275 Background: Medicare Part D was designed to reduce out of pocket (OOP) costs for Medicare beneficiaries, but the extent to which this occurred for patients with cancer has not been measured. The aim of this study is to quantify the impact of Part D eligibility on OOP cost for prescription drugs and utilization for cancer patients. Methods: Differences-in-differences analyses were used to estimate the effects of Medicare Part D eligibility on OOP drug costs, by comparing 4 year periods before and after Part D implementation. Analyses were based on data from the publicly available Medical Expenditure Panel Survey, a nationally representative, all-payer sample of the United States non-institutionalized civilian population. Our analysis compared per-capita OOP burden between Medicare beneficiaries (age 65+) with cancer to near-elderly individuals age 55-64 years old with cancer. Results: 2,077 near-elderly individuals with cancer and 4,723 individuals with Medicare and cancer were included (total n=6,800), representing over 85 million people. Prescription drug coverage increased among individuals with Medicare from before Part D (39%) to after (65%); in contrast, prescription drug coverage among the near-elderly remained stable before vs. after Part D (82.4% vs. 81.4%). The mean per-capita OOP cost for Medicare beneficiaries with cancer before Part D was $1,111 (SE ±45) and decreased to $694 (±35) after implementation of Medicare Part D—a decline of 37%. Compared with changes in OOP drug costs for non-elderly patients with cancer over the same period, implementation of Medicare Part D was associated with a further reduction of $286 per person. OOP costs for cancer-associated drugs (i.e., antineoplastic, pain medications, anti-emetics) accounted for 6.5-11.1% of the total OOP cost with no significant trends between 2002-2010. Conclusions: The implementation of Medicare D has significantly reduced OOP prescription drug costs for seniors with cancer, beyond trends observed for younger patients. Considering prescription drugs for all medical conditions, cancer associated drugs compose a minority of the cost, highlighting that cancer patients have many comorbid conditions contributing to overall costs.