A randomized phase II study of pazopanib in castrate-sensitive prostate cancer: A University of Chicago phase II consortium/DoD Prostate Cancer Clinical Trials Consortium study.

Abstract

170 Background: Intermittent androgen suppression (IAS) has been studied as a way of minimizing toxicity from long term androgen deprivation therapy (ADT). Based on previous studies with similar agents, we hypothesized that inhibition of VEGFR would result in prolonged time to PSA progression (TTPP) and allow for longer periods off ADT. Methods: Men with biochemically recurrent, progressive prostate cancer and no evidence of macroscopic metastases were enrolled. They received 6 months of ADT. If at the end of that time the PSA was <0.5 ng/mL (with castrate testosterone levels), they were randomized to pazopanib 800 mg/d or observation. The primary outcome was TTPP, defined as time to a PSA >4.0 ng/mL, at which time they were restarted on ADT. Results: 37 pts met randomization criteria. 18 were randomized to pazopanib. Only 4 pts met the endpoint criteria of TTPP, whereas 13 (72%) pts went off study for other reasons with 1 pt on treatment at study closure. Reasons for discontinuation included drug toxicity (grade 1/2, 9 pts) and patient preference (2 pts). No grade 3/4 toxicity was noted. 1 pt was removed due to pulmonary embolus, 1 pt due to MD discretion and 1 pt due to noncompliance. 19 pts were randomized to observation of which 12 were off treatment when the study was stopped. Only 5 pts met criteria for TTPP, whereas 7 of 12 (58%) dropped out for other reasons, including the frequency of protocol related blood draws and visits (3 pts) and randomization to observation (2 pts), 1 pt was removed per MD discretion and 1 pt transferred care. Due to high dropout rates in both arms, accrual was halted as the primary endpoint could not be measured robustly. Conclusions: Minimizing the long term toxicities of ADT is an unmet need in prostate cancer therapy. Hence clinical interventions in concert with IAS represent an attractive area for drug development. This trial has outlined several barriers that exist in studying this patient population and might help to optimize future studies. Future trial design in this arena should investigate drugs with minimal toxicity and employ a design that maximizes patient convenience while anticipating the low threshold for patient drop out. No significant financial relationships to disclose.