HIF1A and neoplasm: HIF-1α deficiency inhibited overall tumor growth, whereas deficiency of HIF-2α stimulated tumor growth in colorectal cancers xenograft.28 HIF-1α and HIF-2α are differentially regulated in vivo and reflected distinctive protein expression patterns and stabilization mechanisms in HCC.15, 34 HIF-2α also appears to have a more general role in promoting tumorigenesis.