Abstract C88: A novel multiplex RNA in situ hybridization (ISH)-based method for circulating tumor cell detection with demonstrated clinical utility for metastatic breast cancer.

Abstract

Abstract Purpose: Sensitive and specific detection of circulating tumor cells (CTCs) in a blood sample is required for realizing the full potential of CTCs as prognostic and predictive factors. Current approaches of CTC detection are largely ineffective, and are dependent on the presence of differential epithelial protein markers or upon crude morphological characteristics like cell size differences between CTCs and blood cells. These combined approaches do not detect all relevant CTCs due to their significant heterogeneity. The objectives of this study are to develop and characterize a novel RNA in situ hybridization (ISH)-based CTC detection system called CTCscope, and to demonstrate its potential clinical utility in metastatic breast cancer patients. Experimental Design: Cultured cells of different cancer cell lines were spiked into whole blood, which was used as a model system for CTCscope development. A novel ultrasensitive fluorescent RNA-ISH method was used to detect mRNA transcripts of a multitude of tumor markers at single-cell resolution. To demonstrate feasibility of CTC detection in patient blood, duplicate blood samples were collected from 45 metastatic breast cancer patients with informed consent for CTC analysis by the newly developed CTCscope system and the CellSearch system. Association of CTCs with tumor marker CA15–3 and progression-free survival (PFS) was assessed. Results: CTCscope detected mRNA transcripts of 8 epithelial tumor markers and 3 epithelial-mesenchymal-transition (EMT) markers, and resulted in increased sensitivity for CTC detection. CTCscope was used to detect CTCs without enrichment, and did not result in false positives from detection of apoptotic or dead cells. In patient blood samples, CTCs detected by CellSearch but not CTCscope were positively correlated with CA15–3 levels. CTCs detected by either CTCscope or CellSearch predicted PFS, but only CTCs detected by CTCscope remained significantly associated with PFS (hazard ratio 2.01, 95% CI 1.14–3.92, p=0.038) after adjusting for CA15–3 levels. Conclusions: The CTCscope assay may offer unique advantages over existing CTC detection approaches. By enumerating and characterizing only viable CTCs, CTCscope may provide additional prognostic and predictive information. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C88.