Rationale: In pharmacokinetic studies, aprepitant was shown to be a moderate inhibitor of CYP3A4 activity. Etoposide is metabolised by CYP3A4.

Objective: to investigate the absence of a clinical relevant interaction between aprepitant and etoposide in TC patients treated with (B)EP.

Study design: A single centre, prospective, paired observational pharmacokinetic study in 12 patients with TC who are treated with etoposide during 5 days in combination with cisplatin with or without bleomycin conform the standard BEP or EP-protocol and who will be treated with aprepitant from day 3 until day 7 according to the routine antiemetic protocol. The effect of aprepitant on etoposide will be investigated within the same patient. In this study the patient will serve as its own control.

Inclusion Criteria:

• Patients with TC who will start or already started treatment with (B)EP
• Age of at least 18 years
• Patients from whom it is possible to collect blood samples
• Patients who are able and willing to give written informed consent prior to screening

Exclusion Criteria:

• Patients who are co-treated with drugs that could interfere with the metabolism of etoposide (including drugs classified as a weak, moderate or strong CYP3A4 inhibitor OR weak, moderate and strong inducers of CYP3A4 according to the table based on the Flockhart table (Appendix 1) less than 30 days prior to study or during the study.
• Creatininclearance <40 ml/min
• Severe liver dysfunction (bilirubin>ULN)

The study population will exist of patients treated at the Radboudumc who are diagnosed with TC and are treated with (B)EP according to standard treatment guidelines.