Over the last 25 years, mammography has become one of the most contentious issues in medicine. The National Cancer Institute lit a firestorm in 1993 when, after finding sparse evidence of benefits, it dropped its recommendation that women in their 40s get screened. Since then, most of the debate has remained focused on what age women should start getting mammograms, and the number of women mammograms help. Now, after more than 30 years of routine screenings, some experts are raising a different, perhaps less comfortable question: How many women have mammograms harmed?
If you include everything, the answer is: millions. Mammograms do help a small number of women avoid dying from breast cancer each year, and those lives count, but a 2012 study published in the New England Journal of Medicine calculated that over the last 30 years, mammograms have overdiagnosed 1.3 million women in the United States. Millions more women have experienced the anxiety and emotional turmoil of a second battery of tests to investigate what turned out to be a false alarm. Most of the 1.3 million women who were overdiagnosed received some kind of treatment—surgical procedures ranging from lumpectomies to double mastectomies, often with radiation and chemotherapy or hormonal therapy, too—for cancers never destined to bother them. And these treatments pose their own dangers. Though the risk is slight, especially if your life is on the line, a 2013 study found that receiving radiation treatments for breast cancer increases your risk of heart disease, and others have shown it boosts lung cancer risks too. Chemotherapy may damage the heart, and tamoxifen, while a potent treatment for those who need it, doubles the risk of endometrial cancer. In a 2013 paper published in the medical journal BMJ, breast surgeon Michael Baum estimated that for every breast cancer death thwarted by mammography, we can expect an additional one to three deaths from causes, like lung cancer and heart attacks, linked to treatments that women endured.