HIF1A and neoplasm: In this spontaneous model, mammary tumors were first palpable around 8 weeks of age and reached end point (any tumor reaching 1 cm in diameter) around 20 weeks of age for the Hif1αf/f PyMT+ mice, while the Hif1α−/− PyMT+ mice took significantly longer to reach end point, at an average of 23 weeks of age (Fig. 1b, c).