Leukemia among atomic bomb survivors

The depression of bone marrow induced by single dose of whole body irradiation was the most critical damage leading to death in the atomic bombings. The radiation-related hematologic disorders in atomic bomb survivors may be leukemia, multiple myeloma, malignant lymphoma, a plastic anemia, polycythemia vera and myelofibrosis. The air dose values in Hiroshima at 1.5 km from the hypocenter was about 32 rad, consisting 22 rad gamma and 10 rad neutrons. At 2 km, this was about 2.5 rad; 2 rad gamma and 0.5 rad neutrons. There is strong correlation between increasing leukemia risk and decreasing distance from the center of explosion. Most patients with chronic granulocytic leukemia (CGL) had high leukocyte counts, splenomegaly, high percentage of immature granulocytes, low neutrophil alkaline phosphatase (N-AP) activity and Philadelphia (Ph1) chromosome in the bone marrow. Basophillia was confirmed in the early phase of leukemia in 15 of 16 patients, on whom the classification of the peripheral leukocytes was examined prior to the clinical onset of CGL. Ph1 chromosome seemed to be a marker of preleukemic state, and is not a leukemic process itself. The time needed for a large amount of the cell mass (1011/liter) of Ph1-positive cells to accumulate was calculated to be about 3.2 years, based on cell generation time. Development of CGL can be divided into 3 stages: proliferative stage of 6.3 years, preclinical stage of 19 months and advanced stage of 3 years. (Yamashita, S.)