A major new study has found that -- in older women -- mammograms done every two years were as effective as mammograms done annually and led to far fewer false positive results.
The study, published online Tuesday in the Journal of the National Cancer Institute, included more than 140,000 women ages 66 to 89 from across the country.
Frequency of mammograms among women in their 40s and 50s has been the subject of intense debate for more than two decades, but this older group of women has been much less studied.
A team led by researchers at UC San Francisco sought to answer the question: among older women, if a woman is screened for breast cancer every two years, instead of every year, will a deadly cancer be missed?
"We found that there really was no difference," Dejana Braithwaite, assistant professor of cancer epidemiology at UCSF and part of the research team, told me. "The women who were screened every two years were not at a greater risk. They did not have a higher probability of being diagnosed with late stage breast cancer compared to those women who were screened every year."
In addition, the women screened annually had a dramatically higher rate of false positives; they were called back for unnecessary mammograms or biopsies. In the study, nearly half of women screened annually -- 48 percent -- had a false positive over a 10-year period, versus about 29 percent of women screened every two years.
"The overall message is that the probability of false positive results is much greater with annual screening and yet there is no added benefit," Braithwaite said.
The U.S. Preventive Services Task Force created a firestorm of controversy in 2009 when it said women ages 50 to 74 should be screened every two years instead of annually. At that time, the task force said that "the current evidence is insufficient to assess the additional benefits and harms of screening mammography in women 75 years or older." Braithwaite says today's study is one step toward advancing the evidence.
"It doesn't mean to say that women in (their) 70s and even in their 80s should not be screened. Indeed, if they are in good health -- women in their 70s -- there is not reason for them not to be screened." But if they have other health issues, breast cancer screening could end up causing unnecessary harms.
"So there's a lot of uncertainty about the value of screening in these older age groups, and that's why we're trying to address is this gap of information in evidence," Braithwaite said.
And as the population ages, it's becoming an "increasingly important question," she concluded.
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