Phase II study of sorafenib and docetaxel in men with metastatic castration resistant prostate cancer (mCRPC)
e16055 Background: Previous trials of the antiangiogenic kinase inhibitor sorafenib in mCRPC have reported PSA elevation accompanying radiographic response, and evidence that sorafenib may potentiate docetaxel (dxl) myelosuppression. To assess the safety, antivascular effects, and activity of sorafenib and dxl in mCRPC, a phase II trial with dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI) was conducted. Methods: Eligible men had mCRPC and no prior chemotherapy. Treatment consisted of dxl 75 mg/m2(day 1) and sorafenib (days 2–19) of a 21 day cycle. Patients received 7 days of sorafenib before cycle 1. Six patients received sorafenib 200mg BID and remaining patients received sorafenib 400 mg BID if <4/6 patients had grade 4 neutropenia. DCE-MRI was performed at baseline, days 8 and 28. The primary endpoint was PSA response rate (>50% PSA decline). Secondary endpoints were vascular response rate (>20% decline in area under the gadolinium curve [AUC60]), toxicity rates, and time to progression (TTP). PSA-only progression (2 consecutive PSA rises) was confirmed by a third PSA rise or radiographic progression after a 21-day drug holiday. Sample size of 69 patients in 1 stage was designed to maximize detection of significant correlations between DCE-MRI and clinical outcomes. Results: Six of 13 enrolled patients (46%) had a PSA response. A median PSA increase of 37% was observed in 73% of patients after 1 week of sorafenib. The median TTP was 8+ months. Two patients had complete disappearance of bone lesions. Grade 3 adverse events were neutropenia (77%), hand-foot syndrome (23%), anemia (15%), nausea (8%), and rash (8%). A median AUC60 decline of 40% from baseline was observed after 7 days of sorafenib, and only a 6% decline on day 28 during a scheduled sorafenib holiday. Conclusions: Sorafenib 400 mg po bid and dxl 75 mg/m2 are tolerable in men with mCRPC. Elevated PSA values in men treated with sorafenib and dxl does not always reflect disease progression. DCE-MRI can capture sorafenib's impairment of tumor vasculature in osseous metastases and rebound angiogenesis during drug holidays. Bone responses and TTP data provide evidence of encouraging activity. No significant financial relationships to disclose.