Beginning in 2009, the U.S. Preventives Services Task Force (USPSTF) breast cancer screening guidelines recommended biennial mammography screening for women aged 50-74 years, and shared-decision making for women aged 40-49 years. We evaluated changes in screening interval after release of the 2009 recommendations. Methods: We compared screening intervals over the period between 2006 and 2012, expecting that the screening interval would lengthen over this time period, using data from the Breast

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... ancer Surveillance Consortium on 909,972 screening mammograms among 351,271 women aged 40-89 years. We stratified intervals based on whether the exam at the end of the interval occurred before or after the 2009 USPSTF decision. Differences in mean interval length by woman-level characteristics were compared using linear regression. Results: Contrary to expectations, the mean interval length (in months) minimally decreased after the 2009 USPSTF guideline compared to prior. Among women aged 40-49 years, the mean interval length decreased from 17.3 months to 17.1 months (difference À0.16, 95% confidence interval [CI] -0.30 to -0.01). Similar small reductions were seen for most age groups. The largest decreases in interval length in the post-USPSTF period were observed among women with a first-degree family history of breast cancer (difference À0.68, 95% CI, À0.82-À0.54) or a 5-year breast cancer risk ! 2.5% (difference À0.58, 95% CI, À0.73-À0.44). Conclusions: The 2009 USPSTF guideline update did not lengthen the average mammography screening interval among women routinely participating in mammography screening. Future studies should evaluate whether breast cancer screening intervals lengthen towards biennial intervals following new national 2015 breast cancer screening recommendations, particularly among women under 50 years.