Paroxysmal nocturnal hemoglobinuria terminating in TdT-positive acute leukemia

A case of paroxysmal nocturnal hemoglobinuria (PNH) which developed terminal transferase (TdT)-positive leukemia 5 years after the diagnosis of PNH was studied. Most of the leukemic cells were suggestively lymphoid by cytochemistry and electron microscopy, and TdT-positive by immunofluorescence studies. The development of acute lymphoblastic leukemia during the course of PNH suggests that in PNH the clonal abnormality may involve lymphoid cells as well as myeloid cells, thus raising the possibility of the disease being a disorder of the pluripotential stem cell.