The main objective of the study is to compare overall survival in participants receiving xaluritamig versus investigator's choice (cabazitaxel or second androgen receptor-directed therapy [ARDT]).

Inclusion Criteria:

• Participant has provided informed consent prior to initiation of any study-specific activities/procedures.

• Age ≥ 18 years (or ≥ legal age within the country if it is older than 18 years) at the time of signing the informed consent.

• Participant must have histological, pathological, and/or cytological confirmation of adenocarcinoma of the prostate. Mixed histologies (eg, adenocarcinoma with neuroendocrine component) are not permitted.

• mCRPC with ≥ 1 metastatic lesion that is present on baseline computed tomography (CT), magnetic resonance imaging (MRI), or bone scan imaging obtained within 28 days prior to enrollment.

• Evidence of progressive disease, defined as 1 or more PCWG3 criteria:

  • Serum PSA progression defined as 2 consecutive increases in PSA over a previous reference value measured at least 1 week prior. The minimal start value is 2.0 ng/mL.
  • Soft-tissue progression defined as an increase ≥ 20% in the sum of the diameter (SOD) (short axis for nodal lesions and long axis for non-nodal lesions) of all target lesions based on the smallest SOD since treatment started or the appearance of one or more new lesions or unequivocal progression of existing non-target lesions.
  • Progression of bone disease: defined by the appearance of at least 2 new bone lesion(s) by bone scan (as per the 2+2 PCWG3 criteria).

• Participants must have had a prior orchiectomy and/or ongoing androgen-deprivation therapy and a castrate level of serum testosterone (< 50 ng/dL or < 1.7 nmol/L).

• Prior progression on at least one ARDT (enzalutamide, abiraterone, apalutamide, darolutamide).

• Prior treatment with only one taxane therapy in the mCRPC setting. Note: Prior treatment with docetaxel in the metastatic hormone-sensitive prostate cancer (mHSPC) setting is permitted; however, participants must have also received one, and only one, taxane therapy in the mCRPC setting.

• Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1.

• Adequate organ function.

• Life expectancy of ≥ 12 weeks per the treating physician's assessment.

Key Exclusion Criteria:

Prior & Concomitant Therapy:

• Prior six transmembrane epithelial antigen of the prostate 1 (STEAP1)-targeted therapy.
• Any anticancer therapy, immunotherapy, or investigational agent within 4 weeks prior to the first dose of study treatment, not including androgen receptor pathway inhibitors (ARPIs) (abiraterone, enzalutamide, darolutamide, apalutamide): minimum washout of 2 weeks prior to the first dose of study treatment and androgen suppression therapy (eg, luteinizing hormone-releasing hormone/gonadotropin-releasing hormone [LHRH/GnRH] analogue [agonist/antagonist]).
• Prior Prostate-Specific Membrane Antigen (PSMA) radioligand therapy (RLT) within 3 months of the first dose of study treatment unless participants received < 2 cycles of therapy.
• Prior palliative radiotherapy within 2 weeks of first dose of study treatment. Participants must have recovered from all radiation-related toxicities.
• Concurrent cytotoxic chemotherapy, ARDT, immunotherapy, radioligand therapy, PARP inhibitor, biological therapy, investigational therapy. Note: Prior treatment with a PARP inhibitor is permitted as long as not within 4 weeks before first dose of study treatment.
• Prior radionuclide therapy (Radium-223) within 2 months of first dose of study treatment.
• Treatment with live and live-attenuated vaccines within 4 weeks before the first dose of study treatment.

Disease Related:

• Participants with a history of central nervous system (CNS) metastasis. Note: Participants with treated, asymptomatic, and clinically stable dural metastases are eligible.
• Unresolved toxicities from prior anti-tumor therapy not having resolved to CTCAE version 5.0 events grade above 1 or baseline, with the exception of alopecia or toxicities that are stable and well controlled AND there is an agreement to allow inclusion by both the investigator and the sponsor.

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.