Cancer Survivor or Victim of Overdiagnosis?

By H. GILBERT WELCH

Published: November 21, 2012

Hanover, N.H.

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FOR decades women have been told that one of the most important things they can do to protect their health is to have regular mammograms. But over the past few years, it’s become increasingly clear that these screenings are not all they’re cracked up to be. The latest piece of evidence appears in a study in Wednesday’s New England Journal of Medicine, conducted by the oncologist Archie Bleyer and me.

The study looks at the big picture, the effect of three decades of mammography screening in the United States. After correcting for underlying trends and the use of hormone replacement therapy, we found that the introduction of screening has been associated with about 1.5 million additional women receiving a diagnosis of early stage breast cancer.

That would be a good thing if it meant that 1.5 million fewer women had gotten a diagnosis of late-stage breast cancer. Then we could say that screening had advanced the time of diagnosis and provided the opportunity of reduced mortality for 1.5 million women.

But instead, we found that there were only around 0.1 million fewer women with a diagnosis of late-stage breast cancer. This discrepancy means there was a lot of overdiagnosis: more than a million women who were told they had early stage cancer — most of whom underwent surgery, chemotherapy or radiation — for a “cancer” that was never going to make them sick. Although it’s impossible to know which women these are, that’s some pretty serious harm.

But even more damaging is what these data suggest about the benefit of screening. If it does not advance the time of diagnosis of late-stage cancer, it won’t reduce mortality. In fact, we found no change in the number of women with life-threatening metastatic breast cancer.

The harm of overdiagnosis shouldn’t come as a surprise. Six years ago, a long-term follow-up of a randomized trial showed that about one-quarter of cancers detected by screening were overdiagnosed. And this study reflected mammograms as used in the 1980s. Newer digital mammograms detect a lot more abnormalities, and the estimates of overdiagnosis have risen commensurately: now somewhere between a third and half of screen-detected cancers.

The news on the benefits of screening isn’t any better. Some of the original trials from back in the ’80s suggested that mammography reduced breast cancer mortality by as much as 25 percent. This figure became the conventional wisdom. In the last two years, however, three investigations in Europe came to a radically different conclusion: mammography has either a limited impact on breast cancer mortality (reducing it by less than 10 percent) or none at all.

Feeling depressed? Don’t be. There’s good news here, too: breast cancer mortality has fallen substantially in the United States and Europe. But it’s not about screening. It’s about treatment. Our therapies for breast cancer are simply better than they were 30 years ago.

As treatment improves, the benefit of screening diminishes. Think about it: because we can treat most patients who develop pneumonia, there’s little benefit to trying to detect pneumonia early. That’s why we don’t screen for pneumonia.

So here is what we now know: the mortality benefit of mammography is much smaller, and the harm of overdiagnosis much larger, than has been previously recognized.

But to be honest, that general message has been around for more than a decade. Why isn’t it getting more traction?

The reason is that no other medical test has been as aggressively promoted as mammograms — efforts that have gone beyond persuasion to guilt and even coercion (“I can’t be your doctor if you don’t get one”). And proponents have used the most misleading screening statistic there is: survival rates. A recent Komen foundation campaign typifies the approach: “Early detection saves lives. The five-year survival rate for breast cancer when caught early is 98 percent. When it’s not? It decreases to 23 percent.”

Survival rates always go up with early diagnosis: people who get a diagnosis earlier in life will live longer with their diagnosis, even if it doesn’t change their time of death by one iota. And diagnosing cancer in people whose “cancer” was never destined to kill them will inflate survival rates — even if the number of deaths stays exactly the same. In short, tell everyone they have cancer, and survival will skyrocket.

Screening proponents have also encouraged the public to believe two things that are patently untrue. First, that every woman who has a cancer diagnosed by mammography has had her life saved (consider those “Mammograms save lives. I’m the proof” T-shirts for breast cancer survivors). The truth is, those survivors are much more likely to have been victims of overdiagnosis. Second, that a woman who died from breast cancer “could have been saved” had her cancer been detected early. The truth is, a few breast cancers are destined to kill no matter what we do.

What motivates proponents to use these tactics? Largely, it’s sincere faith in the virtue of early diagnosis, the belief that screening must be good for women. And 30 years ago, when we started down this road, they may have been right. In light of what we know now, it is wrong to continue down it. Let’s offer the proponents amnesty and move forward.

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. Screening could be targeted instead to those at the highest risk of dying from breast cancer — women with strong family histories or genetic predispositions to the disease. These are the women who are most likely to benefit and least likely to be overdiagnosed.

One final plea: Can we please stop using screening mammography as measure of how well our health care system is performing? That’s beginning to look like a cruel joke: cruel because it leads doctors to harass women into compliance; a joke because no one can argue this is either a public health imperative or a valid measure of the quality of care.

Breast cancer is arguably the most important cancer for a nonsmoking woman to care about. Diagnostic mammography — when a woman with a breast lump gets a mammogram to learn if it’s something to worry about — is an important tool. No one argues about this. Pre-emptive mammography screening, on the other hand, is, at best, is a very mixed bag — it most likely causes more health problems than it solves.

H. Gilbert Welch is 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.”