KLK2-comPAS: This trial is recruiting people with metastatic castration-resistant prostate cancer (mCRPC) to evaluate whether immunotherapy combined with best supportive care is more effective than placebo combined with best supportive careA Phase 3 Randomized, Double-blind, Placebo-controlled Study of Pasritamig (JNJ-78278343), a T Cell Redirecting Agent Targeting Human Kallikrein 2, + Best Supportive Care Versus Best Supportive Care for Metastatic Castration-resistant Prostate Cancer

Inclusion

• Histologically confirmed adenocarcinoma of the prostate
• Metastatic castration-resistant prostate cancer (mCRPC): Disease that is metastatic either to bone, any lymph node, or both without clear evidence of metastasis to visceral organs at the time of screening
• PSA greater than or equal to (>=) 2 nanogram per milliliter (ng/mL) at screening
• In the opinion of the investigator, the next best treatment option is a clinical trial
• Participants should have had all life-prolonging therapies for which they are clinically eligible in the opinion of the investigator and to which they have access. Prior therapies could have been given in any disease setting (not limited to mCRPC). In particular, prior treatment specifications include receipt of the following:

Androgen-receptor pathway inhibitor (ARPI): Must have progressed on at least 1 ARPI and unlikely to benefit from retreatment with another ARPI

Taxanes: Should have received at least 2 previous taxane-based regimens. If a participant has received only 1 taxane regimen, the participant is eligible if:

1. Cabazitaxel is not available
2. The participant's physician deems the participant unsuitable to receive a second taxane regimen due to toxicity risk or prior intolerance Note: a taxane-based regimen consists of at least 2 cycles of a taxane (either as a single agent or in combination with other therapies) administered within the same 2-month period.

Radioligand therapy: Should have been previously treated with at least 1 dose of Prostate-specific membrane antigen (PSMA)-targeted lutetium radioligand therapy (eg, lutetium Lu-177 vipivotide tetraxetan), unless one of the following applies:

1. PSMA-targeted lutetium radioligand therapy is unavailable, not accessible, or not clinically indicated.
2. The participant's physician deems the participant unsuitable to receive PSMA-targeted lutetium radioligand therapy.

Polyadenosine diphosphate-ribose polymerase inhibitors (PARPi): Should have been previously treated with PARPi, if the participant has a known germline or somatic BRCA mutation and treatment is available

• Prior orchiectomy or medical castration (receiving ongoing ADT with a GnRH analog [agonist or antagonist]) prior to the first dose of study treatment and must continue this therapy throughout the treatment phase
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2
• Participants are eligible if they have the following values:

A) eGFR >= 30 milliliters per minute (mL/min) B) Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) less than or equal to (<=) 5 times the Upper Limit of Normal (ULN) C) Serum total bilirubin <= 3 * ULN D) Absolute neutrophil count (ANC) >= 1.0 *10^9/per liter (L) E) Hemoglobin >= 8.0 grams per deciliter (g/dL) F) Platelet count >= 75 * 109/L