Experimental manipulation of preleukemic change in whole-body irradiated RFM/Up mice (38542)

Radiation which induces leukemogenesis in the unirradiated mouse, inhibits leukemogenesis if given again to the previously irradiated, but not yet leukemic mouse. The objective of this experiment was to identiry nonmalignant late radiation in jury in the bone marrow, the modification of which by a second exposure may account for postponement of radiogenic leukemia. To this end, leukemogenically irradiated RFM/Up mice were reirradiated under conditions known to bring about postponement of the leukemias due to the first radiation exposure. Quantitative analysis of the femoral pone marrow of these mice shows that leukemia incidence is positively correlated with the number of immature myeloid cells, and negatively correlated with the percentage of the mature myeloid cells in the entire myeloid series. The implications of this for the understanding of preleukemic change are discussed.