Posts Tagged H. Gilbert Welch

Mammography and overdiagnosis, revisited

Reading mammograms
[Editor Note: This is a greatly expanded version of my initial thoughts on a study about mammography published in the New England Journal of Medicine last week on my not-so-super-secret other blog. It’s such an important topic that I thought SBM should see my discussion too, and I couldn’t just cut and paste it. You deserve original material.]

I knew it. I just knew it. I knew I couldn’t get through October, a.k.a. Breast Cancer Awareness Month, without a controversial mammography study to sink my teeth into. And I didn’t. I suppose I should just be used to this now. I’m referring to the latest opus from H. Gilbert Welch and colleagues that appeared in the New England Journal of Medicine last week, “Breast-Cancer Tumor Size, Overdiagnosis, and Mammography Screening Effectiveness.” Yes, it’s about overdiagnosis, something I’ve blogged about more times than I can remember now, but it’s actually a rather interesting take on the issue.

Before 2008 or so, I never gave that much thought to the utility of mammographic screening as a means of early detection of breast cancer and—more or less—accepted the paradigm that early detection was always a good thing. Don’t get me wrong. I knew that the story was more complicated than that, but not so much more complicated that I had any significant doubts about the overall paradigm. Then, in 2009, the United States Preventative Services Task Force (USPSTF) dropped a bombshell with its recommendation that mammographic screening beginning at age 50 rather than age 40 for women at average risk of breast cancer. Ever since then, there have been a number of studies that have led to a major rethinking of screening, in particular screening mammography and PSA testing for prostate cancer. It’s a rethinking that affects discussions even up to today, with advocates of screening arguing that critics of screening are killing patients and skeptics of screening terming it useless. Depending on the disease being screened for, the answer usually lies somewhere in between. Basically, screening is not the panacea that we had once hoped for, and the main reason is the phenomenon of overdiagnosis. Before I go on, though, remember that we are talking about screening asymptomatic populations. If a woman has symptoms or a palpable lump, none of this discussion applies. That woman should undergo mammography.

Posted in: Cancer, Public Health

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The uncertainty surrounding mammography continues

Screening mammography

Mammography is a topic that, as a breast surgeon, I can’t get away from. It’s a tool that those of us who treat breast cancer patients have used for over 30 years to detect breast cancer earlier in asymptomatic women and thus decrease their risk of dying of breast cancer through early intervention. We have always known, however, that mammography is an imperfect tool. Oddly enough, its imperfections come from two different directions. On the one hand, in women with dense breasts its sensitivity can be maddeningly low, leading it to miss breast cancers camouflaged by the surrounding dense breast tissue. On the other hand, it can be “too good” in that it can diagnose cancers at a very early stage.

Early detection isn’t always better

While intuitively such early detection would seem to be an unalloyed Good Thing, it isn’t always. Although screening for early cancers appears to improve survival, the phenomenon of lead time bias can mean that detecting a disease early only appears to improve survival even if earlier treatment has no impact whatsoever on the progression of the disease. Teasing out a true improvement in treatment outcomes from lead time bias is not trivial. Part of the reason why early detection might not always lead to improvements in outcome is because of a phenomenon called overdiagnosis. Basically, overdiagnosis is the diagnosis of disease (in this case breast cancer but it is also an issue for other cancers) that would, if left untreated, never endanger the health or life of a patient, either because it never progresses or because it progresses so slowly that the patient will die of something else (old age, even) before the disease ever becomes symptomatic. Estimates of overdiagnosis due to mammography have been reported to be as high as one in five or even one in three. (Remember, the patients in these studies are not patients with a lump or other symptoms, but women whose cancer was detected only through mammography!) Part of the evidence for overdiagnosis includes a 16-fold increase in incidence since 1975 of a breast cancer precursor known as ductal carcinoma in situ, which is almost certainly not due to biology but to the introduction of mass screening programs in the 1980s.

As a result of studies published over the last few years, the efficacy of screening mammography in decreasing breast cancer mortality has been called into question. For instance, in 2012 a study in the New England Journal of Medicine (NEJM) by Archie Bleyer and H. Gilbert Welch found that, while there had been a doubling in the number of cases of early stage breast cancer in the 30 years since mass mammographic screening programs had been instituted, this increase wasn’t associated with a comparable decrease in diagnoses of late stage cancers, as one would expect if early detection was taking early stage cancers out of the “cancer pool” by preventing their progression. That’s not to say that Bleyer and Welch didn’t find that late stage cancer diagnoses decreased, only that they didn’t decrease nearly as much as the diagnosis of early stage cancers increased, and they estimated the rate of overdiagnosis to be 31%. These results are in marked contrast to the promotion of mammography sometimes used by advocacy groups. Last year, the 25 year followup for the Canadian National Breast Screening Study (CNBSS) was published. The CNBSS is a large, randomized clinical trial started in the 1980s to examine the effect of mammographic screening on mortality. The conclusion thus far? That screening with mammography is not associated with a decrease in mortality from breast cancer. Naturally, there was pushback by radiology groups, but their arguments were, in general, not convincing. In any case, mammographic screening resulted in decreases in breast cancer mortality in randomized studies, but those studies were done decades ago, and treatments have improved markedly since, leaving open the question of whether it was the mammographic screening or better adjuvant treatments that caused the decrease in mortality from breast cancer that we have observed over the last 20 years.

Given that it’s been a while since I’ve looked at the topic (other than a dissection of well-meaning but misguided mandatory breast density reporting laws a month ago), I thought now would be a good time to look at some newer evidence in light of the publication of a new study that’s producing familiar headlines, such as “Mammograms may not reduce breast cancer deaths“.

Here we go again.

Posted in: Cancer, Public Health

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Dr. H. Gilbert Welch has written a new book Over-diagnosed: Making People Sick in the Pursuit of Health, with co-authors Lisa Schwartz and Steven Woloshin.  It identifies a serious problem, debunks medical misconceptions and contains words of wisdom.

We are healthier, but we are increasingly being told we are sick. We are labeled with diagnoses that may not mean anything to our health. People used to go to the doctor when they were sick, and diagnoses were based on symptoms. Today diagnoses are increasingly made on the basis of detected abnormalities in people who have no symptoms and might never have developed them. Overdiagnosis constitutes one of the biggest problems in modern medicine. Welch explains why and calls for a new paradigm to correct the problem. (more…)

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