine for longevity.”