HIF1A and neoplasm: Indeed, ATRA induces the expression of HIF-1α (Hypoxia-Inducible Factor 1-alpha) and VEGF in certain solid tumors and the ATRA/HIF-1α/VEGF pathway has been reported to promote tumor angiogenesis in HUVEC co-cultures and xenografts of the MCF-7 breast cancer cell line [88].