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SAN FRANCISCO -- Rates of screening mammography among women younger than 50 declined within 2 months of a negative recommendation by the U.S. Preventive Services Task Force (USPSTF) and have remained below baseline rates, according to a study reported here.

The mammography rate among women 40 to 49 decreased by almost 8% in the period immediately after the 2009 release of the USPSTF recommendation against routine screening mammography for that age group.

Two years after publication of the screening guideline, the mammography rate among women 40 to 49 remained more than 5% lower than the baseline level.

In contrast, the screening mammography rate did not change among women 50 to 64.

In absolute terms, the decline in mammography rates meant that "more than 90,000 fewer mammograms were performed in women 40 to 49 in this dataset in the 2 years after the USPSTF update," Amy Wang, MD, of the Mayo Clinic in Rochester, Minn., and colleagues concluded in a poster presentation at the Breast Cancer Symposium.

"These findings underscore the need for further research on the benefits and risks of screening mammography, as it is difficult to act on numerous sources of contradictory information," they added.

In November 2009 the USPSTF issued updated recommendations for screening mammography. The recommendations included two key changes: The panel recommended against routine screening mammography for women younger than 50. Additionally, the USPSTF changed the recommended screening interval for women ≥50 to every 2 years instead of annually.

In recommending against routine mammography for younger women, the USPSTF, perhaps unknowingly, tossed a lighted match into a powder keg of controversy. In particular, opposition to the recommendation reached all the way to Congress, and Health and Human Services Secretary Kathleen Sebelius issued a statement distancing the Obama administration from the USPSTF decision.

The debate has continued to flare periodically almost 3 years after the USPSTF announced the decision.

Despite the widespread publicity and controversy, the recommendation's impact on clinical practice remained unclear. Wang and colleagues sought to inform on the issue by comparing rates of screening mammography before and after the USPSTF update.

Investigators analyzed claims data from more than 100 health plans for the years 2006 to 2011. They selected 2006 as the starting point to account for potential effects of the economic recession. They limited the analysis to women 40 to 64 because the dataset did not include Medicare recipients.

The analysis included 11.4 million women. Baseline mammography rates were 39.3 per 1,000 women in the 40 to 49 age group and 47 per 1,000 women in the 50 to 64 group.

Two months after the USPSTF announced the update, the screening mammography rate was 7.59% lower among women 40 to 49 as compared with rates prior to the announcement. The decline continued as the analysis extended to 2 years after the recommendation was published.

One year after the USPSTF update the mammography rate in younger women remained 5.33% below the baseline rate. At 2 years, 5.02% women ages 40 to 49 underwent screening mammography as compared with the baseline rate.

The screening rate among women 50 to 64 did not change at any point in the period included in the analysis.

Symposium invited discussant Thomas Buchholz, MD, said the study showed that the USPSTF recommendation impacted clinical practice related to screening mammography, but the reasons are not entirely clear.

"For some young women who really did not want to get their first mammogram, did it lead them not to get the mammogram? Perhaps, but we're not sure of that," said Buchholz, of the University of Texas MD Anderson Cancer Center in Houston. "I'm sure it influenced some doctors' recommendations, and that's a contributor. And I'm sure it influenced some third-party payers."

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