Study of AMG 509 in Participants With Metastatic Castration-Resistant Prostate Cancer

Parts 1, 2, 5 and 7: Participants with histologically or cytologically confirmed metastatic castration-resistant prostate cancer (mCRPC) who are refractory to a novel antiandrogen therapy (abiraterone acetate and/or enzalutamide, apalutamide, or darolutamide) and have failed at least 1 (but not more than 2) taxane regimens including for metastatic hormone-sensitive prostate cancer (mHSPC) (or who are deemed medically unsuitable to be treated with a taxane regimen or have actively refused treatment with a taxane regimen). Note: A taxane regimen is defined as a minimum exposure of 2 cycles of a taxane. Any NHT that has been administered and has been stopped for reasons other than progression will not be counted as an additional line of treatment.

Dose exploration phase: Novel antiandrogen therapy must have been given for treatment of metastatic disease.

Dose-expansion phase: participants must not have had more than 2 NHTs and 2 taxane regimens in any setting, and an additional up to 2 other systemic anti-cancer treatments are allowed (eg, anti-PD1, PARP inhibitors, radioligand therapies, sipuleucel-T, experimental agents) Note: Combinations are considered one systemic anti-cancer treatment.

Part 3: Participants with histologically or cytologically confirmed mCRPC who have received no or 1-2 prior NHTs (abiraterone acetate, enzalutamide, apalutamide, or darolutamide) given in any disease setting and who are deemed medically unsuitable to be treated with a taxane regimen or have actively refused treatment with a taxane regimen (unless taxane treatment was administered in HSPC setting). 0 1 prior PARP inhibitors or sipuleucel-T treatments are acceptable. Participants who received prior investigational therapy for the treatment of metastatic disease are not eligible.