Phase 1b xaluritamig (AMG 509) STEAP1×CD3 bispecific T‑cell engager in mCRPC.

This Phase 1b, open-label study from Amgen evaluates the safety (primary) and early activity of xaluritamig at the proposed regimen in adults with metastatic castration-resistant prostate cancer who have progressed after an androgen receptor pathway inhibitor (ARPI) and previously received a taxane, while continuing androgen deprivation therapy (or after prior orchiectomy). Xaluritamig (AMG 509) is a STEAP1×CD3 bispecific monoclonal antibody (XmAb 2+1 format developed with Xencor) that binds STEAP1 on prostate cancer cells and CD3 on T cells to drive targeted T‑cell–mediated killing. The commercial/scientific angle is an “off‑the‑shelf” T‑cell engager approach in a setting where many patients have already exhausted hormonal therapy and chemo. Today’s care after ARPI + taxane typically includes options such as cabazitaxel, PARP inhibitors for HRR-altered disease, radioligand therapy (when eligible), and clinical trials; this study tests whether redirecting T cells to STEAP1 can add a new immunotherapy backbone in mCRPC.