Circulating Tumor Cells, Cancer Stem Cells, and Emerging Microfluidic Detection Technologies With Clinical Applications

Metastasis is at the root of over 90% of cancer deaths, making the cells in the intermediate step of traveling through the bloodstream an area of active research. A subset of these circulating tumor cells (CTCs) may exhibit the highly plastic properties of cancer stem cells (CSCs). Given parallels between these important subsets of tumor cells, technologies have been developed for their isolation and study. Improvements on initial macroscale technologies occurred with the introduction of microfluidics to the field. Successive technologies have used different materials, chemistries, antigen expression patterns, and physical properties to separate CTCs with high specificity, sensitivity, purity, and throughput. Simultaneously, a main objective in the field is to enable the downstream analysis necessary to obtain the most information from these cells and demonstrate their use in the clinic. Addressing heterogeneity is a major challenge in this promising, but still young, field of research.