A Study of Niraparib in Combination With Abiraterone Acetate and Prednisone Versus Abiraterone Acetate and Prednisone for the Treatment of Participants With Deleterious Germline or Somatic Homologous Recombination Repair (HRR) Gene-Mutated Metastatic Castration-Sensitive Prostate Cancer (mCSPC)

To be part of this study, you must be a man with prostate cancer that has spread and has specific genetic changes called HRR gene mutations. Your cancer also needs to be responding to hormone therapy, meaning your hormone levels are low. The cancer spread must be visible on scans like CT, MRI, or bone scans. If you only have one spot on a bone scan, it needs to be confirmed by another type of scan like a CT or MRI.

You must have started hormone therapy at least 14 days before starting the study and be willing to continue it. You might have had some previous treatments, such as a maximum of six months of hormone therapy, up to 45 days of abiraterone acetate and prednisone, or up to two weeks of ketoconazole. Some limited radiation or surgery for symptom control is also allowed if it's not to all known cancer sites.

However, you cannot join if you've previously taken a similar drug called a PARP inhibitor. You also can't participate if you have certain adrenal gland problems or need to take corticosteroids (like prednisone) for a long time at high doses during the study. Short-term use of steroids or steroids used locally (like inhalers or creams) might be allowed.

If you join this study, it will involve several stages. First, there's a 'Prescreening Phase' where doctors will check your cancer cells for specific genetic changes to see if you're eligible. If you are, you'll enter the 'Screening Phase' for more checks to ensure the study is safe for you.

Next is the 'Treatment Phase,' where you'll receive either the new drug combination (niraparib with abiraterone acetate and prednisone) or the standard treatment (abiraterone acetate and prednisone) plus a dummy pill (placebo for niraparib). You won't know which group you're in. During this phase, you'll have regular appointments for imaging scans (like CT, MRI, and bone scans), blood tests (including PSA), and you'll be asked about your symptoms and how you're feeling. This helps doctors see how well the treatment is working and check for any side effects. This phase will last as long as the treatment is helping your cancer and you are tolerating it. After the treatment phase, there's a 'Follow-up Phase' where doctors will continue to monitor your health and cancer over time.