Lead author Dejana Braithwaite, an assistant professor of epidemiology and biostatistics at the University of California, San Francisco, said from 1999 to 2006, data was collected on 2,993 older women with breast cancer and 137,949 women without breast cancer.
The study, published in the Journal of the National Cancer Institute, found no difference in rates of late-stage breast cancer between women screened annually and women screened biennially.
However, the study found 48 percent of women between the ages of 66 and 74 who were screened every year had false positive results -- a result indicating a given condition is present when it is not -- while 29 percent of women in the same age range who were screened every two years had false positives.
"Women ages 66-74 who choose to undergo screening mammography should be screened every two years," senior author Dr. Karla Kerlikowske, a professor of medicine at UCSF and a physician at the UCSF-affiliated San Francisco VA Medical Center, said in a statement.
"They get no added benefit from annual screening, and face almost twice the false positives and biopsy recommendations, which may cause anxiety and inconvenience."
Braithwaite concluded: "These results point to a need to consider life expectancy and co-existing illnesses in informing future recommendations about cancer screening in the elderly."