Xaluritamig (STEAP1×CD3 T-cell engager) + abiraterone posts 58% PSA50 and 43% ORR in chemo‑naïve mCRPC

Xaluritamig (xalu) is a STEAP1×CD3 bispecific T-cell engager combined with abiraterone acetate + predniso(lo)ne in an open-label Phase 1 dose exploration/expansion study (NCT04221542) in taxane-naïve mCRPC with ≤2 prior ARPIs (no prior abiraterone permitted); 39 patients were treated, with an expansion cohort at 1.5 mg Q2W (n=20; 19 PSA-evaluable, 7 RECIST-evaluable). In the expansion cohort, confirmed PSA50/PSA90 were 58%/47% and RECIST ORR was 43%, with median PSA response duration 6.7 months (95% CI 3.8–NE) and median rPFS 10.5 months (95% CI 8.1–NE); by comparison, abiraterone + prednisone in pre-chemo mCRPC historically delivered median rPFS ~16.5 months vs ~8.3 months for prednisone alone (COU‑AA‑302), so this early rPFS signal does not yet exceed what you’d expect from potent ARPI therapy in an earlier-line population. Safety was immune-/on-target heavy: myalgia 92% (G≥3 41%), CRS 64% (G≥3 7.7%), anemia 46% (G≥3 12.8%), with 2 G4 events and no G5 treatment-related AEs; 4 DLTs occurred across dose levels, and the program moved forward with 1.5 mg Q2W (aligned to the monotherapy RP3D) and is now in randomized Phase 3 (XALience; NCT07213674).