Development and analytic validation of an ARv7 / PSMA dual biomarker circulating tumor cell assay
Prostate cancer drug targets and biomarkers that plasma cfDNA cannot report are carried on circulating tumor cells; this AACR 2024 poster describes the development and analytic validation of a dual biomarker assay that measures ARv7 and PSMA expression on the same individual CTC.
Presented by RareCyte.
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- Sensitivity and specificity were measured on spiked model cell lines, not on patient CTCs. Known positive and negative cell lines spiked into normal donor blood gave 83% sensitivity and 98% specificity for ARv7 (22Rv1 against BT474), and 97% and 99% for PSMA (LNCaP against PC3), aggregated over more than 1000 model CTCs from 15 tested slides in each population run on 3 separate days. These are per-cell biomarker-call rates on cells the workflow had already recovered, not CTC detection rates.
- Both biomarkers are read on the same individual CTC, and the phenotypes came apart. With per-cell positivity thresholds of MFI 140 for ARv7 and MFI 200 for PSMA applied across nine Stage IV prostate cancer samples, patient #2 ran 96.5% ARv7-positive and 0% PSMA-positive over 384 CTCs, while patient #8 ran 27.9% ARv7-positive and 98.8% PSMA-positive over 86 CTCs — the only two samples with more than nine CTCs recovered.
- The nine-sample patient series was run to demonstrate feasibility, and the performance claim stays with the cell lines. CTC counts ranged from 1 to 384 per sample; blood was collected into AccuCyte tubes, density-separated and spread to slides, stained on a Leica BOND RX, scanned on CyteFinder, confirmed by a trained reviewer, then scored in CyteMapper. The poster reports no patient outcomes and no treatment comparison.
