PKM and colorectal cancer: In 5-fluorouracil (5-FU)-resistant colorectal cancer, suppression of PKM2 leads to upregulation of pyruvate kinase M1 (PKM1) and impairment of the pentose phosphate pathway (PPP), resulting in decreased nicotinamide adenine dinucleotide phosphate (NADPH) production and weakened antioxidant defenses.