Screening Mammograms: Do They Cause More Harm Than Good?

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Everyone loves the idea of screening for disease, especially cancer, and especially the life-threatening kind; catch the cancer early before it spreads, treat it, and you’ve saved a life. But catching something early isn’t always a good thing. Doing so can lead to extensive biopsies, operations, and chemotherapy that may make no difference in the clinical outcome of the patient and which are fraught with complications and side effects.

Mammography, however, has largely been held exempt from this criticism. The US Preventive Services Task Force (USPSTF) recommends that women who are not at increased risk of breast cancer begin screening at age 50. There’s been a 28 percent decline in the death rate from breast cancer over the past several decades–so surely this reflects the success of our sustained agenda to have all women get regular screening mammograms, right?

Do Screening Mammograms Save Lives?

In an effort to determine whether there is actually a cause-and-effect relationship between screening mammography and a decline in breast cancer mortality, investigators analyzed the incidence over 30 years of early-stage breast cancer (localized disease) and late-stage breast cancer (disease that has spread or metastasized). In brief, here’s what they found (the full study was published in The New England Journal of Medicine):

  • During the period after 1976–before screening mammography became a standard practice–the number of cases of early-stage breast cancer that was detected more than doubled. The increase was from 122 to 234 cases, a total of 112 cases annually for every 100,000 women. This clearly reflects the ability of mammography to detect small, localized, clinically undetectable breast cancers.
  • Over the same time period, the number of cases of late-stage breast cancer declined from 102 to 94 cases, a decrease of only 8 cases.
  • Because we can safely assume that late-stage breast cancer develops from early-stage disease, this means that only 8 of the additional 122 cases of early-stage breast cancer would have progressed to late stage disease; the other 114 women–122 minus 8–per 100,000 women per year were thus overdiagnosed–that is, early detection afforded them no benefit; their cancers would never have led to clinically significant disease. Taking a broader look, this means that over 1 million women over the 30-year period were given a diagnosis of breast cancer that offered them no clinical benefit and subjected them to subsequent biopsies, operations, and chemotherapy with all the attendant emotional and physical side effects!

The results of this study suggest that, as one of the authors later wrote, “These screenings are not all they’re cracked up to be.” In other words, the decline in breast cancer mortality doesn’t appear to arise from early detection, but rather from improved treatment.

Screening Mammography vs. Diagnostic Mammography

So what do we do with this information? First, understand that screening mammography is different from diagnostic mammography, which is used for patients with a detectable lump in her breast. Mammography still plays an important role in this scenario. Similarly, there are good reasons to continue to advocate for screening mammography in women who are at high risk, such as those who are genetically predisposed to breast cancer. But for everyone else, the question is very much on the table.

Understand the Risks and Benefits

Talk over the risks and benefits of screening mammography with your health care provider. Think about how you would respond to a mammogram report of early-stage breast cancer and what you might or might not choose to do about it. Here at One Medical, we will continue to report on this very important issue, and do the best we can, even with limited data, to help you make the decision that is right for you.

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The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, the San Francisco Bay Area, Seattle, and Washington, DC.

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