Breast cancer screening has significantly reduced breast cancer mortality in younger women. Its benefits for women over 70 years old or older are less clear, however.

Most randomized clinical trials (RCTs) of screening that have been done in women in their forties to early seventies have concluded that women should get screened for breast cancer regularly. Yale University researchers decided to look at whether continued screening benefited older women’s health enough that it should continue to be recommended after age 70.

In an older population, continued screening may lead to the over-diagnosis of breast cancer — the detection of cancer that is unlikely to cause symptoms during a patient’s lifetime. When the researchers estimated the risk of breast cancer over-diagnosis in a group of women 70 years old or older, they found screening was associated with an increased incidence of cancer diagnosis, a finding that suggests older women have an increased risk of over-diagnosis if they choose to continue getting screened, which may do more harm than good.

An estimated 31 percent of breast cancers were overdiagnosed among women ages 70 to 74 who continued screening.

One of the consequences of over-diagnosis of breast cancer is over-treatment, Ilana Richman, corresponding author on the study, told TheDoctor. Doctors can end up treating everyone, regardless of age, because all they know is that the patient has been diagnosed with breast cancer. Patients very often undergo surgery for breast cancer, and some will also have radiation and chemotherapy. They may also get endocrine therapy, depending on what kind of cancer they have. Most of these treatments can be particularly hard on the bodies of older women who may have other health conditions or limited mobility, Richman explained.

The serious psychological toll that receiving a cancer diagnosis can take is another consequence of over diagnosing older women. A cancer diagnosis changes the way a person thinks about themselves and their future. “Just receiving that diagnosis can be life changing. It’s a big deal,” said Richman, an assistant professor at the Yale University School of Medicine.

On the plus side, if cancer is detected early, screening can reduce older women's need for more aggressive treatments later, Richman explained. Some women have been screened throughout their lives and derive a feeling of security from being screened, and would rather know than not know. Other women, however, may be glad they don’t have to get screened any more, since they have been screened for many years and nothing has ever been wrong.

Data from almost 55,000 women 70 years old and older in the SEER (Surveillance, Epidemiology, and End Results)-Medicare registry were included in the current analysis. The women were divided into three groups: ages 70 to 74, 75 to 84 and 85 and older. All participants had a screening mammogram in 2002, and were followed for up to 15 years. Those who did not undergo another screening mammogram within three years of their 2002 mammogram served as the control group.

Among women ages 70 to 74 who continued screening, an estimated 31 percent of breast cancers were overdiagnosed; in women ages 75 to 84, about 47 percent were overdiagnosed; and among women 84 and older, about 54 percent of cancers were overdiagnosed.

The technologies used for mammography in this study were older technologies. Today, 3D mammography is used almost exclusively. While it is better at detecting breast cancers, it may actually contribute to overdiagnosis among older women. “Questions about how modern screening approaches may or may not contribute to overdiagnosis are important to think about,” Richman said.

The study and a related editorial are published in Annals of Internal Medicine.