We are doing this study to find the most effective, safe dose of an experimental drug called xaluritamig (the study drug). We want to know how well this drug works compared to the standard drugs for people who have metastatic castration-resistant prostate cancer.

Prostate Cancer

Adults who:

• Subject must have histological, pathological and/or cytological confirmation of

adenocarcinoma of the prostate

• mCRPC with ≥ 1 metastatic lesion that is present on baseline (CT), (MRI), or bone scan obtained within 28 days prior to enrollment
• Evidence of progressive disease
• Subjects must have prior orchiectomy and/or ongoing androgen-deprivation

therapy and a castrate level of serum testosterone

• Prior treatment with at least one ARDT
• Prior treatment with one taxane therapy
• No prior STEAP1-targeted therapy
• No anticancer therapy, immunotherapy, or investigational agent within 4 weeks

prior to first dose of study treatment

• No prior PSMA RLT within 2 months of first dose of study treatment received unless subjects received 2 cycles of therapy
• No history of allergic reactions or acute hypersensitivity reactions to the components

of the study therapies and their analogs.

• No active autoimmune disease that has required systemic treatment
• No history or evidence of inflammatory bowel disease (ulcerative colitis or Crohn

disease) or any other gastrointestinal disorder causing chronic nausea, vomiting,
or diarrhea

You will have a 2 in 3 chance of being placed in the investigational group given xaluritamig and a 1 in 3 chance of being placed in the control group, given the study doctor's choice of either cabazitaxel or second ARDT.
During eligibility testing (conditions for the study participation), you will discuss with your study doctor which study drug option you prefer to get if you are randomized (assigned by chance) to the control group: either cabazitaxel or second ARDT (enzalutamide or abiraterone acetate).
During the course of this study, you will visit the study site for around 24 visits if in the investigational group or 15 visits if in the control group (around 40 weeks for both groups). Across these visits, you will be examined by your study doctor, the study drug will be given by IV infusion (e.g. xaluritamig or cabazitaxel) or orally (abiraterone acetate or enzalutamide), depending on which study drug group you are allocated to, as well as having your blood tested.
During the study visits the following procedures may occur: physical exam, vital signs, ECG, echocardiogram, questionnaires, blood samples taken, imaging, (MRI/CT/bone scan/PET), and biopsy.
You will take part in the study for up to 56 months, including a minimum of 36 months of study drug and follow up. The ultimate time of study drug is varied, depending on how well you tolerate or respond to the study drug.