ESR1 and breast cancer: Glycolytic flux is regulated at the level of phosphofructokinase-1 (PFK1) through the inducible enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), which is transcriptionally regulated by estrogen receptor signaling and has been shown to promote glycolysis and proliferation in ER<sup>+</sup> breast cancer cells.