LETTERS TO THE EDITOR

abnormalities observed may be responsible for the leukemias noted. However, this is not necessarilyso. The atomic-bomb survivors suffered iota/-body irradiation, which included hemopoietic stem ce//s in the bone marrow. In light of present knowledge, it is almost certain that the leukemias arose from radiation damage to stem cells (5), and that abnormalities seen in circulating lymphocytes are simply “flags―to alert one to the fact that stem cells were damaged as well. Mature lymphocytes may circulate without di viding for a decade or more (8); it is probable that most of the abnormal cells had been circulating without division since the bomb, as many that are forced to divide (e.g., with phytohem agglutinin) die due to severe chromosomal imbalances after mi tosis. To quote Yunis (5), “Thegeneral finding of shared chro mosomal defects among certain leukemias and lymphomas implies that primary chromosomal defects in neoplasias affect stem cell