ABSTRACT
The experimental demonstration of cancer stem cells (CSCs) in a variety of human malignant tumors, including cancers of the blood, breast, brain, bone, skin, liver, lung, bladder, ovary, prostate, colon, pancreas and head and neck has led to the conceptual hypothesis that tumors, like physiologic proliferative tissues, can be hierarchically organized and propagated by limited numbers of dedicated stem cells (Reya et al. 2001, Pardal et al. 2003, Dick 2008, Frank et al. 2010, Hermann et al. 2010, Clevers 2011, Nguyen et al. 2012). According to a consensus defi nition, these CSCs are cells within a tumor that possess the capacity to self-renew and to give rise to the heterogeneous lineages of cancer cells that comprise the tumor (Clarke et al. 2006). CSCs can therefore only be defi ned experimentally by their ability to recapitulate the generation of a continuously growing tumor in serial xenotransplantation settings (Clarke et al. 2006).
