Cancer stem cells: Paradigm shifting or perishing concept?

There has been tremendous progress in our understanding of intratumoral heterogeneity over the last decade. One emerging concept postulates that tumors are analogous to self-renewing adult tissues, and are maintained by a unique subpopulation of stem cells. Cancer stem cells are best defined functionally by their enriched tumorigenic properties, with distinct self-renewal and differentiation potential to regenerate the cellular heterogeneity of original patient tumors in immunocompromised mice. Cancer stem cells have attracted enormous attention in cancer research, and exploring their biology will provide tremendous opportunities to develop more effective therapeutic strategies against tumors. In this review, we summarize the historical perspective leading to the prospective isolation of CSCs, their intriguing biological characteristics and clinical implications with emphasis on solid tumors. We also discuss our perspectives on the controversies and possible misconcepts of the cancer stem cell model.