(RW) post-progression outcomes following first-line (1L) ribociclib (RIB) + aromatase inhibitor (AI) versus AI alone in African American and low socio-economic status (SES) patients with hormone receptor-positive/human epidermal growth factor recepto

1073 Background: RIB + endocrine therapy (ET) demonstrated significant overall survival over ET alone in all three phase III MONALEESA trials for HR+/HER2− MBC. RW studies can provide insight into pt subgroups who may be under-represented in clinical trials. This is particularly important for African American pts and those with low SES, groups who often face disparities in access and outcomes. This study assessed RW post-progression outcomes among these under-represented populations in the US, to guide treatment (tx) for those affected by social determinants of health. Methods: This retrospective study used deidentified data from the Flatiron Health Research Database, including 5,649 US women with HR+/HER2− MBC who began 1L RIB + AI or AI monotherapy between Jan 1, 2020 and Jan 31, 2025, with follow-up through Jul 31, 2025. Analyses of RW progression-free survival 2 (rwPFS2; time from start of 1L to first disease progression during 2L, or death during 1L or 2L, whichever occurred first) and RW chemotherapy-free survival (rwCFS) used unadjusted and adjusted time-to-event methods (Kaplan-Meier and Cox regression), with baseline differences addressed using inverse probability tx weighting with stabilized weights (sIPTW). Key pt demographics and characteristics were used for adjustment; details to be provided in the full presentation. Results: A total of 520 African American pts were included in the analysis; 243 received RIB + AI and 277 received AI monotherapy. After sIPTW, median rwPFS2 was 19.4 months longer for the RIB + AI group vs AI monotherapy (median 36.8 vs 17.4 months; HR, 0.44; 95% CI, 0.29–0.67). Median rwCFS was also extended by 14.3 months with RIB + AI (median 39.5 vs 25.2 months; HR, 0.49; 95% CI, 0.33–0.72). Among 1805 pts with low SES index (pts area-level SES categorized in the lowest two quintiles to represent the lowest 40% of block groups in terms of SES), 810 received RIB + AI and 995 received AI monotherapy. The median rwPFS2 was 14.2 months longer for those receiving RIB + AI vs AI monotherapy (median 37.2 vs 23.0 months; HR, 0.54; 95% CI, 0.44–0.67) after sIPTW adjustment. Similarly, median rwCFS was prolonged by 22.0 months for the RIB + AI group vs AI monotherapy (median 51.4 vs 29.4 months; HR, 0.58; 95% CI, 0.47–0.71). Conclusions: This study demonstrates that treating African American pts and individuals with low SES using 1L RIB + AI, compared with AI alone, leads to longer rwPFS2 and rwCFS. These results support 1L RIB + AI as an effective tx choice for these pt groups and underscores the importance of ensuring access to optimal tx for better outcomes.