223P - The Analytical Validation of Prostate Specific Mrna Detection in Whole Blood by Reverse Transcription-Polymerase Chain Reaction (RT-PCR) as a Prognostic Biomarker for Patients with Castration-Resistant Prostate Cancer (CRPC)

Abstract

ABSTRACT Background To estimate the association between molecular biomarkers and outcomes, robust assays are needed before qualification in prospective trials. Although tumor specific transcripts detected in blood by PCR have been associated with clinical outcome, an analytically validated PCR platform enabling detection of CTC-associated transcripts in clinical settings remains to be identified. Here we explore the efficacy of detecting a panel of prostate specific transcripts in conjunction with conventional markers in CRPC. Method Blood was collected from 97 patients with progressive CRPC in PAXgene tubes (2.5 ml) for total RNA extraction using PAXgene Blood RNA Kit. Five genes expressed in prostate but not in nucleated blood cells were analyzed by primer-specific RT-PCR. We used a Fluidigm Dynamic Array platform to analytically validate RT-PCR assays for KLK3, KLK2, HOXB13, GHRL2 and FOXA1 transcripts. Each PCR-reaction was run in 6 replicates, detection thresholds for each gene were chosen by ROC analysis of an independent set of 56 CRPC patients versus 51 healthy volunteers, and results were reported as transcripts present or absent. CellSearch reported CTC number/7.5 ml of blood drawn into CellSave tube. Result Prostate specific transcripts were detected in 70/97 (72%, 95% CI 62-80%) of patients with progressive CRPC studied with a median survival time of 17 months (95% CI: 13.8, 23.5). 42/45 CRPC-patients with ≥5 CTC and 28/52 CRPC patients with Factor log Rel Risk se(log Rel Risk) p-value LDH (≥300) 1.460 0.345 Any prostate specific transcript present -0.850 0.318 0.008 The predictive accuracy (CPE) of transcript detection + LDH was 0.756 (SE 0.043), comparable to CTC-enumeration + LDH (0.796, SE 0.035). Conclusion The detection of prostate specific transcripts in whole blood using validated RT-PCR assays, applicable to larger CRPC cohorts, is prognostic for overall survival. The clinical utility of this test in monitoring treatment will be explored prospectively. Disclosure All authors have declared no conflicts of interest.