Trends in biosimilar bevacizumab adoption and Medicare spending by socioeconomic deprivation and rurality, 2019-2023.

1529 Background: Biosimilar bevacizumab has the potential to reduce oncology drug spending, but the equity of its real-world adoption across socioeconomic and geographic contexts remains uncertain. Methods: We analyzed Medicare Part B provider-year claims from 2019-2023 for bevacizumab administrations. Biosimilar adoption was defined as the proportion of total bevacizumab services delivered as biosimilars. Neighborhood socioeconomic deprivation was measured using Area Deprivation Index (ADI) quintiles (Q1=least deprived; Q5=most deprived). Rurality was classified using provider-level Rural-Urban Commuting Area (RUCA) codes available in Medicare Part B, with urban defined as RUCA 1-3 and non-urban as RUCA ≥4. Adoption patterns were compared using chi-square tests for categorical outcomes and independent t-tests for spending measures. Temporal trends in adoption by ADI quintile were compared using logistic regression with Year × ADI interaction terms to test whether adoption trajectories diverged over time. Statistical significance was defined as p<0.05. Results: The study included 11,803 provider-year observations. Biosimilar market share increased from 0.5% of services in 2019 to 61.3% in 2023. In 2023, biosimilar adoption differed significantly by ADI quintile (p=0.0004), ranging from 55.7% in ADI Q4 to 81.3% in the most deprived quintile (Q5), patterns that may reflect institutional purchasing or practice-level factors rather than patient-level access alone. Adoption was higher in urban compared with non-urban areas (62.0% vs 33.6%, p=0.002), despite no baseline differences in 2019. Biosimilars were less expensive than originator bevacizumab in all years (all p<0.001). Mean per-administration savings increased from $8.03 (10.3%) in 2019 to $36.4 (52.2%) in 2023 (p=0.001). Originator prices did not differ by ADI in 2023 (p=0.58). Conclusions: Biosimilar bevacizumab adoption expanded rapidly and generated increasing Medicare savings, but uptake varied by socioeconomic deprivation and rurality. Differences in adoption, rather than pricing, appear to drive inequities in realized savings. Targeted policy strategies may be needed to promote equitable biosimilar diffusion in oncology care. Biosimilar bevacizumab adoption in 2023 by socioeconomic deprivation and rurality. Category Biosimilar share of services (%) ADI Q1 (least deprived) 58.1 ADI Q2 61.1 ADI Q3 61.7 ADI Q4 55.7 ADI Q5 (most deprived) 81.3 Urban 62.0 Non-urban 33.6