A randomized phase II study of pelareorep (REO) plus docetaxel vs. docetaxel alone in patients with metastatic castration resistant prostate cancer (mCRPC): Canadian Cancer Trials Group study IND 209.

5021 Background: Pelareorep (REO) is an oncolytic virus with in vitro and in vivo activity in many cancers, including prostate. It has in vitro synergism with microtubule targeted agents especially taxanes. We undertook a clinical trial to evaluate REO in mCRPC patients (pts) receiving docetaxel. Methods: In this randomized, open-label multicenter phase II study, pts received docetaxel 75mg/m2 on day 1 of a 21-day cycle in combination with REO given as 3x1010 TCID50 IV daily on days 1-5 (arm A), or alone (arm B). The primary endpoint was 12-week lack of disease progression (LPD) rate. Secondary endpoints included objective response rate; survival; circulating tumor cell (CTC) enumeration at 0, 6 and 12 weeks; PSA response rate and biomarkers. Results: Eighty-five pts were randomized. Median age was 69, ECOG performance status (PS) was 0/1/2 in 31%/66%/3% of pts. Bone/regional lymph node/liver metastases were present in 98%/24%/6% of pts. More pts in arm A had poor prognostic factors for survival at baseline (median prognostic index 1.44 vs. 1.29). The median number of cycles delivered for arms A/B was 7/9 (range 1-10 and 1-13). In arm A, 51%/68% of pts received ≥90% of planned dose intensity of docetaxel/REO respectively, vs. 76% of pts for docetaxel in arm B. Adverse events (AE) were as expected for docetaxel therapy but more prevalent in arm A (grade 3 or higher all AEs 80 vs. 74%). A higher rate of grade 4 febrile neutropenia was noted in arm A (7 vs. 0%) but may represent virus related fevers. The 12-week LPD rate was 61% and 52.4% in A/B respectively (p = 0.51). OS was worse in arm A vs. B (HR 1.95; 95% CI 0.94-4.06; p = 0.07 after adjusting for age, PS and baseline prognostic score). There was no difference between arms in CTC favourable status at any timepoint. No survival benefit of REO with D was found in any subset from the biomarker analysis. Conclusions: While the combination of REO with D for patients with mCRPC was tolerable and LPD rate was comparable in both arms, docetaxel dose intensity and survival were inferior and so this combination, as tested, does not merit further study. Clinical trial information: NCT01619813.