PKM and neoplasm: Hypoxia-induced alternative pre-mRNA splicing influence on tumour metabolic reprogramming takes its initial cues from physiological metabolic reprogramming under anaerobic conditions, which initiates with HIF1α stabilization and HIF1 promotion of glycolysis-promoting alternative pyruvate kinase PKM2 splice variant isoform expression, at the expense of the oxidative phosphorylation-promoting PKM1 isoform, resulting in a metabolic shift to glycolysis.