Efficacy and safety of single-agent pertuzumab (rhuMAb 2C4), a human epidermal growth factor receptor dimerization inhibitor, in castration-resistant prostate cancer after progression from taxane-based therapy

Purpose: Pertuzumab represents a new class of targeted anticancer agents, human epidermal growth factor receptor (HER) dimerization inhibitors. The aim of this single-arm phase II clinical study was to assess the efficacy and safety of single-agent pertuzumab in castration-resistant prostate cancer (CRPC) patients who had experienced progression after prior chemotherapy. Patients and Methods: Patients received pertuzumab every 3 weeks. All castration-resistant patients had experienced progression after at least one taxane-based regimen. Patients received a loading dose of 840 mg pertuzumab (cycle 1) followed by 420 mg for subsequent cycles. The primary end point was overall response and safety. A separate retrospective analysis of actual survival time versus predicted survival time for a patient population with comparable prognostic features was performed. Results: Patients were enrolled (N = 42) and treated (n = 41). No patients had complete or partial response (as defined by Response Evaluation Criteria in Solid Tumors Group or ≥ 50% decline in prostate-specific antigen). Of 30 efficacy-assessable patients, five had stable disease (SD) for at least 23 weeks; one of five had SD for 36 weeks. Pertuzumab was well tolerated; diarrhea was the most common adverse effect (61.0%, grades 1 to 3). Retrospective analysis of survival using a validated nomogram suggested that survival was prolonged with pertuzumab treatment, compared with historic controls with similar baseline prognostic features. Conclusion: Pertuzumab was well tolerated and resulted in no objective responses, but several patients had SD more than 23 weeks from a heavily pretreated population. Retrospective analysis suggested prolonged median survival time with pertuzumab compared with historical controls. Thus, inhibition of HER dimerization may have clinical utility in CRPC patients.