The HIF-1α and HIF-2α proteins are expressed in most types of human tumors, including breast, colon, ovarian, pancreatic, prostate, renal and hepatocellular cancers.14, 15, 16 Compared with surrounding normal tissues, HIF-1α or HIF-2α (or both) have been detected at higher levels in the majority of primary human cancers and their metastases.14, 15, 16, 17 HIF-2α mediates the adaptive response to decreased O2 availability at the cellular and organismal level. Here, EPAS1 is linked to cancer.