This study is researching an experimental drug called odronextamab, referred to as study drug. The study is focused on patients with previously treated aggressive B-cell non-Hodgkin lymphoma whose cancer has stopped responding to treatment (also known as 'refractory') or has returned (also known as 'relapsed'). The aim of the study is to see how safe, tolerable and effective the study drug is when given alone.

The study is looking at several other research questions, including:

• What side effects may happen from taking the study drug versus Standard of Care (SOC)
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drug (which could make the study drug less effective or could lead to side effects)
• Comparing the impact from the study drug versus SOC on quality-of-life and ability to complete routine daily activities

Key Inclusion Criteria:

1. Histologically proven aggressive B-NHL, as described in the protocol. Availability of tumor tissue for submission to central laboratory is required for study enrollment. Archival tumor tissue for histological assessment prior to enrollment is allowed
2. Have primary refractory or relapse 12 months or less (≤) from initiation of frontline therapy Only patients who received 1 prior line of therapy containing an anti-Cluster of Differentiation 20 (CD20) antibody and anthracycline are allowed for enrollment
3. Have measurable disease with at least one nodal lesion with longer diameter (LDi) greater than 1.5 cm or at least one extranodal lesion with LDi greater than 1.0 cm, documented by diagnostic imaging (computed tomography [CT] or magnetic resonance imaging [MRI])
4. Intent to proceed to autologous stem cell transplant (ASCT), as described in the protocol
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1
6. Adequate hematologic and organ function.

Key Exclusion Criteria:

1. Primary central nervous system (CNS) lymphoma or known involvement by non-primary CNS NHL, as described in the protocol
2. History of or current relevant CNS pathology, as described in the protocol
3. A malignancy other than NHL unless the participant is adequately and definitively treated and is cancer free for at least 3 years, with the exception of localized prostate cancer, cervical carcinoma in situ, breast cancer in situ, or nonmelanoma skin cancer that was definitively treated
4. Any other significant active disease or medical condition that could interfere with the conduct of the study or put the participant at significant risk, as described in the protocol
5. Wash-out period from prior anti-lymphoma treatments and infections, as described in the protocol
6. Allergy/hypersensitivity to study drug, or excipients.

NOTE: Other protocol defined inclusion / exclusion criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf