A multicenter phase I study of cabazitaxel, mitoxantrone, and prednisone for chemotherapy-naïve patients with metastatic castration-resistant prostate cancer: A department of defense prostate cancer clinical trials consortium study

Background: Cabazitaxel plus prednisone has significant activity in patients with chemotherapy-naïve and pretreated metastatic castration-resistant prostate cancer (mCRPC). Mitoxantrone has antitumor activity in mCRPC and nonoverlapping mechanism of action and toxicity profile.

Objective: To establish the maximally tolerated dose of the combination of cabazitaxel, mitoxantrone, and prednisone.

Methods and materials: Patients with chemotherapy-naïve mCRPC were prospectively enrolled in a multicenter phase 1 trial. Cabazitaxel 20 and 25mg/m² were each evaluated in combination with escalating doses of mitoxantrone (starting dose 4mg/m²), given with prednisone 5mg twice daily.

Results: A total of 25 patients were enrolled, with median age of 67 (range: 51-78) and prostate-specific antigen of 66.8ng/ml (range: 3-791.2). There were 4 dose-limiting toxicities (febrile neutropenia, n = 3; sepsis, n = 1). The maximally tolerated dose was cabazitaxel 20mg/m² plus mitoxantrone 12mg/m². The most common treatment-related grade≥3 related adverse events included neutropenia (n = 8; 32%), febrile neutropenia (n = 5; 20%), and thrombocytopenia (n = 4; 16%). The median number of treatment cycles was 8 (range: 2 to 19+). Decline in prostate-specific antigen to≥50% from baseline was observed in 15 patients (60%). Objective responses were observed in 10/14 (71%) evaluable patients. The median radiographic progression-free survival was 14.5 months (95% CI: 8.0-not reached (NR)), and median overall survival was 23.3 months (95% CI: 14.3-NR).

Conclusions: The approved single-agent doses of mitoxantrone and cabazitaxel were safely combined. The combination led to durable tumor responses in most patients. Further study of the combination is warranted.