Cancer Stem Cells: A Revisitation of the “Anaplasia” Concept. In Advances in Cancer Stem Cell Biology

Cancer stem cells are a subpopulation of cancer cells within a tumor originally characterized by the capability of initiating colonies in vitro or of forming tumors at high efficiency when injected into immunocompromised NOD/SCID mice. These cells have an undifferentiated phenotype and resemble normal stem cells in many ways, but are no longer under homeostatic control. Cancer stem cell hypothesis permit to justify some intriguing and debated aspects of clinical oncology (radio- and chemoresistance, recidivism and metastasis). The definition of functional properties (cluster of differentiation, aberrant signaling pathways, high expression of drug efflux pumps of the MDR family, ALDH) of cancer stem cells not only may permit their identification and isolation, but could permit to understand the mechanisms at the basis of their genomic and phenotypic instability. These peculiarities seem to induce a lethal genomic and phenotypic plasticity that is the molecular basis of cancer aggressiveness. The understanding of this high adaptability of cancer stem cell must represent the real target for a valid therapeutic and diagnostic approach to cancer.