Cancer stem cells, cancer-initiating cells and methods for their detection.

The cancer stem cell (CSC) hypothesis considers CSCs as the main culprits of tumor initiation, propagation, metastasis and therapy failure. CSCs represent a minority subpopulation of cells within a tumor. Their detection, characterization and monitoring are crucial steps toward a better understanding of the biological roles of these special cells in the development and propagation of tumors which, in turn, improves clinical reasoning and treatment options. Nowadays, in vitro and in vivo assays are available that address the self-renewal and differentiation potential of CSCs, and advanced in vivo molecular imaging technology facilitates the detection and provides an unprecedented in vivo observation platform to study the behavior of CSCs in their natural environment. Here, we provide a brief overview of CSCs and describe modern cellular models and labeling techniques to study and trace CSCs.