Paxalisib (GDC-0084) In Recurrent Or Refractory PCNSL

Inclusion Criteria: * Participants must be able to understand and willing to sign a written informed consent document. * Participant must have signed and dated an IRB/IEC approved written informed consent form in accordance with regulatory and institutional guidelines. This must be obtained before the performance of any protocol-related procedures that are not part of normal subject care. * Participant must be willing and able to comply with scheduled visits, treatment schedule, laboratory tests, and other requirements of the study. * Participants must be at least 18 years old on day of signing informed consent. * Participants must have a Karnofsky Performance Status (KPS) ≥ 70 * Participants must have histologically confirmed R/R primary DLBCL CNS lymphoma (from brain biopsy, CSF or vitreous biopsy). * Participants should have evidence of refractory or recurrent disease on MRI with measurable or evaluable enhancing disease. * Participants must have recovered to ≤ grade 1 or pre-treatment baseline from clinically significant toxic effects of prior therapy; exception, participants with ≤ grade 2 neuropathy may be eligible. * Participant with dexamethasone requirement of ≤ 8mg/day or bioequivalent with corticosteroid usage at a stable or decreasing dose 2 weeks prior to screening. * Participants must be able to undergo MRI. * Participants must demonstrate adequate as defined below (all screening labs should be performed within 14 days of treatment initiation): * Hematology …