How Good is Mammography?

Over the past 40 years, many have come to view mammography screening as the “gold standard” for early breast cancer detection. But a number of recent studies have cast doubt on its benefits. Several studies have found links between mammography screening and overdiagnosis or overtreatment of breast cancer. Mammography is a valuable tool for detecting early cancers, but it can’t distinguish which cancers will progress and which won’t. It’s therefore possible for mammography to lead to harm for women in the form of mental distress, biopsies, surgeries, or chemotherapy and hormone treatments for disease that would never have caused symptoms.

The research, published recently in the British Medical Journal, is the latest salvo in a decades-long debate over the benefit of mammograms. The 25-year study of 89,835 women in Canada, aged 40 to 59, randomly assigned the volunteers to receive either annual mammograms plus physical breast exams or physical exams alone. The study “found no reduction in breast cancer mortality from mammography screening,” the scientists wrote, “neither in women aged 40-49 at study entry nor in women aged 50-59.” In addition to not reducing mortality from breast cancer, the study found, mammograms are leading to an epidemic of what the researchers call “over-diagnosis.” Nearly 22 percent of the invasive cancers detected by mammography were harmless, meaning they would not cause symptoms or death during a woman’s lifetime.

An accompanying editorial agrees that policy makers should stop pushing mammograms but points out that this is easier said than done.