  Another major research program that in some ways challenges a mechanistic picture of cancer (or at least some (Laplane, 2016) see as opposed to the “classical view” of cancer) is the “cancer stem cell” theory (CSC).  However, the idea of cancer stem cells has been somewhat controversial, in part due to the experimental models used to establish and identify cancer stem cells. Fagan (2016) characterizes the notion of a cancer stem cell, as well as the current state of the field, succinctly as follows.