Abstract 2755: Comparison of blood based liquid biopsy methodologies for improved risk assessment of prostate cancer (PCa)
Authors: Rajpurohit Yashoda , Thomas Shibu , Patel Jaymala , Shen Dong , Gormley Michael , Smirnov Denis , Ricci Deborah 
Published: July 2017

Abstract
Approximately 28,000 men die from prostate cancer in the US each year. Predictive biomarkers can provide patient risk assessment to enable therapeutic decision making. Compared to tumor, blood based liquid biopsies offer greater flexibility for noninvasive sample collection and allows for continuous monitoring of treatment response. While various liquid biopsy sample types and methodologies are currently available, it is critical to identify which method offers the highest sensitivity and specificity for clinical decision making. In this study we systematically compared specificity and sensitivity of prostate cancer detection using a pre-selected panel of PCa specific mRNA transcripts using four different methodologies. In this prospective laboratory study, we collected five blood tubes from a cohort of 40 metastatic castrate resistant prostate cancer (mCRPC) patients and 20 age matched healthy volunteers (HV). Circulating tumor cells (CTCs) were enumerated and blood samples enriched for CTCs were isolated for mRNA evaluation. Two tubes of plasma samples were utilized to isolate exosomes using ExoRNAeasy columns and CellSearch EpCAM capture respectively, while RNA was extracted directly from whole blood collected in PAXgene tubes. RNA isolated from blood samples enriched for CTCs, two exosome preps and whole blood samples were tested using qPCR (Fluidigm) for a panel of 48 prostate specific mRNA transcripts and three endogenous controls previously shown to be detected in whole blood. Receiver operator analysis (ROC) was performed to compare expression of mRNA transcripts across all four methods. Results showed PCa specific genes were detected in whole blood, Exo-52 exosome prep and samples enriched for CTCs, while exosomes isolated using CellSearch EpCAM capture failed to detect any PCa transcripts. ROC showed ExoRNAeasy exosome prep detected PCa specific mRNA transcripts with significantly higher sensitivity and specificity compared to three other methodologies. Area under curve (AUC) for ExoRNA prep 0.65 to 0.75 (average of z score at 3.27 p= 0.0023), compared to AUC for PAXgene is 0.55 to 0.83, (average of z score at 2.64 and p=0.05) and CTC samples is 0.52 to 0.67, (average of z score at 1.63 and p= 0.19). For CellSearch exosome method, the AUC is 0.47 to 0.52, average of z score at 0.66 and p= 0.32). These early results support the utility of exosome derived mRNA assay as a viable alternative to whole blood and CTC based assays. Further testing for expression of markers associated with prognosis and treatment response is necessary to warrant its prognostic or predictive clinical utility.
Citation Format: Yashoda Rajpurohit, Shibu Thomas, Jaymala Patel, Dong Shen, Michael Gormley, Denis Smirnov, Deborah Ricci. Comparison of blood based liquid biopsy methodologies for improved risk assessment of prostate cancer (PCa) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2755. doi:10.1158/1538-7445.AM2017-2755