To elucidate the role of HIF in macrophages during carcinogenesis, we analyzed tumor formation in wild type (wt) mice or mice carrying a myeloid-specific knockout of Hif-1α, Hif-2α, and Hif-1α/2α in the transgenic PyMT breast cancer model as well as chemical carcinogenesis, induced by subcutaneous injection of MCA. This evidence concerns the gene EPAS1 and neoplasm.