There are M1, M2, L and R isoforms of PK in mammalian cells: the M1 isoform (PKM1) is expressed in many differentiated tissues (skeletal muscle, heart and brain), PKM2 is expressed during embryonic development or over expressed in tumour tissues, PKL and PKR are expressed in liver and erythrocytes, respectively.12–14. The gene discussed is PKM; the disease is neoplasm.