Background: In our prior phase III study (J ClinOnc 30:3998-4003, 2012) the addition of aprepitant to 5-day cisplatin regimens for germ cell tumors showed a significant improvement in complete response (CR) of 42%. Fosaprepitant has demonstrated non-inferiority compared to aprepitant in single day cisplatin chemotherapy and is approved as a single-dose alternative to the 3 day oral aprepitant regimen. This single arm phase II study is the first clinical trial evaluating fosaprepitant in patients receiving multi-day cisplatin. Methods: Germ cell tumor patients receiving 5 day cisplatin combination chemotherapy were eligible. Fosaprepitant 150 mg was given IV on days 3 and 5. A 5HT₃antagonist days 1-5 (days 1, 3, 5, if palonosetron) plus dexamethasone 20 mg days 1, 2, and 4 mg po bid days 6, 7, and 8 was administered. Rescue antiemetics were allowed at the discretion of the investigator. The primary objective was to determine the CR rate – no emetic episodes or use of rescue medications. Secondary objectives were to measure the incidence of vomiting or retching via patient log days 1-8, describe the use of rescue medications and the self-reported assessment of nausea days 1-8 using a 0-100 mm visual analog scale (VAS), as well as safety and toxicity. Results: 62 patients are enrolled, 57 are evaluable. All patients are male with a diagnosis of germ cell tumor receiving 5 day cisplatin-based chemotherapy. Median age 33 with age range of 15 to 66. 47 patients received BEP. 37 patients reported using rescue therapy, lorazepam most common. 15 patients reported emetic episodes, with 26 total episodes. There were 196 reported episodes of nausea > 5 on VAS in the 8 day reporting period. Only 16 of 57 (28.1%) reported a complete response. Conclusions: The preliminary data in this small phase II study, in contrast to our prior phase III study, appears to indicate a significantly lower CR rate with the substitution of fosaprepitant for aprepitant. Clinical trial information: NCT01736917