Thirty Years of Mammography

Why screen for breast cancer, or any other cancer for that matter? The objectives of any cancer screening program are to diagnose disease that is likely to cause death at a stage where early treatment confers some benefit. Hmmm.  At least two issues right here: how to determine the characteristics of disease that’s likely to cause death, and whether early treatment really does produce a survival benefit.  Weighty issues indeed, and the subject of hefty grants to study the same.  As Rick and I discuss this week on PodMed, at least one of these questions is addressed in a study in the New England Journal of Medicine, looking at thirty years of data on screening mammography.

Data from the National Health Interview Survey and SEER (Surveillance, Epidemiology and End Results) areas were crunched for this study.  The idea was that if mammography screening over these three decades was successful, the number of women presenting with late stage breast cancer at diagnosis should decline, with a corresponding increase in the diagnosis of early breast cancers.

The data clearly show an increased adoption of mammography screening among women 40 years of age and older in the 1980s and early 1990s.  Detection of early stage breast cancers increased over the study period from 112 cancers per 100,000 women to 234 per 100,000, so mammography was successful in the detection of early stage cancers.  However, over the same period the detection of late stage cancers only modestly declined, from 102 cases per 100,000 women to 94 per 100,000.  Yikes.  Not much change there, bringing both the authors of the paper and Rick and me to the conclusion that there’s an awful lot of overdiagnosis going on here.

Okay, you say, so what?  Isn’t finding an early breast cancer a good thing?  Well, now we have to examine the consequences of treatment, including mental anguish, biopsies, lumpectomies, genetic analyses, and no doubt for some women, bilateral mastectomy and use of drugs like tamoxifen.

The study did find that during this period of time, there was a reduction in the rate of death from breast cancer, from 71 to 51 deaths per 100,000 women.  Yet the bulk of these fell to a group of women who wouldn’t even be ordinarily screened using mammography: those younger than 40. This points to improvements in treatment as the primary factor in reducing deaths due to breast cancer.

What does this mean in terms of the utility of screening mammography?  As I quip in the podcast, I’ve never been a big fan of mammography anyway and would be happy to increase the interval between screenings.  Clearly it points to the need for a better screening tool as well as a better way to discern the dangerous cancers.  Just as is the case in prostate cancer management these days, many if not most men can safely watch and wait, with regular follow up, to see if their own disease crosses the threshold in becoming a cancer that needs treatment.  My own prediction is that like prostate cancer, as time goes on we will see more and more women dying with rather than of breast cancer.

Other topics this week include a study panning routine health check ups in BMJ, adolescents and how they try to build muscle in Pediatrics, and the best way to repair an aneurysm on the abdominal aorta, also in NEJM.  Until next week, y’all live well.

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