PKM and neoplasm: There are at least 12 known functionally separate isoforms of pyruvate kinase (PKM), reported as being produced by alternative splicing, with switching between the major isoforms from M1 (PKM1) to M2 (PKM2) implicated in tumor cell growth, with the latter being a central driver of aerobic glycolysis in tumors and other highly proliferating cells (52).