PFKFB3 and cancer: Given the recent reports that PFKFB4 functions as a dominant bisphosphatase in cancer cells [15], we were surprised to find that recombinant human PFKFB4 had significant kinase activity that was ~15% that of the PFKFB3 family member whose kinase domain has previously been established to set the intracellular concentration of F2,6BP in multiple cell lines (PFKFB4 kinase Vmax = 5.06±0.2 mU/mg, PFKFB3 kinase Vmax= 38.4 ±2.3 mU/mg) (Fig. 2A) [18, 20, 21].