JNJ-78278343

The purpose of this study is to identify the recommended phase 2 combination dose (RP2CD) of JNJ-78278343 in combination with JNJ-95298177 in Part 1 (Dose confirmation) of the study and to determine how safe and tolerable the RP2CD is for treatment of participants with metastatic castration-resistant prostate cancer (mCRPC; a stage of prostate cancer where the cancer has spread beyond the prostate and is resistant to hormonal therapy) in Part 2 (Dose expansion) of study.

The purpose of Parts 1, 2A, and 2B of the study is to determine the recommended regimen for Phase 2 (RP2Rs) of combination of JNJ-87189401 with JNJ-78278343 and the purpose of Part 2C of this study is to determine how safe the RP2R(s) of the combination of JNJ-87189401 and JNJ-78278343 is, with or without apalutamide. Part 3 of this study evaluates the safety of the triplet combination of JNJ-87189401 and JNJ-78278343 with standard of care (SOC) lutetium Lu-177 vipivotide tetraxetan. Part 4 of this study further evaluates the safety of the triplet combination of JNJ-87189401 and JNJ-78278343 with JNJ-101556143 in participants with advanced prostate cancer.