HIF1A and breast cancer: Stromal cells such as tumor associated fibroblasts may induce TGFβ signaling in breast cancer cells to hyperactivate the peroxisome proliferator activated receptor alpha (PPARα)/HIF1α axis, which regulates multiple survival and self-renewal genes including CAIX, apolipoprotein E (APoE), snail family transcriptional repressor 2 (Slug) and interleukin 6 (IL6) to promote cancer stemness.