HEME-25: Open-Label Feasibility Study of Elranatamab Utilized in Newly Diagnosed Plasmablastic Lymphoma With or Without HIV

Inclusion Criteria: * Age ≥ 18 years at time of consent * ECOG performance status (PS) 0 or 1 * Histologically and immunophenotypically confirmed PBL * Ann Arbor stage at initial diagnosis: stage I with lactate dehydrogenase (LDH) \> upper limit of normal (ULN) and/or bulky disease \>7.5 cm or stage II-IV * Received definitive front-line therapy for PBL with end-of-treatment PR or CR * Adequate bone marrow function with recovery from prior therapy, defined as: * ANC ≥ 500 cells/mcL * Platelet count ≥ 50,000 cells/mcL * Availability of archival tumor tissue (block or unstained slides) for mandatory central pathology review and correlative BCMA testing. Central pathology review and BCMA testing may be completed after enrollment. * Able to provide written informed consent and HIPAA authorization for release of personal health information, via an approved UIC Institutional Review Board (IRB) informed consent form and HIPAA authorization. If a subject is unable to consent, a LAR may provide consent on their behalf. * As determined at the discretion of the enrolling physician or protocol designee, the ability of the subject to understand and comply with study procedures for the entire length of the study * If capable of becoming pregnant: Negative serum or urine pregnancy test * If HIV-positive: * Receiving effective combined antiretroviral therapy * CD4+ T-cell count ≥ 50 cells/mcL within 4 weeks before enrollment Exclusion Criteria: Key inclusion criteria: * Age ≥ 18 years at time of consent * ECOG performance status (PS) 0 or 1 * Histologically and immunophenotypically confirmed PBL * Ann Arbor stage at initial diagnosis: stage I with lactate dehydrogenase (LDH) \> upper limit of normal (ULN) and/or bulky disease \>7.5 cm or stage II-IV * Received definitive front-line therapy for PBL with end-of-treatment PR or CR * Adequate bone marrow function with recovery from prior therapy, defined as: * ANC ≥ 500 cells/mcL * Platelet count ≥ 50,000 cells/mcL * Availability of archival tumor tissue (block or unstained slides) for mandatory central pathology review and correlative BCMA testing. Central pathology review and BCMA testing may be completed after enrollment. * Able to provide written informed consent and HIPAA authorization for release of personal health information, via an approved UIC Institutional Review Board (IRB) informed consent form and HIPAA authorization. If a subject is unable to consent, a LAR may provide consent on their behalf. * As determined at the discretion of the enrolling physician or protocol designee, the ability of the subject to understand and comply with study procedures for the entire length of the study * If capable of becoming pregnant: Negative serum or urine pregnancy test * If HIV-positive: * Receiving effective combined antiretroviral therapy * CD4+ T-cell count ≥ 50 cells/mcL within 4 weeks before enrollment Key exclusion criteria: * Prior BCMA bispecific therapy * Stable or progressive disease following front-line therapy as determined by the investigator * Receiving any other investigational agents * Expected survival \< 2 months * Known or suspected PBL involvement of the parenchymal brain or spinal cord at diagnosis. Asymptomatic leptomeningeal disease only will be allowed. * Uncontrolled intercurrent illness, including but not limited to uncontrolled infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements * Concurrent malignancy requiring active therapy within the last 3 years, except for the following: * Basal cell carcinoma limited to the skin * Squamous cell carcinoma limited to the skin * Carcinoma in situ of the cervix or breast * Adequately treated lentigo malignant melanoma * Localized prostate cancer * Active therapy consists of adjuvant or maintenance therapy to reduce the risk of recurrence of a malignancy that was previously treated with curative intent and with no evidence of active disease within 2 years prior to screening * Pregnant or nursing * PWH with a history of AIDS-defining opportunistic infection within the past year * Receipt of a live vaccine within 28 days prior to the first dose of study treatment