<b>Pilot Study of CTC Enumeration and AR-V7 Detection Using a Microporous Chip Filtration System in Metastatic Prostate Cancer</b>

BACKGROUND: Circulating tumor cells (CTCs) provide intact molecular and phenotypic information and serve as key liquid biopsy targets, especially for detecting androgen receptor splice variant 7 (AR-V7), a marker of resistance to androgen receptor pathway inhibitors (ARPI) in prostate cancer. This study was conducted to evaluate the feasibility of AR-V7 detection in CTCs and to verify the clinical correlation between CTC counts, AR-V7 expression, and ARPI resistance in patients with metastatic prostate cancer (mPCa) using CytoGen’s Smart BiopsyTM platform. METHODS: Peripheral blood samples from 12 patients with advanced prostate cancer were collected and processed for CTC enrichment and analysis, including CTC enumeration using immunofluorescence (IF) and AR-V7 detection using droplet digital PCR (ddPCR). Five samples from healthy donors were used as negative controls, and the threshold for AR-V7 expression was established for ddPCR. Clinical association was assessed by comparing CTC counts or AR-V7 detection in CTCs with clinical outcomes. RESULTS: CTCs were successfully enumerated and validated in all 12 samples using IF. ddPCR enabled sensitive detection of AR-V7 transcripts in a subset of samples, with spiking tests confirming analytical sensitivity. Ten patients had a high CTC burden (≥10 CTCs per 5 mL of blood), with a statistically significant association with ARPI resistance (33.3% vs 100%, p=0.046). Five patients showed AR-V7-positive CTCs, and four of these patients demonstrated a poor response to ARPI therapy. CONCLUSIONS: This study highlights the feasibility of a CTC-based liquid biopsy using a high-density microporous chip platform that can isolate all CTC types to predict treatment response to ARPI through CTC counts and/or AR-V7 detection in CTCs, supporting its potential as a clinically applicable assay to guide therapeutic decisions in patients with mPCa.