This study is for men with metastatic castration-sensitive prostate cancer (mCSPC). Metastatic means the cancer has spread to other parts of the body. Castration-sensitive means the cancer is affected by hormones like testosterone. Saruparib (AZD5305) is a new drug being tested against a placebo (a fake treatment) to see if it works better when used with other hormone treatments (new hormonal agents or NHA). About 1800 men will join the study and be randomly split into two groups. One group will get Saruparib with NHA, and the other group will get a placebo with NHA. They will continue treatment until the cancer progresses or they stop for another reason. Doctors will use scans to check on the cancer's progress. The study will look at how long the cancer stays controlled without getting worse.

Key Points:

• The study includes regular scans and treatment until disease progression or other reasons to stop.
• Participants must be free of certain health issues and agree to not father children during the study.
• Safety and effectiveness will be monitored by an independent committee.