The study will be conducted in 4 parts:

• Part 1: Participants who take part in this portion of the study will get different doses of JNJ-69086420. This part of the study will allow us to find the maximum dose of the study drug that is safe to take.
• Part 2: Participants who take part in this portion of the study will continue to get different doses of JNJ-69086420, but these dose levels will be based on the findings from Part 1.
• Part 3: Participants who take part in this portion of the study will get a combination of both JNJ-69086420 and JNJ-78278343 to find out if taking both study drugs at the same time is safe and beneficial.
• Part 4: Only participants who have hormone sensitive prostate cancer (HSPC) will be able to take part in this portion of the study. We will test the best dose of JNJ-69086420 from Parts 1 and 2 to find out if it has a safe, beneficial effect for people with HSPC after they get standard body radiation therapy.

If you choose to join this study, the part of the study in which you participate will depend on when you join. The study team can let you know which part is open to participants before you make your decision. Both study drugs are given as intravenous (IV) infusions. The number of doses you get will depend on how you respond to the study drug(s).