RecruitingPhase 2Drug trialBoosting Osimertinib Blood Brain Barrier PenetrationThe goal of this proof-of-concept clinical study is to determine the effect of combining osimertinib with febuxostat on cerebrospinal fluid concentrations of osimertinib in patients with epidermal growth factor receptor (EGFR) mutated non-small cell lung cancer (NSCLC). The main question it aims to answer is: what is the effect of combining osimertinib with the ABCG2 inhibitor febuxostat on cerebrospinal fluid to unbound plasma osimertinib concentration ratio in patients with EGFR mutated NSCLC without central nervous system (CNS) metastases and without the ABCG2 34G\>A single nucleotide polymorphism (SNP)?