Abstract 4955: Isolation and characterization of circulating tumor cells (CTCs) in breast and prostate cancer: Comparison of Harpoon CTC assay performance with the CellSearch CTC Test

Abstract

Abstract Circulating tumor cells (CTCs) can provide important information about a patient's prognosis. Currently, the CELLSEARCH® CTC Test (hereafter referred to as CS) is the only US Food and Drug Administration-cleared assay for isolating and enumerating CTCs. This technology uses a CTC antigen-dependent method to isolate CTCs that may limit its ability to detect CTCs with low or no epithelial cell adhesion molecule (EpCAM) expression. We evaluated the Harpoon CTC Isolator and Chip, which uses an antigen-independent, negative depletion method to enrich CTCs from patient blood samples. As a result of the negative depletion method, the final Harpoon Product (ie, CTC-enriched cell suspension) contains CTCs that express cytokeratin (CK) and EpCAM (canonical CTCs) as well as those with low or no expression of these antigens (non-canonical CTCs). After isolation, CTCs were spun onto microscope slides and imaged using a Vectra Multispectral Imaging System. We obtained performance data on an initial prototype Harpoon assay (Harpoon + Vectra [Hrp+Vec]) and compared CTC enumeration between Hrp+Vec and CS using blood samples from 36 breast and prostate cancer patients. From 7.5 mLs of blood, the Hrp+Vec assay recovered 79.0% to 93.5% of canonical EpCAM+/CK+ CTCs recovered by CS. The Hrp+Vec assay also successfully detected non-canonical CTCs (EpCAM-/CK+ or EpCAM+/CK-) in these samples. At the CS clinical cutoff for prognostic value, where ≥5 CTCs is associated with poor prognosis, the Hrp+Vec assay was 97% concordant with CS. Hrp+Vec also detected CTCs in 12.5% (2/16) more patient samples than CS. Finally, a consensus analysis of all Vectra scan results (including both canonical and non-canonical CTCs) demonstrated that the Hrp+Vec assay detected between 90.5% and 108.9% of the number of CTCs as identified by CS. These results indicate that, when compared with CS, the prototype Hrp+Vec assay detected CTCs with similar efficiency and identified more samples as CTC-positive in these breast and prostate cancer patients. Importantly, the Hrp+Vec assay did enrich non-canonical CTCs thought to be missed by CS, and ongoing efforts are aimed to further characterize these cell populations. Citation Format: Mark Connelly, David Chianese, Carrie Morano, Thai Bui, Shemeeakah Powell, Noel Ngoubilly, Renouard Sanders, Tom Barber, Ravi Kapur, Shyamala Maheswaran, Mehmet Toner, Daniel Haber. Isolation and characterization of circulating tumor cells (CTCs) in breast and prostate cancer: Comparison of Harpoon CTC assay performance with the CellSearch CTC Test. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4955.