Yearly mammograms offer little benefit for women over 65. That's the conclusion of an eight-year study involving over 140,000 women over age 65.

Annual mammograms didn't catch any more late stage breast cancers than mammograms taken every two years, but they did give nearly twice as many false positives — apparent cancers that proved to be false alarms — leading to needless worry and unnecessary biopsies.

The researchers collected data from January 1999 through December 2006 for women aged 66-89 from a consortium of mammography registries in five states -- California, New Hampshire, North Carolina, Vermont and Washington. According to the study authors, this is the largest set of mammography data ever compiled in the Unites States. It included 2,993 women with breast cancer and 137,949 women without it.

With no difference in the rate of late stage cancers detected but a large increase in the number of false positives, there's no upside to older women getting screened annually.

Annual screeners aged 66-74 had a 48% chance of receiving at least one false positive result over 10 years, while 66-74 year old women screened every two years had only a 29% probability of a false positive over 10 years. Results were similar for women aged 75-89.

With no difference in the rate of late stage cancers detected but a large increase in the number of false positives, annual screening for older women offers no benefit, according to the study. Breast cancer in older women tends to grow more slowly than it does in younger women.

It's been over three years since the United States Preventive Services Task Force (USPTSF) recommended that women 40-49 no longer routinely have screening mammograms and that women 50-74 should have them every two years. Not everyone, however, agrees with these recommendations. The American Cancer Society doesn't. The ACS still recommends annual mammograms for all women age 40 and over, as long as they are in good health.

Recommendations and guidelines are rarely written in stone. Even the controversial USPTSF recommendations say that the decision whether a woman should have mammograms while in her 40s should be an individual one made in consultation with her doctor.

The current study suggests that most women 66 and older have nothing to gain by having mammograms more frequently than every two years and could be letting themselves in for needless grief by having them yearly.

An article on the study was published online in advance of publication in the Journal of the National Cancer Institute and will also appear in a future print edition of the journal.