Validation of a dual-marker ARv7/SYP assay for CTC characterization
In prostate cancer, androgen receptor variant 7 (ARv7) and synaptophysin (SYP) each mark a less favorable prognosis — one tied to second-generation anti-androgen resistance, the other to neuroendocrine differentiation — and this NGDx 2020 poster reports the analytic validation of a research-use immunofluorescence assay that reads ARv7 and SYP on individual circulating tumor cells.
Presented by RareCyte and University of Washington.
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- A single immunofluorescence panel enumerates circulating tumor cells and characterizes two prostate-cancer markers on them. The dual-marker ARv7/SYP assay processes whole blood on the AccuCyte Sample Preparation System, stains slides with the RarePlex Staining Kit on a Leica BOND RX, and images on the CyteFinder Instrument; alongside a nuclear dye, antibodies to cytokeratin and EpCAM identify epithelial CTCs while CD45 excludes white blood cells, and ARv7 and SYP report the two biomarkers — all for research use only.
- On spike-in model cells, both markers were classified with high sensitivity and specificity. Using single-cell MFI thresholds of 180 for ARv7 and 120 for SYP against 22Rv1 (true-positive) and BT-474 (true-negative) cell lines, the assay reached 85% sensitivity and 92% specificity for ARv7 and 98% sensitivity and 96% specificity for SYP; inter-stainer-run precision coefficients of variation were 9.8% for ARv7 and 5.1% for SYP, both under 10%. These are per-cell classification rates on already-recovered model cells, not CTC detection rates.
- Applied to patient blood, the assay found circulating tumor cells positive for ARv7 or SYP. In clinical breast, colon and prostate cancer samples from patients known to have CTCs, subsets of cells were ARv7-positive or SYP-positive, with ARv7 localized to the nucleus and SYP to the cytoplasm as expected; the poster presents this as characterization of marker expression on patient CTCs, keeping the performance claim with the model-cell validation.
