The generally accepted recommendation of regular breast-cancer screenings in older women just received a very heavy dose of skepticism.
A new study published in the British Medical Journal on Tuesday found that regular mammograms did not reduce the death rate from breast cancer. They did, however, lead to overdiagnosis and treatment.
The Canada-based study is a large-scale, long-term, in-depth look at the impact of screenings we take for granted as critical to cancer care. It randomly assigned 89,835 women, ages 40 to 59, to either a mammography group (annual screenings) or a control group (no mammography) over a five-year period. All women in the mammography group and those 50 to 59 in the control group received annual physical breast examinations as well; those 40 to 49 in the control received one physical examination followed by standard care.
The study found that of the 44,925 women in the mammography group, 666 invasive breast cancers were diagnosed during the five-year screening period. Of the 44,910 in the control group, 524 were diagnosed in this time. Of these, 180 in the mammography group and 171 in the control group died of breast cancer during the 25-year follow-up.
Over the course of the full study, 3,250 women in the mammography group were diagnosed with breast cancer and 500 died, compared with 3,133 diagnoses and 505 deaths in the control group. Age did not appear to have an impact.
The difference in death rate — 500 versus 505 — is not significant between the two groups, but the difference in diagnosis is. After 15 years of follow-up, the study found an excess of 106 breast-cancer diagnoses in the mammography group. Overall, 22 percent of breast cancers detected by screenings were overdiagnosed.
Mammograms have long been promoted as the necessary weapon to combat breast cancer, the second leading cause of cancer death in women. The American Cancer Society currently recommends annual mammograms for women age 40 and older. The National Cancer Institute recommends them every one to two years. The Susan G. Komen Foundation, the largest, most well-known breast-cancer organization in the U.S., includes regular screenings as a large part of its mission.
However, the new study complicates this assumption. Overdiagnosis can lead to unnecessary, harmful, and expensive treatment, and the tests themselves include small amounts of radiation that can be harmful in heavy doses.
While the findings do not necessarily change these recommendations, they raise questions about the universal screening prescription for what is clearly a pretty complex situation.