Breast cancer screening and detection after the 2024 USPSTF recommendation for women aged 40–49.

11126 Background: In April 2024, the US Preventive Services Task Force (USPSTF) expanded its biennial screening mammography recommendations to include women aged 40–49, citing rising breast cancer incidence in this age group and persistent disparities in outcomes. How this expansion has influenced diagnosis and stage at diagnosis in real-world practice is not yet well characterized. Methods: Using a subset of de-identified electronic health record data from Truveta, we identified women aged 40–74 who underwent screening mammography between 2018 and 2025, had no prior breast cancer diagnosis and who had evidence of outpatient care 6-18 months before and 1-12 months after screening. For patients with multiple eligible screening mammograms, only the first was retained for analysis. Analyses were restricted to health systems with available cancer stage data. April 30, 2024, was used as the cut point (pre- vs. post-guideline). Outcomes included: (1) screening uptake by age group, (2) breast cancers diagnosed within 180 days of screening, (3) stage at diagnosis (early [AJCC 0–I] vs. later [II–IV]). Diagnosis and stage were derived from clinical notes and categorized as early- (AJCC stage 0–I) versus later-stage (II–IV). Logistic regression, adjusted for race, ethnicity, rural–urban residence, and family history, was used to evaluate differences by age group and guideline period. Results: Among 985,687 women aged 40-74 who received a screening mammogram, 880,685 (89.3%) occurred pre-guideline and 105,002 (10.7%) occurred post-guideline. Women aged 40–49 comprised a substantially larger share of screenings post-guideline (53,227/105,002, 50.7% vs. 262,330/880,685, 29.8% pre-guideline p<.001). The likelihood of a breast cancer diagnosis within 180 days did not differ between the pre- and post-guideline periods for women aged 40–49 (OR 1.03, 95% CI 0.79–1.34) or 50–74 (OR 0.87, 95% CI 0.75–1.01). Among women diagnosed within 180 days with cancer stage information available (n = 3,866), the likelihood of early- versus later-stage diagnosis did not differ between the pre- and post-guideline periods for women aged 40–49 (early-stage: 63.6% vs. 68.3%; OR 1.26, 95% CI 0.72–2.21) or 50–74 (OR 0.91, 95% CI 0.67–1.24). Conclusions: Following the April 2024 USPSTF guideline expansion, screening mammography uptake among women aged 40–49 increased substantially, however the likelihood of a breast cancer diagnosis within 180 days did not significantly differ between the pre- and post-guideline periods. Stage at diagnosis did not differ significantly in the short post-guideline period; longer follow-up is needed to assess whether earlier detection translates to stage-shift benefits over time. These findings provide early real-world evidence to inform the ongoing risk-benefit discussion surrounding breast cancer screening in younger women.