A review of medical claims from more than 1.5 million women aged 40 and older showed that only 50% had an annual mammogram in the years 2006 to 2009.
Among women aged 40 to 49, 47% had an annual mammogram. For women aged 50 to 64 and 65 and older, the figures were 54% and 45%, respectively.
Despite the outcry last year after a government task force said most women don't need annual breast X-rays, many women are skipping regular mammograms, says study leader Milayna Subar, MD, of Medco Health Solutions, which manages benefits for many insurers.
Breast screening rates are presumably lower among uninsured women, she says.
Garber tells WebMD that surveys in which women are asked to recall when they had their last mammogram show much higher breast screening rates than the new study.
But the new study is more accurate as it shows what women did, not what they recalled months or years later, she says.
Garber moderated a news briefing to discuss the findings at the San Antonio Breast Cancer Symposium. She is also president-elect of the American Association for Cancer Research, a sponsor of the meeting.
Regular Mammograms: Why Are Many Women Skipping Them?
Although the researchers didn't ask women why they don't get regular mammograms, Subar says conflicting guidelines are leaving women asking, "What should I do?"
The American Cancer Society and some other cancer groups have long recommended that women get annual mammograms starting at age 40. In November 2009, the U.S. Preventive Services Task Force, an independent panel of experts, said women in their 40s at average risk for cancer do not need mammograms and that women 50-74 need them only every two years.
No matter which guideline you follow, however, the numbers are dismally low, Subar says.
Among women 40 and older, only 60% had two or more mammograms over four years. Even in the 50 to 64 age group, the group that experts say most benefits from the screens, only 65% did.
Other possible reasons for the low breast screening rates are fears about discomfort from the test and lack of easily accessible screening centers in some areas, Subar says.
"Also, we're all so busy," she says.
Among women who do not have insurance, the cost of the screening can be a factor, she says.
Cost varies widely from state to state and facility to facility, according to the National Cancer Institute. Some state and local health programs provide mammograms free or at low cost to low-income, uninsured women.
Garber notes that insurers often send reminders when it's time for your next mammogram. Don't just delete the message; put it on your calendar right away, she advises.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.