MYELOID LEUKEMIA IN THE MOUSE.

Abstract

The incidence of myeloid leukemia is elevated in RF mice acutely exposed early in adult life to 50 to 400 rads of whole-body x radiation. The relation between incidence and dose is complex, the yield of leukemias declining as the dose is increased above an optimal level. X rays and gamma rays are less leukemogenic when administered daily at low dose rates than when administered in one or two large exposures at high dose rates. The leukemogenic effectiveness of fast neutrons depends on the neutron energy but appears generally comparable to that of x rays. In contrast, however, the effectiveness of fast neutrons shows no detectable reduction with decrease in dose rate. A given dose in air to part of the body is less leukemogenic than the same dose in air to the whole body, but quantitative data on the relative importance of the integral dose and of the volume and region of the body irradiated are not available. The average induction period of leukemia after wholebody x irradiation is 6 to 12 months depending on the dose, although the earliest radiogenic leukemias become detectable within two months. In contrast to the relatively long average latency of leukemia induced bymore » irradiation, the neoplasm appears in a significant number of nonirradiated recipients within one month after injection of cellfree filtrates of leukemic tissue. The age-specific death rate from the disease is biphasic. Radiation markedly advances the onset of the early peak, which occurs in controls between the fifteenth and eighteenth months of life. Radiation affects the late peak (occurring at 22 to 24 months) relatively less, if at all. The results of these studies suggest that the leukemic transformation induced by radiation evolves through multiple changes rather than through a single, one-hit type of alteration in a host cell or in the virus-host relation. (auth)« less