Tirabrutinib is a second-generation BTK inhibitor with higher kinase specificity than that of the first-generation BTK inhibitor, ibrutinib.11 In the ONO-4059-02 phase 1/2 study, we evaluated safety, tolerability, efficacy, and pharmacokinetics of tirabrutinib in 44 Japanese patients with relapsed/refractory PCNSL who were administered oral tirabrutinib once daily (q.d.)at a dose of 320 or 480 mg, or of 480 mg under fasted condition. This evidence concerns the gene BTK and primary central nervous system lymphoma.