STAT3 and neoplasm: While PKM1 forms a tetrameric complex that cannot enter the nucleus, PKM2 forms dimers that, upon nuclear translocation, acquire protein kinase activity and support the tumor-promoting transcription factors HIF1α, STAT3, and β-catenin (Figure 5A; Alves-Filho and Pålsson-McDermott, 2016; Luo et al., 2011; Yang et al., 2011).