Purpose Thenumberof targeted oral anticancer medications(TOAMs)has grown rapidly in the past decade. The high cost of TOAMs raises concerns about the financial aspect of treatment, especially for patients enrolled in Medicare Part D plans because of the coverage gap. Methods We identified patients with chronic myeloid leukemia (CML) who were new TOAM users from the SEER registry data linked with Medicare Part D data, from years 2007 to 2012. We followed these patients throughout the calendar year when they started taking the TOAMs and examined their out-of-pocket (OOP) payments and gross drug costs, taking into account their benefit phase, plan type, and cost share group. Results Wefound that 726 (81%) of the 898 patients withCMLwho received TOAMshad reached the catastrophic phase of their Medicare Part D benefit within the year of medication initiation, with a large majority of patients reaching this phase in less than a month. Patients without subsidies showed a clear pattern of a spike in OOP payments when they began treatment with TOAMs. The OOP payment for patients with subsidies was substantially lower. The monthly gross drug costs were similar between patients with and without subsidies. Conclusion Patients experience quick entry and exit from the coverage gap (also called the donut hole) as a result of the high price of TOAMs. Closing the donut hole will provide financial relief during the initial month(s) of treatment but will not completely eliminate the financial burden.