HIF1A and neoplasm: The mechanism behind the decreased bone volume in Hif1α−/− PyMT+ mice remains unclear; however, it is important to note that there was no difference in bone volume between Hif1αf/f and Hif1α−/− PyMT− mice, suggesting that the reduction in bone volume is not due to deletion of Hif1α in off-target cell lineages, but rather due to tumor-related factors.