Hypoxia increases tumor-initiating or cancer stem cell (CSC) numbers in many cancers as small subsets of stem-like cells showing a greater capacity for self-renewal, pluripotency, differentiation and initiation of new tumors [13,14,15,16], in a process mediated by HIF-2α and its targets Oct-4, c-Myc and Nanog [17]. Here, EPAS1 is linked to cancer.