Upon entering the study, you will be randomly assigned to one of two treatment groups. This process is called randomization and ensures fair distribution of participants.

You will receive either xaluritamig plus abiraterone acetate or one of the investigator’s choice treatments, which may include docetaxel, cabazitaxel, or abiraterone acetate alone.

Before starting treatment, imaging scans will be performed. These may include computed tomography (a detailed x-ray scan), magnetic resonance imaging (a scan using magnets and radio waves), or a bone scan.

These scans must be completed within 28 days before enrollment to confirm the presence of cancer that has spread to other parts of the body.

If you are assigned to receive xaluritamig plus abiraterone acetate, you will receive both medications throughout the study period.

Xaluritamig will be given through a vein (intravenous infusion). The specific dosage, frequency, and duration will be determined by the study protocol.

Abiraterone acetate will be taken by mouth (oral administration). The specific dosage, frequency, and duration will be determined by the study protocol.

You will continue ongoing androgen-deprivation therapy, which is treatment that lowers male hormone levels, to maintain castrate levels of testosterone in your blood.

If you are assigned to receive one of the investigator’s choice treatments, you will receive one of the following options as determined by your doctor.

Option A: Docetaxel will be given through a vein (intravenous infusion). The specific dosage, frequency, and duration will be determined by the study protocol.

Option B: Cabazitaxel will be given through a vein (intravenous infusion). The specific dosage, frequency, and duration will be determined by the study protocol. This option is only available if you previously received no more than 6 cycles of docetaxel for earlier stage disease.

Option C: Abiraterone acetate will be taken by mouth (oral administration). The specific dosage, frequency, and duration will be determined by the study protocol.

You will continue ongoing androgen-deprivation therapy, which is treatment that lowers male hormone levels, to maintain castrate levels of testosterone in your blood.

In some cases, siltuximab may be administered. This medication is given through a vein (intravenous infusion).

The specific dosage, frequency, and duration will be determined by the study protocol if this medication is included in your treatment plan.

Throughout the study, you will attend regular visits for monitoring and assessments.

Blood samples will be collected to measure prostate-specific antigen levels (a protein produced by the prostate that can indicate disease status) and to check organ function.

Your testosterone levels will be monitored to ensure they remain at castrate levels (less than 50 nanograms per deciliter or less than 1.7 nanomoles per liter).

Physical examinations will be performed to assess your overall health and performance status (your ability to carry out daily activities).

Periodic imaging scans will be performed to evaluate how the cancer is responding to treatment.

These scans will assess whether the disease is stable, improving, or progressing according to standardized criteria called RECIST 1.1 (Response Evaluation Criteria in Solid Tumors).

Bone scans may also be performed to monitor disease in the bones.

Throughout the study, any side effects or adverse events you experience will be recorded and monitored.

You will be asked to report any new symptoms or changes in your health condition.

Serious adverse events will be carefully tracked and managed according to medical standards.

You will complete questionnaires at regular intervals to assess your quality of life and symptom burden.

These include the Brief Pain Inventory-Short Form to measure pain levels and how pain interferes with daily activities.

The Functional Assessment of Cancer Therapy-Prostate questionnaire will assess your physical, emotional, and functional well-being.

The EQ-5D-5L questionnaire will measure your overall health status and quality of life.

You will also complete questions about side effects you may be experiencing using a patient-reported outcomes tool.

Blood samples will be collected at specific times to measure drug levels in your bloodstream.

For xaluritamig, measurements will include maximum concentration, minimum concentration, and how the drug accumulates in your body over time.

For abiraterone, drug concentrations will be measured at the end of dosing intervals.

Additional blood samples will be collected to check for antibodies your body may develop against xaluritamig.

You will continue receiving your assigned treatment until the disease progresses, unacceptable side effects occur, or other discontinuation criteria are met.

The study will monitor the time until you require a subsequent therapy after stopping the study treatment.

The occurrence of symptomatic skeletal events (bone-related complications causing symptoms) will be tracked.

When you stop receiving study treatment, final assessments will be performed.

These will include physical examination, blood tests, and imaging scans to document your disease status.

Quality of life questionnaires will be completed to capture your final assessment while on study.

After completing treatment, you will enter a follow-up period where your health status will continue to be monitored.

Information about any subsequent cancer treatments you receive will be collected.

Long-term outcomes, including overall survival (how long you live after starting the study), will be tracked.

The study is expected to continue collecting data through August 2032.