HIF1A and breast carcinoma: Compared to the chemical-induced cancer, tumor formation was also followed in the transgenic PyMT breast cancer model by crossing C57BL/6J conditional Hif-1αLysM−/−, Hif-2αLysM−/−, and Hif-1α/2αLysM−/− mice with mice expressing the PyMT oncoprotein.