A Comparative Study of the Leukemogenic Effects of Strontium-90 and X-Rays in Mice

Summary

The leukemogenicity of ⁹⁰Sr was studied in comparison with that of fractionated total-body X-irradiation in the low leukemia ICR/JCL strain of mice. Fractionated total-body X-irradiation of 680 R yielded leukemia in 77.3% of mice, of which all but one were of thymic origin. A single intraperitoneal dose of 1.0 μCi/g of body weight also had a high leukemogenic effect (61.8%). The ⁹⁰Sr-induced leukemias were cytologically of lymphoblastic, reticulum cell, or stem cell type, not of thymic origin. No myeloid leukemia occurred in these mice. Thymectomy inhibited the leukemogenic effect of total-body X-irradiation as reported by others, while the induction of leukemia by ⁹⁰Sr was not inhibited by thymectomy. It is postulated that X-irradiation produces progenitors of leukemic cells in bone marrow or spleen, and these cells migrate into the injured thymus where they proliferate, while the similar progenitor cells can be produced in bone marrow by direct effects of ⁹⁰Sr. As grafted lymphomas they migrate into lymphoid and other tissues but not preferentially into the thymus. Three cases of leukemia induced by ⁹⁰Sr and 2 cases by X-rays were transmitted by presumably cell-free extracts. It is suggested, therefore, that a viral factor may take part in the leukemia induction by ⁹⁰Sr as it does in induction of leukemia by X-rays.