Phase II trial of intravenous carboplatin (C), oral everolimus (E), and prednisone (P) in docetaxel-pretreated (DP) metastatic castrate-resistant prostate cancer (mCRPC): A Prostate Cancer Clinical Trials Consortium study.

Abstract

5041 Background: A phase II clinical trial was conducted of the combination of C and E due to the synergy noted. Methods: The primary endpoint was time to progression (TTP). Intravenous C at a target AUC of 5 on day 1, and oral E 5mg once daily and P 5mg twice daily were administered in 21 day cycles. PSA was assessed every 21 days and radiologic response was assessed every 3 cycles. Secondary endpoints included overall survival (OS), the correlation of TTP with phosphorylated (p) mTOR, pAKT, p70S6, and circulating tumor cells (CTC). A 1-stage study design assumed: a reference median TTP = 1.5 months; 1-sided alpha = 0.15; and power = 0.90, requiring 26 patients (pts). Results: 26 pts enrolled; median age 69 years (range 54-86) ;8 African American and 18 Caucasians. Median pretherapy PSA was 190 ng/ml (range 13 - 2174). 18 pts (69%) each had bone pain and Gleason score > 8. 125 cycles have been administered; median 3 cycles (range 1 - 16). Predominant grade 3 or 4 toxicities were thrombocytopenia in 8 pts, pulmonary embolism in 2 and neutropenia in 3. No treatment related deaths occurred. 4 (15%) had a > 30% PSA decline and 1 had a >90% PSA decline. 8/19 pts had stable disease but no objective responses in MD. The median TTP and OS were 2.5 months (90% CI: 1.8 - 4.3), and 12.5 months (90% CI: 6.7 - 16.1), respectively. Median area under curves were 5.9 (range, 4.3 – 11.0) and 4.5 (range, 4.1 – 7.1) mg/mL*min with C given alone and in combination with E, respectively. E did not influence pharmacokinetics of C. Median baseline CTC (n=18) was 30 (range 0-2372). 5/18 pts had favorable CTC (CTC<5/7.5 mL) pretherapy. Patients with TTP >18 weeks had reduction in post-therapy CTC with a median decrease of 63% (range 11%-100%). Lack of IHC staining for pAKT was noted in 2/2 pts on therapy for > 30 weeks vs increased expression was noted in 8/8 pts on therapy for < 9 weeks. Testing for TSC1 mutation is planned and will be reported. Conclusions: The combination was tolerable but revealed modest clinical efficacy. Biomarker evaluations such as pAKT may help identify a subset likely to benefit from mTOR inhibitor strategy in mCRPC. Clinical trial information: NCT01051570.