ONO Pharmaceuticals Co., Ltd. announced it has completed target patient enrollment of the first arm (Part A) of the PROSPECT Study, a Phase 2 clinical trial evaluating the safety and efficacy of tirabrutinib (ONO-4059) in U.S. patients with relapsed or refractory primary central nervous system lymphoma (R/R PCNSL). The first arm (Part A) of the PROSPECT Study is evaluating the safety and efficacy of tirabrutinib in patients with R/R PCNSL who received previous treatment with high-dose methotrexate-based regimens. Enrollment is now complete for Part A. ONO PHARMA continues to enroll newly diagnosed and previously untreated PCNSL patients in the second arm of the study (Part B), evaluating tirabrutinib in combination with one of two high-dose methotrexate-based regimens as first-line therapy in the PROSPECT Study (theprospectstudy.com and clinicaltrials.gov).

PCNSL is a rare and aggressive extranodal non-Hodgkin lymphoma with historically poor survival rates. PCNSL affects the brain, its protective membranes, the spinal cord, and/or eye, without systemic involvement at the time of diagnosis. In the U.S., the incidence of PCNSL is approximately five out of 1,000,000 people per year, with higher rates in people over 65 years old.

Tirabrutinib is a highly selective irreversible Bruton's tyrosine kinase inhibitor discovered by ONO PHARMA in Japan. In March 2023, the U.S. Food and Drug Administration granted Orphan Drug Designation to tirabrutinib for the treatment of PCNSL. Tirabrutinib is currently approved for R/R PCNSL treatment in Japan, Taiwan, and South Korea.