PKM and cancer: The embryonic pyruvate kinase isoform, PKM2, is almost universally re-expressed in cancer and is the predominant isoform of pyruvate kinase expressed in normal hematopoietic and leukemic cells.11,22 Interestingly, we observed that PKM2 was expressed at very high levels within CLL lymph nodes, where it was not confined to PCs, whereas PKM1 was expressed at low levels.