This study will evaluate the efficacy and safety of the combination of inavolisib plus enzalutamide compared with physician's choice of alternative androgen receptor pathway inhibitor (ARPi) or docetaxel in biomarker-selected participants with metastatic castrate-resistant prostate cancer (mCRPC) who have received one prior second-generation ARPi.

Inclusion Criteria:

• Histologically or cytologically confirmed adenocarcinoma of the prostate without small-cell or neuroendocrine features
• Progressive metastatic CRPC, defined as any of the following: PSA progression, defined by a minimum of two rising PSA values from three consecutive assessments with an interval of at least 7 days between assessments and with a minimal starting value of PSA >=1 ng/mL; The most recent qualifying PSA value must be determined within 14 days of enrollment; Soft tissue disease progression, defined by Response Evaluation Criteria in Solid Tumors, Version 1.1 (RECIST v1.1); Bone disease progression, defined by PCWG3 criteria, with two or more new metastatic bone lesions on a whole-body radionuclide bone scan
• Treatment with at least one, but no more than one, prior second-generation ARPi (abiraterone, apalutamide, enzalutamide, darolutamide) for hormone- sensitive prostate cancer (HSPC) or CRPC
• Availability of a tumor tissue specimen that is suitable (e.g., adequate quality and quantity) for use in determining biomarker status
• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Fasting glucose <100 mg/dL and HbA1c < 5.7%

Exclusion Criteria:

• Presence of liver metastasis
• Prior treatment with any phosphatidylinositol-3-kinase (PI3K), protein kinase B (AKT), or mammalian target of rapamycin (mTOR) inhibitor, or with any agent with a mechanism of action of inhibiting the PI3K/AKT/mTOR pathway
• Type 1 or Type 2 diabetes mellitus
• Prior treatment for mCRPC with cytotoxic chemotherapy or novel hormonal treatments (e.g., androgen receptor degraders, CYP11 inhibitors), with the following treatments permitted: Prior docetaxel in mHSPC, providing no evidence of disease progression occurred during treatment or within 6 months of treatment completion; Prior docetaxel in the adjuvant or neoadjuvant setting providing no evidence of disease progression occurred during treatment or within 12 months of treatment completion; Prior treatment with sipuleucel-T, with the last dose administered >28 days prior to start of treatment; Prior PARPi therapy, as per local prescribing information, with the last dose administered >14 days prior to start of treatment; One prior RLT or radiotherapeutic agent (e.g., PSMA-targeted RLT, Radium 223) with the last dose administered >8 weeks prior to start of treatment
• Other concurrent anti-cancer therapy except for androgen deprivation therapy
• Treatment with strong CYP2C8 inhibitors, strong or moderate CYP2C8 inducers, or strong CYP3A4 inducers within 1 week or 5 drug-elimination half-lives, whichever is longer, prior to initiation of study treatment
• Transfusion of any blood product for the sole purpose of making a potential participant eligible for study inclusion or within 28 days of enrollment

For eligible studies, qualified researchers may request access to individual patient level clinical data. See Roche's commitment to transparency of clinical study information here: https://go.roche.com/data\_sharing