Phase 2 study of circulating microRNA biomarkers in castration-resistant prostate cancer

Background: Biomarkers of therapeutic response and prognosis are needed to assist in the sequencing of treatments for metastatic castration-resistant prostate cancer (CRPC). Previously in a Phase 1 discovery study, we identified 14 circulating microRNAs that were associated with response to docetaxel chemotherapy or overall survival. We performed a Phase 2 validation study to verify these findings. Methods: Using real-Time PCR, the levels of the 14 microRNAs were measured in plasma collected before and after the first cycle of docetaxel from a Phase 2 cohort of 89 patients. Results: The microRNAs were not associated with docetaxel response in the Phase 2 cohort. Higher baseline levels of six microRNAs, predominantly of the miR-200 family, were confirmed to be associated with shorter overall survival. A microRNA signature comprising these six microRNAs predicted high-risk patients in the Phase 2 cohort with a hazard ratio of 4.12 (95% CI 2.20-7.70, P=0.000001). The signature was an independent predictor in multivariable analysis with clinicopathological factors. Conclusions: The association of circulating microRNAs with overall survival suggests their involvement in CRPC progression.