PIK3CA and cancer: However, relatively few drugs targeting these pathways have been discovered by drug repurposing.56,57 Remarkably, cancer cells may also circumvent pathways that need ligand-mediated receptor induction to sustain proliferative signal, instead relying heavily on three important pro-survival signaling pathways: PI3K/AKT, mTOR, and MAPK/ERK.58,59 An ever-increasing number of non-oncology drugs have been repurposed to treat cancer by effective inhibition of these pathways.