AAA817

This is a Phase II/III study. Patient population is adult participants with PSMA-positive mCRPC who had treatments with androgen receptor pathway inhibitor (ARPI) and taxane-based chemotherapy and progressed on or after \[177Lu\]Lu-PSMA targeted therapy. Treatment of interest: the investigational treatment is AAA817 regardless of subsequent anti-neoplastic treatment. The control treatment is investigator's choice of Standard of Care, regardless of subsequent anti-neoplastic treatment

The purpose of this study is to determine whether \[225Ac\]Ac-PSMA-617 (AAA817), given for up to 6 cycles at a dose of 10 Megabecquerel (MBq) +/- 10%, plus androgen receptor pathway inhibitor (ARPI), improves the radiographic progression free survival (rPFS) compared to investigator's choice of standard of care (SOC) (ARPI change or taxane-based chemotherapy or \[177Lu\]Lu-PSMA-617 (AAA617)) in adult participants with PSMA-positive metastatic castration resistant prostate cancer (mCRPC) treated with another ARPI as last treatment and who have not been exposed to a taxane-containing chemotherapy in the mCRPC setting nor have received any prior PSMA-targeting radioligand therapy.