HIF1A and neoplasm: Thus, while under normal oxygen conditions, HIF-1α activity is downregulated by HIF-P4H and FIH, and under conditions of hypoxia and oxidative stress or ascorbate deficiency, typical of tumors, HIF-P4H and FIH are inhibited and HIF-1α induces gene transcription, neoangiogenesis, tumor growth, and progression, as well as lack of responsiveness to RAI and chemotherapy [23,115,208].