Abstract 1736: A novel RNA-based assay for the detection and monitoring of circulating tumor cell signatures in breast cancer

Examination of circulating tumor cells (CTCs) holds the potential of offering a real-time non-invasive window into tumor biology. Information gleaned from CTC detection and characterization can be used for early cancer detection, choice of therapy decisions and long-term monitoring for disease recurrence and the emergence of drug resistance mechanisms. However, technical difficulties with CTC isolation and the inherent limitations of imaging-based analysis have hindered the broad clinical use of CTCs as biomarkers. To overcome these concerns, we have combined our unbiased microfluidic CTC enrichment technology, the iChip, with a highly sensitive and specific multi-gene RNA-based biomarker panel to develop an assay that detects CTC signatures in patient blood samples in a high throughput and quantitative fashion. This assay was applied to a cohort of breast cancer patients, including women with both localized and metastatic disease. It successfully identified CTC signal in 50-70% of metastatic and 20-40% of localized pretreatment patient samples. Patient CTC scores, assigned based on a multi-marker prediction algorithm, correlated with cancer stage and grade, but not with hormone receptor status, suggesting the applicability of the assay to a wide range of breast cancer subtypes. To determine if CTC scoring was useful for disease monitoring, we performed monthly blood collection from metastatic patients starting a new line of treatment. CTC score as early as one month after initiation of therapy, but not at pretreatment, was predictive of progression-free survival and treatment outcome, suggesting that real-time kinetic changes in CTC signatures are more clinically informative that one-time static evaluation of their presence in a given sample. In addition, a subset of high-risk genes showed expression patterns over the course of treatment that highly correlated with disease recurrence. This observation indicates that a multi-marker panel can parse out dynamic changes in cancer gene expression programs and provide a molecular insight into treatment responses that are not achievable by assays built around one or few markers. In conclusion, our novel RNA-based method of identifying CTC signatures in liquid biopsies provides a sensitive platform for breast cancer detection and monitoring that goes beyond CTC enumeration. It offers a non-invasive quantitative molecular characterization of tumor gene expression that can be used to guide informed clinical decisions in both standard course of care and clinical trial settings. Citation Format: Tanya T. Kwan, Aditya Bardia, Tilak Sundaresan, Laura Spring, Mark Kalinich, David Miyamoto, Xin Hong, Joseph LiCausi, Uyen Ho, Sarah Javaid, Erin Silva, Lecia Sequist, Shyamala Maheswaran, Daniel Haber. A novel RNA-based assay for the detection and monitoring of circulating tumor cell signatures in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1736. doi:10.1158/1538-7445.AM2017-1736