Abstract 1033: Evaluation of HER2 status in circulating tumor cells isolated using the Parsortix® system

Abstract Background: Evaluation of HER2 status in tissue from breast cancer patients is a standard test for clinical diagnosis and treatment. However, tissue biopsy is invasive and repeated testing is generally not possible. Liquid biopsy allows minimally invasive, repeat sample collection for regular monitoring. This study combined ANGLE’s Parsortix® PR1 Research System*, an epitope-independent microfluidic device that isolates and harvests rare cells from blood based on size and deformability, with two downstream assays: an Immunofluorescence (IF) assay for HER2 protein detection and an IF assay combined with FISH targeting HER2 gene amplification, to determine HER2 status on circulating tumor cells (CTCs). Methods: Blood was collected from healthy volunteers into Streck Cell-Free DNA tubes. Two aliquots of blood from each donor were spiked with cultured SKBR3 (HER2+) and Hs 578T (HER2-) breast cancer cells and then processed using Parsortix® PR1 instruments. Captured cells were harvested and spun onto positively charged slides. One slide per donor was stained using ANGLE’s IF panel for CTC detection, consisting of a nuclear dye, antibodies targeting epithelial and mesenchymal markers, and antibodies targeting blood cell markers. After imaging, slides were de-stained and processed using a commercially available HER2 FISH kit. Cancer cells identified by the IF panel were re-imaged to examine FISH signal. Cells were considered HER2+ if the ratio of HER2 foci to CEP17 foci was ≥2. The second slide was stained using the same IF CTC panel in combination with an antibody targeting HER2 protein. HER2 expression was analyzed based on intensity of fluorescence signal. Same workflow was implemented in a small cohort of breast cancer patients with blood processed 72-144 hours post-draw using Parsortix® PC1 Clinical System. Results: The numbers of epithelial and mesenchymal CTCs detected on each slide were comparable in both assays. In HER2 FISH-stained samples, 97.3% of the SKBR3 cells and 13.3% of the Hs 578T cells harvested showed HER2 amplification. This data was consistent with the literature (~20% of Hs 578T cells tend to form isochromosomes, altering the HER2/CEP17 ratio). In IF-only stained samples, 96.8% of the SKBR3 cells and 0% of the Hs578T cells harvested overexpressed HER2 protein. In patient samples, CTCs were identified in 80% of the donors (mean: 21; median: 6; range: 0-200), with 17% of the CTC-positive donors having ≥1 CTC overexpressing HER2 protein. Conclusions: This study demonstrates the feasibility of HER2 evaluation using IF for protein expression and HER2 FISH for gene amplification on CTCs enriched from blood using the Parsortix® systems. It also demonstrates that blood collection in Streck tubes is suitable for both assays, with the advantage of allowing longer blood sample storage and facilitating batch shipping and processing of clinical samples. *Research Use Only. Not for use in diagnostic procedures. Citation Format: Nerea Borreguero-Munoz, Alex Young, Jessica Kimber, Mariacristina Ciccioli, Anne-Sophie Pailhes-Jimenez. Evaluation of HER2 status in circulating tumor cells isolated using the Parsortix® system [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1033.