PROM1 and cancer: Metformin decreases the expression of cancer stem cell related genes associated with pluripotency, self-renewal and the Hippo pathway, including SOX9, β-catenin and YAP1, and appears to reduce the proportion of ALDHhigh ovarian cancer cells and CD133+ve pancreatic cancer cells at a concentration that does not affect the proliferation of whole tumour cell lines [31,32,33,34,35].