Background: Numerous oral anticancer drugs approved for metastatic prostate cancer are expensive and put patients at risk for financial toxicity. Mechanisms to mitigate these costs are complex to navigate and are variable for different patient populations. We examined the impact of high costs and insurance type on time on therapy and reason for discontinuation of oral medication in patients with prostate cancer. Methods: We identified patients with prostate cancer who filled prescriptions for abiraterone or enzalutamide at our comprehensive cancer center 1/1/17-3/31/19, or who were prescribed one of these therapies but could not fill due to cost. Those with commercial insurance or Medicare part D were included. Clinical and demographic data was extracted for evaluation. Primary outcome variables included initial out-of-pocket cost, time on treatment, and failure to fill medication due to cost. Analysis using chi squared, T-tests and ANOVA was performed to assess associations. Results: We identified 193 patients. Of these, 34% had commercial insurance and 66% had Medicare part D. Mean out-of-pocket expense for the first fill was $62 for patients with commercial insurance and $582 for patients with Medicare Part D. Among those who did not fill due to cost, 9 had Medicare Part D and 1 had commercial insurance. The mean time on therapy for those with commercial insurance was 452 days vs 442 days for those with Medicare Part D. At time of data analysis, 50% of those with commercial insurance vs 45% of those with Medicare Part D remained on treatment. Of those who discontinued, 50% of those with commercial insurance did so due to progression or death vs 44% with Medicare part D. 14% with commercial insurance and 15% with Medicare part D discontinued to due patient preference or toxicities. 1 patient with Medicare part D and no patients with commercial insurance discontinued due to cost. There was no difference in time on therapy by out-of-pocket expense (average 444 days for out-of-pocket < $100 vs 477 days for out-of pocket > $100; p = 0.6) although those with an initial out of pocket expense > $100 were more likely not to fill their medication (24% vs 1%, p < 0.01). Conclusions: Costs remain high for oral prostate cancer treatments. Our findings suggest disproportionate financial burden among patients with Medicare Part D causing a significant number of patients to forego recommended therapy. While high costs did lead to failure to fill, we did not observe significant differences in time on treatment for patients with Medicare part D or with high out-of-pocket expense. Additionally, there was not a significant difference in stated reason for stopping therapy. Further research on patient perceptions of financial assistance programs and medication costs are planned.