  The cancer stem cell theory in part is descended from the view that cancers are in several ways akin to ordinary tissue (though distorted), containing a mixture of proliferating stem cells and their more differentiated products. This view played an important role in cancer research in the 1960s and 1970s, and is sometimes called the  “developmental” theory of cancer, in light of the fact that it takes cancer to be a disease of “development,” or cellular differentiation in particular (Pierce &amp; Speers 1988, Morange 2015, Laplane 2016). This model of cancer etiology was revived in the 90s, when Lapidot, Bonnet, and Dick identified “leukemic stem cells” (Lapidot, et al. 1994, Bonnet and Dick 1997), and was expanded upon in the early 2000s with the identification of an analogous cell population in breast cancer, suggesting that CSCs are a general feature of all cancers (Al-Hajj, et al. 2003). 