Cancer Stem Cells: Current Concepts and Therapeutic Implications

Cancer stem cells are the cells in a tumor that possess the capacity for self-renewal and to produce the heterogeneous lineages of cancer cells that compromise the tumor, act like normal stem cells, and render tumors resistant to chemotherapy. Like normal stem cells, cancer stem cells are marked by their ability to unlimited self-renewal, to differentiate, and to regenerate a phenocopy of the original tissue. In addition to playing a role in primary tumor formation, it has been shown that cancer stem cells are also key players in the metastatic process, with their unlimited capacity for self-renewal, the requirement for a specific microenvironment in which to grow, use of the CXCL12/CXCR4 axis for homing and quiescence. They also enhance resistance to apoptosis and have an increased capacity for drug resistance. Developing targeted therapies that are selectively toxic to cancer stem cells, and their microenvironment while sparing normal stem cells may lead to more effective treatment options for eradicating this crucial population of cells.