PKM and cancer: Of these, PKL is found mainly in gluconeogenic tissues, especially the liver; PKR is found mainly in erythrocytes and hematopoietic tissues.PKM1 is highly expressed as a tetramer in cardiac, skeletal muscle, and brain tissues; PKM2 is expressed as a monomer, dimer, or tetramer in the lungs, spleen, kidneys, and testes [130–132]; in mature differentiated cells, PKM1 predominates, while PKM2 is highly expressed in cancer cells and embryos [133, 134].