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

One group will receive JNJ-78278343 (also called pasritamig), which is a medication that helps immune cells target cancer cells. The other group will receive placebo, which is an inactive substance that looks like the actual medication but contains no active treatment.

Neither you nor your doctor will know which treatment you are receiving. This is called a double-blind study design.

Both groups will also receive best supportive care, which includes standard treatments to manage symptoms and maintain quality of life.

You must continue your ongoing hormone therapy throughout the entire treatment period.

If you have had surgical removal of the testicles, no additional hormone therapy is needed.

If you have not had this surgery, you will continue receiving medications that suppress testosterone production. These are called GnRH analogs and may be either agonists or antagonists.

This hormone therapy must be maintained during all phases of the study treatment.

You will receive either JNJ-78278343 or placebo through an infusion into your vein.

The medication is prepared as a solution for infusion, which means it will be delivered directly into your bloodstream over a period of time.

The specific dosage, frequency of administration, and duration of each infusion session will be determined by the study protocol and communicated to you by the medical staff.

The treatment will continue according to the schedule established in the study design.

Throughout the study, you will undergo regular monitoring to assess how the treatment is affecting you and your condition.

Blood tests will be performed to check various health indicators, including blood cell counts, kidney function, and liver function.

Your PSA level (a protein produced by the prostate that can indicate cancer activity) will be measured regularly.

Your overall health status and ability to perform daily activities will be assessed using the ECOG performance status scale, which ranges from 0 (fully active) to 5.

Any side effects or changes in your health will be recorded and evaluated.

You will continue receiving the assigned study medication along with best supportive care.

The treatment will continue as long as it is considered beneficial and you do not experience unacceptable side effects.

Your medical team will monitor your response to treatment and overall survival, which is the main measure of how well the treatment works.

The study is expected to continue until May 2029, though your individual participation may be shorter or longer depending on your response to treatment and overall health.