December 12, 2012

The Benefits and Harms of Routine Mammograms

The topic of routine screening mammography has become extremely controversial in recent years, especially following publication of a 2009 evidence review and subsequent U.S. Preventive Services Task Force recommendation that mammography be considered on an individual basis for women in their 40s, rather than automatically recommending mammograms for all women in that age group.

A new study published in the New England Journal of Medicine adds to the questioning of routine mammograms, concluding that “whatever the mortality benefit, breast-cancer screening involved a substantial harm of excess detection of additional early-stage cancers that was not matched by a reduction in late-stage cancers.”

The authors looked at data on how many women age 40 or older had screening mammograms and the incidence of early and late stage breast cancers. The assumption is that if widespread mammography is really helping to catch cancers at earlier, presumably more treatable stages, we’ll see fewer of those late stage breast cancers.

What they actually found was a large increase in detection of early cases (122 per 100,000 women), but a much smaller decrease (8 per 100,000 women) in late cases.

If mammograms were simply shifting diagnosis earlier, they should have seen about the same number for the increase in early cases and decrease in later cases. Instead, it resulted in diagnosis of numerous extra early cases that might not have progressed to more serious disease and would be considered over-diagnosis (with the corresponding over-treatment).

The researchers conclude that “the excess detection attributable to mammography in the United States involved more than 1.3 million women in the past 30 years.”

The authors did find that the death rate attributable to breast cancer had decreased over the last three decades, but they suggest that improvements in treatment over the last few decades may be primarily responsible.

As Dr. Diana Petiti, former vice chair of the USPSTF, explained in an email exchange:

Not all breast cancers detected by mammography would have caused a lump. Some breast cancers detected by mammography (we don’t know how many) revert to normal. Some breast cancers detected by mammography (we don’t know how many) don’t grow to the size of a lump. Some breast cancers detected by mammography (we don’t know how many) grow so slowly, they would not cause a lump in the forseeable lifespan of a woman.

Further not all lumps found by a woman (without mammography) would have caused death from breast cancer. Some breast cancers found as lumps (without mammography) are cured by treatment. Some breast cancers found as lumps (without mammography) grow so slowly that they never cause death due to breast cancer (which occurs because the cancer spreads). Some breast cancers found as lumps (with or without mammography) occur so late in life that something else causes death before the breast cancer spreads and causes death.

The newest data suggests that a not-small percentage of the breast cancers detected by mammography (without a lump) would not have killed the woman from breast cancer had it not been found.

While this is a complicated topic, this New York Times op-ed by Dr. H. Gilbert Welch, one of the authors of study published in NEJM, does a reasonable job of explaining it clearly. Welch, a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice and an author of “Overdiagnosed: Making People Sick in the Pursuit of Health,” includes this call for change:

What should be done? First and foremost, tell the truth: woman really do have a choice. While no one can dismiss the possibility that screening may help a tiny number of women, there’s no doubt that it leads many, many more to be treated for breast cancer unnecessarily. Women have to decide for themselves about the benefit and harms.

But health care providers can also do better. They can look less hard for tiny cancers and precancers and put more effort into differentiating between consequential and inconsequential cancers. We must redesign screening protocols to reduce overdiagnosis or stop population-wide screening completely.

Dr. David Newman, an emergency room physician in New York City and author of the book “Hippocrates Shadow: Secrets from the House of Medicine,” tackles the controversy head-on in a column titled ”Ignoring the Science on Mammograms“:

For years now, doctors like myself have known that screening mammography doesn’t save lives, or else saves so few that the harms far outweigh the benefits. Neither I nor my colleagues have a crystal ball, and we are not smarter than others who have looked at this issue. We simply read the results of the many mammography trials that have been conducted over the years. But the trial results were unpopular and did not fit with a broadly accepted ideology—early detection—which has, ironically, failed (ovarian, prostate cancer) as often as it has succeeded (cervical cancer, perhaps colon cancer).

More bluntly, the trial results threatened a mammogram economy, a marketplace sustained by invasive therapies to vanquish microscopic clumps of questionable threat, and by an endless parade of procedures and pictures to investigate the falsely positive results that more than half of women endure. And inexplicably, since the publication of these trial results challenging the value of screening mammograms, hundreds of millions of public dollars have been dedicated to ensuring mammogram access, and the test has become a war cry for cancer advocacy. Why? Because experience deludes: radiologists diagnose, surgeons cut, pathologists examine, oncologists treat, and women survive.

Newman also notes that mammography is not the only area of medicine ripe for questioning:

It is normally troubling to see an observational study posing questions asked and answered by higher science. But in this case the research may help society to emerge from a fog that has clouded not just the approach to data on screening mammography, but also the approach to health care in the United States. In a system drowning in costs, and at enormous expense, we have systematically ignored virtually identical data challenging the effectiveness of cardiac stents, robot surgeries, prostate cancer screening, back operations, countless prescription medicines, and more.

To further explore this topic, listen to this WBUR Boston (NPR) segment with Dr. Welch, Judy Norsigian, OBOS founder and executive director, and Dr. Otis Brawley, chief medical officer at the American Cancer Society. Norsigian also wrote a column for WBUR’s Cognoscenti section, “Do Screening Mammograms Do More Harm Than Good?

2 Responses to “The Benefits and Harms of Routine Mammograms”

  1. Alex Says:

    To read more about this, and fin dout what is going on with mammogram guidelines in Canada, read the Canadian Women’s Health Network’s article, Mammography screening: Weighing the pros and cons for women’s health

  2. Carl Says:

    Perhaps the most in-depth look into the controversies of mammography is Rolf Hefti’s (e)book “The Mammogram Myth: The Independent Investigation Of Mammography The Medical Profession Doesn’t Want You To Know About” revealing astonishing but not widely known facts about this popular screening procedure.

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