Zanubrutinib With Pemetrexed to Treat Relapsed/Refractory Primary and Secondary Central Nervous System (CNS) Lymphomas

Participants will receive 900 mg/m\^2 via IV infusion over 10 minutes every 3 weeks x 4-8 induction cycles (21 days per cycle) as part of the induction therapy.

"Participants will receive 320 mg PO daily or dose-adjusted when given concomitantly with CYP3A4 inhibitor on Days 3-19 of each induction cycle x 4-8 cycles (21 days per cycle) as part of the induction therapy.~For those on maintenance therapy, participants will receive 320 mg PO daily or dose-adjusted when given concomitantly with CYP3A4 inhibitor on Days 1-28 of each maintenance cycle (28 days per cycle) until the transplant (if applicable) or disease progression."

ASCT will occur in participants who are candidates for this procedure according to standard of care institutional protocols

WBRT will occur in participants who are candidates for this procedure but not candidates for ASCT according to standard of care institutional protocols