Androgen receptor signaling inhibitor (ARSI)

The study will be conducted in 4 parts and will commence with dose escalation of VIR-5500 as a monotherapy (Part 1), followed by combination escalation (Part 3a), monotherapy dose expansion (Part 2) and combination dose expansion (Part 4a). * Part 1 (Monotherapy Dose Escalation): Single-agent VIR-5500 dose escalation * Part 2 (Monotherapy Dose Expansion): Single-agent VIR-5500 dose expansion * Part 3 (Combination Dose Escalation): VIR-5500 plus another therapeutic agent dose escalation Part 3a (Combination Dose Escalation): VIR-5500 in combination with an androgen receptor signaling inhibitor (ARSI) * Part 4 (Combination Dose Expansion): VIR-5500 plus another therapeutic agent dose expansion Part 4a (Combination Dose Expansion): VIR-5500 in combination with an androgen receptor signaling inhibitor (ARSI)

The purpose of this study is to find out if giving radiation therapy (RT) to areas of metastatic prostate cancer at the time a participant is diagnosed will help control disease better than the usual treatment. This treatment is called metastasis-directed radiotherapy (MDRT). The usual treatment for prostate cancer that has spread to other parts of the body is to give lifelong treatment with hormone therapy (also known as androgen deprivation therapy or ADT). Participants may also be given prostate RT even if the disease is metastatic. Participants will receive hormone therapy (the standard treatment for prostate cancer) for 12 months. The hormone therapy agents may be taken by mouth or given as an injection. Participants will also have prostate RT. Up to 50 participants will have surgery to remove the prostate instead of having prostate RT. A portion of the participants will be randomized to receive MDRT to areas where the cancer has spread. For participants who have surgery to remove their prostate, they will be asked to allow tissue samples collected during the surgery to be sent to an outside lab for research tests and extra blood samples drawn for research tests before starting the study, and at the time the cancer becomes worse if applicable. Participation in the study will last approximately 12 months, and will be followed by their doctor for up to five years per standard of care. The main goal is to compare the efficacy of the standard of care (standard systemic therapy + definitive prostate-directed local therapy) versus the standard of care with metastasis-directed radiotherapy (MDRT) for consolidation of metastatic disease.