The main objective of this study is to investigate the effect of small molecule inhibitors (SMIs), used in targeted therapy for tumours, on direct oral anticoagulants (DOACs).

Patients who receive anticoagulant therapy in the form of a direct oral anticoagulant (DOAC) and simultaneously receive anti-cancer targeted therapy with a small molecule inhibitor (SMI), potentially have an increased risk on thromboembolic complications and bleeding events due to interfering drug-drug interactions. Some SMIs influence CYP3A4 and/or p-glycoprotein (p-gp) for which DOACs are substrates. In this study, the effect of theoretically relevant SMIs on the pharmacokinetics, efficacy and safety of DOACs in patients with solid tumours will be investigated. For this purpose, plasma concentration analyses will be performed.

Inclusion Criteria:

• Diagnosed with a solid tumour
• 18 years of age or older
• Patients receive or start treatment with an SMI-DOAC combination, that may cause a clinically significant DDI at the level of CYP3A4 and/or P-gp, based on the SmPC
• Combined use of a DOAC-SMI combination is expected to be continued at the same dose for at least three weeks
• The DOAC is used for at least seven days and the SMI has already been used for at least 21 days at time of blood collection to ensure steady-state
• Patients receive a DOAC at maintenance dose

Exclusion Criteria:

• Unable to understand the information in the patient information letter
• Any concurrent medication beside the SMI and DOAC that is known to strongly inhibit or induce CYP3A4 or P-gp
• Patients who are pregnant or lactating

Patients with cancer who will be, or are already, treated with an SMI and a DOAC simultaneously, at the MUMC+ or Radboudumc can participate in this study.