Anahad O'Connor posted to nytimes.com/well:

In the year after an expert panel's recommendation that women delay regular breast cancer screenings until age 50, the number of women in their 40s undergoing mammograms slightly declined, a new study shows.

The study, carried out by the Mayo Clinic, found a drop of roughly 6 percent in the number of mammograms among these younger women, a change that the researchers called modest but still significant. While the panel had recommended that older women get a mammogram every other year rather than yearly up to age 74, the number of mammograms among women ages 50 to 64 remained fairly steady, the study also found.

The recommendations were made in late 2009 by the United States Preventive Services Task Force, a government-appointed group of outside medical experts. The recommendation that women in their 40s forgo routine mammograms stirred particular controversy.

The federal task force said that unless a woman has unusual risk factors for breast cancer, being screened so early could potentially lead to more harm than good because mammograms tend to spot cancers that grow slowly and might never prove lethal and could lead to unnecessary biopsies and other invasive tests and treatments.

In the new study, which was presented last week in Orlando at the annual research meeting of AcademyHealth, a research and policy group, Mayo Clinic researchers analyzed data from 100 health plans across the country, comparing the number of procedures that took place before the task force's guidelines with the number that were performed in the year that followed.

Over all, about eight million women ages 40 to 64 were included in the study.

In the year after the guidelines were published, nearly 54,000 fewer mammograms were performed on women ages 40 to 49. That represented a 5.72 percent decrease from the previous period. The authors said that the modest reductions probably reflected some public resistance to the new recommendations, in part because of conflicting guidelines from other groups, like the American Cancer Society, that urge more frequent routine screenings.