HIF1A and neoplasm: Angiogenesis is an essential mechanism for tumor growth and maintenance, which may occur in response to environmental cues such as hypoxia stabilizing the transcription factor Hif-1α, that in turn activates the expression of angiogenic genes like Vegf-a. Levels of the Hif-1α mRNA were not different between LL and LD tumors, which can be explained by its relatively short-lived mRNA [54], or the oscillating O2 tumor levels (over the course of hours and days), which induce periodic fluctuations of tumor Hif-1α expression [55].