Quantitative Analysis of Circulating Tumor Cells Using RNA-Based Digital Scoring.

Circulating tumor cells (CTCs) provide valuable information about the molecular evolution of cancers, as they may initially respond and ultimately progress on therapy. As intact tumor cells isolated from the bloodstream, CTCs also enable assessment of heterogeneous subpopulations, and their analysis may include DNA, RNA, and protein biomarkers. New microfluidic cell isolation strategies greatly facilitate the challenge of enriching viable tumor cells from the billions of hematopoietic cells within a standard blood specimen. While counting and characterization of enriched CTCs have primarily relied on immunostaining for tumor cell-specific antigens, new RNA-based analytic platforms are providing new insight into the identity of CTCs and providing new tools for clinical applications. Single-cell RNA sequencing of CTCs reveals a high degree of heterogeneity among cancer cells from a single individual, while new digital RNA-based amplification platforms may now allow high-sensitivity and high-throughput quantitative scoring of CTCs for clinical applications. Here, we focus on transcriptomic analysis of CTCs and its relevance in understanding metastatic cancer progression and in developing diagnostic assays to monitor cancer.