A Phase II, Randomized, Open-Label, Multi-arm Study of TAS-115 for Castration-Resistant Prostate Cancer Patients With Bone Metastases

New treatments to improve quality of life and survival for castration-resistant prostate cancer patients with bone metastases are needed. We evaluated the safety and efficacy of the oral multikinase inhibitor TAS-115 in 50 patients. Overall, we observed improvements in bone metastasis and pain measures, and acceptable safety profiles with TAS-115. TAS-115 may be a useful treatment for these patients. Introduction: TAS-115 is an oral multikinase inhibitor targeting the MET proto-oncogene, vascular endothelial growth factor receptor, and colony-stimulating factor 1 receptor. We evaluated the efficacy and safety of TAS-115 in castration resistant prostate cancer (CRPC) patients with bone metastases. Patients and Methods: This phase II study, conducted in Japan, comprised 2 cohorts of CRPC patients. Cohort A included patients with bone metastasis and no history of docetaxel; TAS-115 200 to 400 mg/d was administered with abiraterone and prednisone. Cohort B included patients with symptomatic multiple bone metastases, post-or unfit for docetaxel, randomized 1:1 to receive TAS-115 400 or 600 mg/d orally, once daily, in a repeated weekly schedule of 5 days on/2 days off. The primary endpoint was bone scan index (BSI) response rate at Week 12 in each dose group. Results: Cohorts A and B included 24 and 26 patients, respectively. The 12-week BSI response rates for 200, 300, and 400 mg were 0%, 33.3%, and 16.7% in Cohort A, and for 400 and 600 mg were 7.1% and 25.0% in Cohort B. The best BSI response rates for 200, 300, and 400 mg were 0%, 66.7%, and 16.7% in Cohort A, and for 400 and 600 mg were 7.1% and 33.3% in Cohort B. A > 30% reduction in BPI-SF score was shown in 57.7% of patients in Cohort B. The most frequent Grade > 3 adverse drug reactions were hypophosphatemia (20.8%) in Cohort A and anemia (23.1%) in Cohort B. Conclusion: TAS-115 appears to demonstrate anti-tumor activity and acceptable tolerability in CRPC patients with bone metastases.