Amgen’s investigational bispecific antibody, Xaluritamig (AMG 509), targeting STEAP1 and T-cell surface protein CD3, has been approved for a Phase 3 clinical trial in South Korea for metastatic castration-resistant prostate cancer (mCRPC).

According to South Korea’s Ministry of Food and Drug Safety (MFDS), IQVIA, a global contract research organization (CRO), received approval on December 4 to conduct the trial. This open-label, multi-center, randomized study will compare Xaluritamig with either cabazitaxel or second-line androgen receptor-targeted therapies, such as abiraterone (Zytiga) and enzalutamide (Xtandi), in mCRPC patients who have undergone prior chemotherapy.

Amgen secured U.S. FDA approval for the same Phase 3 trial on November 18. The global study plans to enroll 675 patients, including participants from South Korea, with primary endpoint evaluations expected by August 2028 and trial completion slated for November 2029.

In South Korea, the trial will involve several leading medical institutions, including Samsung Medical Center, Seoul National University Hospital, Bundang Seoul National University Hospital, the National Cancer Center, Chungnam National University Hospital, Severance Hospital, and Asan Medical Center.

The primary endpoint of the study is overall survival (OS), while secondary endpoints include radiographic progression-free survival (rPFS), objective response rate (ORR), duration of response (DOR), time to response (TTR), and treatment-emergent adverse events (TEAEs).

Xaluritamig, administered intravenously, is designed for advanced prostate cancer and other STEAP1-expressing solid tumors. Interim results from a Phase 1 dose-escalation study presented at the European Society for Medical Oncology (ESMO) Congress in September demonstrated promising outcomes. Among patients receiving high-dose formulations, 45.1% achieved a 90% reduction in prostate-specific antigen levels (PSA90), with a median OS of 17.7 months. Common treatment-related adverse events included cytokine release syndrome (72%), fatigue (45%), and myalgia (34%).

Prostate cancer is the third most common cancer among men in South Korea, following lung and stomach cancer, with 16,815 new cases reported in 2020. While localized prostate cancer has a high 5-year survival rate of 99%, survival drops sharply to 46% for cases with distant metastases. In 2021, 2,360 prostate cancer-related deaths were recorded in South Korea, many due to metastatic castration-resistant prostate cancer.

Despite advancements in treatment, there is no established standard therapy sequence for mCRPC. Current options include chemotherapy with docetaxel, androgen deprivation therapy, and agents such as cabazitaxel, abiraterone, and enzalutamide. Radiopharmaceuticals like Xofigo (radium-223 dichloride) and Pluvicto (lutetium-177 vipivotide tetraxetan) have been approved for bone-involved mCRPC.

Amgen’s Phase 3 trial for Xaluritamig offers a potential new avenue for addressing this challenging disease.