HIF1A and breast cancer: In breast cancer, intratumorally low oxygen levels (hypoxia) are associated with aggressive tumor behavior, metastasis, and treatment resistance.3, 4, 5 The transcription factor hypoxia-inducible factor 1α (HIF-1α), a major regulator of cellular adaptation to hypoxia, is highly expressed in several cancer types and is associated with poor breast cancer prognosis.6