Adverse events will presented using National Cancer Institute Common Terminology Criteria for Adverse Events version 5 (NCI CTCAE v5).

All treated Participants in part 1

Adverse events will presented using National Cancer Institute Common Terminology Criteria for Adverse Events version 5 (NCI CTCAE v5).

All treated Participants in part 1

DLTs will be defined as:

Any treatment-related AEs for which a participant permanently discontinues a study treatment (other than daily prednisone) and that occurs during the first 2 cycles of treatment.

Any death not clearly due to the underlying disease or extraneous causes and that occurs during the first 2 cycles of treatment Greater than or equal to Grade 2 pneumonitis lasting greater than 5 days despite appropriate medical therapy and that occurs during the first 2 cycles of treatment Any neutropenic fever as well as Grade 4 neutropenia or thrombocytopenia for > 7 days that occurs during the first 2 cycles of treatment Any treatment-related AE that delays initiation of Cycle 2 or Cycle 3 of treatment by greater than 2 consecutive weeks.

All treated Participants in part 1

Adverse events will presented using National Cancer Institute Common Terminology Criteria for Adverse Events version 5 (NCI CTCAE v5).

All treated Participants in part 1

Number of participant deaths

All treated Participants in part 1

PSA-RR is the proportion of randomized participants with a 50% or greater decrease in PSA from baseline to any post-baseline PSA result. A second consecutive value obtained 3 or more weeks later is required to confirm the PSA response.

PSA Evaluable Population

Objective response rate per PCWG3 (ORR-PCWG3) is the proportion of participants who have a confirmed complete or partial best overall response (BOR) per PCWG3 among randomized participants who have measurable disease at baseline. The BOR is defined as the best response designation, as determined by the BICR, recorded between the date of randomization and the date of objectively documented radiographic progression, or last tumor measurement, whichever occurs first.

Study was terminated after safety lead in portion of part 1. Efficacy Data in part 2 was not collected, which includes this endpoint.

Time to response per PCWG3 (TTR-PCWG3) is the time from randomization date to the date of the first documented CR or PR per PCWG3, as determined by BICR.

Study was terminated after safety lead in portion of part 1. Efficacy Data in part 2 was not collected, which includes this endpoint.

Duration of response per PCWG3 (DOR-PCWG3) is the time between the date of first response (CR/PR per PCWG3) to the date of first documented radiographic progression per PCWG3 (as determined by BICR), or death due to any cause.

Study was terminated after safety lead in portion of part 1. Efficacy Data in part 2 was not collected, which includes this endpoint.

OS for all randomized participants is the time between randomization date and the date of death from any cause.

Study was terminated after safety lead in portion of part 1. Efficacy Data in part 2 was not collected, which includes this endpoint.