A multiparameter assay for HER2 protein detection on circulating tumor cells in non-small cell lung cancer
Lung tumor biopsy carries a 30% adverse event risk and often yields too little material to test, so this AACR 2020 poster reports an immunofluorescence assay that measures HER2 protein on circulating tumor cells from a blood draw — analytically validated on spiked model CTCs, then applied to 10 NSCLC patient samples.
Presented by RareCyte / Pfizer.
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- Sensitivity ran 1.000, 0.999, 0.975 and 0.944 across the four HER2-positive cell lines, against a specificity of 0.968 on the HER2-negative line. Five lines spanning HER2-high (BT-474) to HER2-negative (MDA-MB-468) were spiked into blood and scored cell by cell at a fluorescence intensity threshold of 41, set two standard deviations above the negative line’s mean. These are analytical figures measured on spiked model CTCs, not clinical performance in patients.
- MDA-MB-453, the only line run at both incubation times, held 99.9% HER2-positive from 24 to 72 hours in the collection tube. Mean per-cell HER2 intensity was 1329.5 at 24 hours and 1214.0 at 72 hours. Each blood draw was processed to 8 slides on the AccuCyte system, stained with the RarePlex HER2 CTC kit, scanned on CyteFinder, and scored per cell by CyteMapper software.
- In 10 post-treatment NSCLC blood samples, at least one CTC was found in 6, and HER2 expression was confirmed in 5 of those 6. CTC counts ranged from 0 to 2043 per 7.5 mL. The scoring threshold was raised to an intensity of 100 on patient slides because of higher non-specific background staining, and the authors conclude that a larger clinical sample set is needed to determine optimal clinical thresholds.
