By Julie Steenhuysen

CHICAGO (Reuters) – Women 75 and older do not benefit from regular screening mammograms, researchers reported on Monday, offering some of the first evidence on whether screening makes sense in these women.

Although studies clearly show mammograms starting at age 50 prevent breast cancer deaths, until now, doctors have had little evidence about when to end screening, Dr. Otis Brawley of Johns Hopkins University and former chief medical officer of the American Cancer Society, wrote in editorial in the Annals of Internal Medicine.

“The study is important because a third of all American women die of breast cancer are diagnosed after the age of 70,” Brawley said in a telephone interview.

The U.S. Preventive Services Task Force, which sets screening guidelines, currently states that the evidence is insufficient to assess the harms and benefits in women 75 and older. Recommendations by other groups vary.

As a result, some 52% of women in the United States aged 75 and older still get regular mammogram screening, according to the paper published on Monday in the Annals of Internal Medicine.

“A lot of women over 75 and 80 are receiving mammograms,” study author Dr. Xabier Garcia-De-Albeniz of the Harvard School of Public Health, RTI Health Solutions and Massachusetts General Hospital, said in a telephone interview.

Brawley said clinical trials cannot be done to provide that evidence because too many people are convinced of the benefits of mammography, and would consider withholding screening to be unethical.

Garcia-De-Albeniz and colleagues set out to provide that evidence using claims data from the federal Medicare insurance program for the elderly. They studied data on more than 1 million women aged 70 to 84 who underwent mammograms from 2000 to 2008. Women in the study had a life expectancy of at least 10 years and no prior breast cancer diagnosis.

They found that in women aged 70 to 74, the benefit of screening outweighed the risks, which can include overdiagnosis, overtreatment and the anxiety of a potential breast cancer diagnosis. In women 75 to 84, screening did not substantially reduce the risk of dying from breast cancer.

The reason is likely that by 75, women are more likely to die from heart disease or neurological diseases such as dementia than breast cancer, the authors said.

Brawley said the findings underscore the need for more research to understand breast cancer in older women and better treatments for women in this age group.

(Reporting by Julie Steenhuysen; Editing by Marguerita Choy)