HIF1A and neoplasm: Bone volume and trabecular number were significantly decreased in Hif1α−/− PyMT+ mice, with an accompanying increase in trabecular spacing (Fig. 2a–d), but bone volume was unaltered with Hif1α deletion in PyMT− mice, suggesting that the reduction in bone volume observed in Hif1α−/− PyMT+ mice was due to tumor-induced osteolysis.