PKM and cancer: Much evidence indicates that PKM1, another isoform of Pyruvate kinase muscle (PKM) gene, is expressed in normal differentiated tissues, whereas PKM2 is expressed in proliferating and cancer cells, heterogeneous nuclear ribonucleoprotein (hnRNP) family can regulate the alternative splicing to switch their PKM isoform from PKM1 to PKM2 during tumor development [45].