Background: Medicare’s Oncology Care Model (OCM) was a voluntary, episode-based model between 2016 and 2021 that provided participating practices with additional payments to fund care enhancements such as extended clinical hours and urgent care. While it resulted in net losses for traditional Medicare beneficiaries, the OCM may have had “spillover” improvements on spending, utilization, and quality for commercially insured (CM) and Medicare Advantage (MA) members who were not targeted by the program. Methods: This retrospective analysis used claims from Elevance Health, a large national payer, to identify commercially insured and Medicare Advantage members diagnosed with breast, colorectal, lung, prostate, and pancreatic cancer initiating systemic therapy between 2014 to 2021. We identified 85 OCM practices and 581 matched non-OCM practices based on episode, practice, demographic, and market factors. The exposure variable was participation in the OCM model. All outcomes were defined in 6-month episodes; the primary outcome was overall inflation-adjusted spending; secondary outcomes included hospitalization and emergency room visits, and end-of-life acute care utilization. We utilized adjusted difference-in-differences linear probability models, with state-level fixed effects to control for market price variability, to estimate the association between OCM participation and all outcomes. Results: We studied 45,296 episodes of care in OCM practices and 122,231 episodes in non-OCM practices among CM and MA members during the post-implementation period. OCM participation was associated with a $5,275 (SE $749.40) reduction in total allowed spending (p<0.001), driven by reductions in outpatient and systemic therapy spending. OCM was associated with improvements in end-of-life utilization and ED visits but none in hospitalizations and timely chemotherapy initiation. Conclusions: Participation in the OCM was associated with modest spillover spending benefit onto CM and MA members, but minimal utilization and quality benefits. Resultant practice innovations may have benefited non-targeted patients. Evaluations limited to targeted patients may have underestimated the full impact of the OCM.

**p<0.05. ***p<0.01.