An In-Depth Evaluation of the Validity and Logistics Surrounding the Testing of AR-V7 mRNA Expression in Circulating Tumor Cells

Recent reports have emphasized the clinical relevance of detecting AR-V7 in circulating tumor cells (CTCs). Our aim was to set up a validated multicenter pipeline to measure AR-V7 by quantitative RT-PCR (RT-qPCR) in RNA isolated from CellSearch-enriched CTCs to provide an AR-V7 –positive or AR-V7 –negative score in a clinically acceptable time range. CellSearch-enirched CTCs from patients with metastatic castration–resistant prostate cancer were characterized by RT-qPCR. After optimization, it was prospectively tested whether it was possible to report the AR-V7 status within 11 days (PRELUDE study). In the range of the RNA equivalent of 0.2 to 12 VCaP cells, the CV for AR-V7 was 9% ( n  = 37). The limit of detection was 0.3, and the limit of quantitation was 3 cells in the final RT-qPCR. No differences were observed between AR-V7 data generated by five technicians or in two different laboratories. For the 45 patients in PRELUDE, 13 patients were ineligible, 22 patients were AR-V7 negative, and 10 were AR-V7 positive. The median time to inform the physician of the test result was 7 days (range, 2 to 11 days). This assay can establish the AR-V7 status in CTCs from patients with metastatic castration–resistant prostate cancer. Furthermore, it was possible to provide an AR-V7 outcome within 11 days, indicating that it may be used to choose between an anti–androgen receptor or taxane-based cabazitaxel treatment.