Κυριακή, 6 Μαρτίου 2016

MAMMOGRAM DEBATE CONTINUES

The mammogram debate is like a long serve/volley tennis match between Boris Becker and Ivan Lendl. The latest serve is from the US Preventive Services Task Force (USPSTF),[1] which reaffirmed that women should start mammograms at age 50 years. The American College of Radiology[2]advises that women start mammograms at age 40 years. The American Cancer Society[3] diplomatically meets midway: They advise women start at age 45 years.

No Clear Winners

There are no aces in this debate. Surprisingly, the science is still not settled. Clinical studies give different estimates of the survival benefits of screening mammograms. For example, in the Swedish Two-County study,[4] screening mammograms reduced breast cancer deaths by 30%. However, a Canadian study[5] could show no benefit of mammograms. Proponents of mammography say that the quality of mammograms in the Canadian study was so flawed that the trial is invalid.
The estimates of overdiagnosis—cancers that never harm—range from nonexistent[6] to 30%.[7] A single assumption, the background rate of breast cancer, is fiercely debated; higher background rates yield lower rates of overdiagnosis. Unsurprisingly, advocates of mammograms use the higher numbers to argue that there is little overdiagnosis, and the skeptics use the lower numbers to show the harms of screening.
As the scrutiny over mammograms increases, so do the arguments. Some authors ask for a higher burden of proof of benefits from screening, saying that screening mammograms have never been shown to reduce all-cause mortality[8], only deaths from breast cancer. Supporters of mammograms say that this is splitting (statistical) hairs; reduced breast cancer deaths means that the women are living longer, and that if reduction of all-cause mortality were the benchmark for screening, few screening tests would be approved.
Who is correct? This depends on how much you want to believe in mammograms. There is no right answer.

More Research Is Not the Answer

To know the actual survival benefit and actual overdiagnosis of screening mammograms, we need another large study comparing the death rates, from all causes, in women who have been screened with those who have not been screened. Such a trial is dead on arrival. Because we know that some women can benefit from screening, the study may not even be approved by hospital ethics committees.
Even if the trial is approved, it will be hard to recruit women for it, because so many are afraid of developing breast cancer. The participants must be followed for at least 35 years to show that screening actually makes women live longer. In that time, medical imaging will improve, and the results of the trial will be invalid. The debate would restart, leading to empiricism ad infinitum.
The debate between proponents and skeptics of mammograms has reached an impasse because neither side is willing to acknowledge two truisms: Mammograms save lives, and mammograms overdiagnose cancer. Science cannot break the impasse. But science is a red herring, because the debate is not about science. Science is fighting our battles because we do not want to answer the tough economic and political questions.

Time to Face Tough Questions

How hard should we try to prevent one death from breast cancer? Make no mistake, annual mammography between 40 and 45 years—the ages excluded by the guidelines from the American Cancer Society—will save some lives. How many women must be screened, how many must endure false-positive mammograms and negative biopsies, and how many must be harmed by overtreatment to save one life from breast cancer? Proponents and skeptics of mammograms should be upfront and state these numbers. If there is no upper limit to the number needed to screen to save one life, then why start mammograms at age 40, not 38?
I often argue against the optimism of screening with my colleagues. We end on conciliatory notes, such as "We need better data," "We need better ways of identifying more aggressive cancers," or "We need precision medicine." No doubt we need better information—but until we get better information, we must still decide what to do with the information we have.
Screening is a trade-off between costs and benefits. Science can tell you what these trade-offs are, but science can't tell you how the trade-offs should be valued. In Britain's National Health Service (NHS), where I trained as a doctor, women starting at age 50 have mammograms every 3 years, not every year. Values are different in the NHS because the opportunity costs are real. Chasing false-positive mammograms means less money to treat other diseases, such as hepatitis C. The budget-constrained NHS makes tough choices.
In the United States, talking about costs to save a life is taboo, but the costs are not trivial. One estimate[9] is that false-positive mammograms cost $4 billion a year. Costs do not disappear just because we do not like to talk about them.
It is easier to believe that screening has no benefit than to acknowledge the benefit and have the courage to say the benefit is too small and not worth the opportunity cost. It is easier to believe that screening has no harms than to acknowledge the harms and have the honesty to say that the harms are worth the benefits.
Many conflate wasteful care with expensive care and believe that reducing waste will reduce healthcare costs. This is a fallacy, because expensive care is not necessarily wasteful care. The more expensive technologies, such as 3-D mammograms and molecular breast imaging, will detect more breast cancers and save more lives, at greater costs. The screening debate is likely to get noisier.
Empiricism is the last refuge of politics. But we should not be fooled by the quest for perfect information—by that truism, "More research is needed." This is an excuse for dodging the real question. The real question is: How much should society spend to save one life? If there is no limit, there should be no opposition to mammograms, or any other technology, at any age.

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