PROJECT SUMMARY Prostate cancer is the second leading cause of cancer death among men in the United States. It remains a challenging disease to treat given that many men do not benefit from immediate treatment, either due to slow-progressing disease or competing risks. This uncertainty about whether and when to treat has resulted in considerable variation in the management of prostate cancer, which we have shown to be driven by non-clinical factors such as financial incentives. Fee-for- service payment models provide incentives for utilization, but this may not always lead to benefits for patients, and in some instances can be harmful. Therefore, designing payment models that advance high-value healthcare by promoting both quality and reduced spending is critical. The Merit-Based Incentive Payment System (MIPS) in fee-for-service Medicare, introduced as part of the Medicare Access and CHIP Reauthorization Act, is a payment model that aims to improve the value of care by tracking quality measures and monitoring spending. Understanding how motivations to reduce spending implied by the MIPS policy affect quality and access to prostate cancer care is crucial. As Medicare annually escalates the weight of the spending component, spending is becoming increasingly important in determining success within the program. However, incentives to reduce spending may not always align with quality care. Additionally, incentives to reduce spending may have unintended consequences. For example, physicians may be influenced to avoid vulnerable populations, who are associated with the highest cost of care and worse cancer outcomes, in order to improve their performance within the program. In light of this, understanding the impact of the policy on quality of care and access for vulnerable populations is crucial. Using national Medicare claims data linked to physician quality reporting files, we will identify the impact of MIPS on quality and access to prostate cancer care utilizing methods adopted from econometrics. We will specifically assess the policy’s impact on access to care for Medicare’s most vulnerable population, dual eligible beneficiaries. The results of our study will enhance our understanding of how MIPS may influence care for men with prostate cancer and whether it promotes inequities in the delivery of care. The findings from this study will directly inform policymakers of potential gaps within the program so the policy may be improved in future iterations to enhance patient care.