Whole blood FOLH1 mRNA expression and treatment response in metastatic castration-resistant prostate cancer (mCRPC)

188Background: Identifying predictive biomarkers for mCRPC patients receiving androgen receptor signalling inhibitors (ARSI) or chemotherapy remains an unmet clinical need. FOLH1 encodes for Prostate-Specific Membrane Antigen (PSMA), a type II glycoprotein highly expressed on prostate cancer cells. We designed a whole blood assay to detect FOLH1 mRNA, and correlated expression with clinical outcomes in patients commencing ARSI (abiraterone or enzalutamide) or chemotherapy (docetaxel or cabazitaxel). Methods: mCRPC patients commencing ARSI or chemotherapy were prospectively recruited at three Australian centres from June 2016 to July 2018. A quantitative reverse transcription polymerase chain reaction assay was used to detect FOLH1 transcript from whole blood samples collected in PAXgene® RNA tubes. Pre-treatment FOLH1 expression was correlated with PSA response rate (Fisher’s exact test) and PSA progression-free survival (PSA-PFS) (log-rank test). Results: Median follow-up was 13.6 months (IQR 9.7–19.3). ...