Utidelone for heavily pretreated metastatic castration-resistant prostate cancer after failing docetaxel treatment: An open-label, single-arm, phase II trial.

e17036 Background: The appropriate chemotherapy for metastatic castration-resistant prostate cancer (mCRPC) that progressed after docetaxel treatment remains unmet medical needs. Utidelone (UTD1) is a genetically engineered epothilone analog with antitumor activity in taxane-resistant cancers. UTD1 was approved for advanced breast cancer in 2021. This study was designed to evaluate the safety and efficacy of UTD1 in mCRPC. Methods: In this perspective, phase II clinical trial, men with progressive mCRPC after docetaxel and abiraterone, and/or enzalutamide, and/or apalutamide received UTD1 monotherapy treatment at a total dose of 150 mg/m 2 for five days intravenous, every three weeks until disease progression, or intolerable toxicity, or death. We reported the preliminary results for potential benefits in this new treatment. The primary endpoint was prostate specific antigen (PSA) response rate, defined as a 50% or greater reduction in serum PSA. The secondary endpoint included investigators-assessed objective response rate (ORR) and disease control rate (DCR) according to RECIST v1.1, radiographic progression-free survival (rPFS) according to PCWG3 criteria, overall survival (OS), and safety. The trial was registered at Chinese Clinical Trial Registry (No. ChiCTR2200061635). Results: By January 31 st , 2024, twenty-five mCRPC patients with a median age of 67 years were enrolled in this study at Sun Yat-sen University Cancer Center since March 23 rd , 2022. Patients received an average of 4.2 lines of prior anticancer treatments: 100% of them received docetaxel, 96.0% of them received abiraterone, and 80.0% progressed after enzalutamide, and/or apalutamide. 28.0% of patients had visceral metastases, and 88.0% patients had bone metastases. At of the cut-off date, the PSA response rate was 16.0%. The median rPFS and OS were 4.9 months and 7.1 months, respectively. One patient had a durable response for 19.2 months and had been remaining on study treatment to date. One PR and four SD were observed in ten patients with measurable lesions, resulting in an overall ORR and DCR of 10.0% and 50.0%, respectively. The most common treatment-related adverse events (TRAEs) including peripheral sensory neuropathy (76.0%), dyspepsia (72.0%), anemia (64.0%), constipation (60.0%), fatigue (64.0%), nausea (36.0%), leukocytopenia (32.0%), arthralgia (32.0%), dizziness (32.0%), vomiting (20.0%), and diarrhea (20.0%) were manageable. The 3/4 grade TRAEs included anemia (16.0%), and diarrhea (4%). No treatment-related death occurred. Conclusions: UTD1 has demonstrated promising efficacy and favorable tolerance in heavily pretreated mCRPC patients after progression on docetaxel in the preliminary analyses. Additional randomized trials are warranted for this new regimen. Clinical trial information: ChiCTR2200061635.