PROJECT SUMMARY/ABSTRACT Individuals dually enrolled in Medicare and Medicaid (“duals”) are a socially and clinically vulnerable population who account for a disproportionate amount of healthcare expenditures paid by both programs. Duals have a higher burden of disease compared to Medicare only beneficiaries, with more than 20% of individuals having multiple chronic conditions. Duals also have worse cancer outcomes. They are less likely to receive recommended screening, are less likely to receive definitive treatment after a cancer diagnosis, and have a higher risk of cancer-specific mortality. The complex social and healthcare needs of duals present a challenge in effectively delivering high quality cancer care to these patients. Accountable care organizations (ACOs) strive to provide coordinated, high-quality care to patients while containing costs for payers. As Medicare’s predominant ACO model, the Medicare Shared Savings Program (MSSP) has shown promise in improving quality of care, generating savings per beneficiary, and caring for clinically vulnerable patients. Whether the MSSP increases the quality of care across the cancer continuum for duals remains relatively unknown. The proposed study investigates how much the MSSP ACO model improves quality of cancer care for a clinically complex, vulnerable patient population. Studies will compare cancer outcomes for MSSP-attributed duals to duals who did not receive care from the MSSP ACO. Aim 1 will estimate the effect of MSSP ACOs on breast and colorectal cancer screening of duals using a quasi-experimental difference-in-difference analysis. Aim 2 will employ a time-to-event survival analysis to compare the time to treatment initiation after a breast or colorectal cancer diagnosis. Using generalized estimating equations, Aim 3 will assess differences in total Medicare spending in the first year of cancer treatment for duals with breast and colorectal cancer. Taken together, the results of this proposed study will inform policymakers and providers on whether value-based care reforms deliver better quality of care in screening and treatment of breast and colorectal cancer for dually enrolled beneficiaries.