<綜説>発癌と免疫 (1) 放射性発癌

Abstract

a) Clinical approach to tumor induction by irradiation : Many clinical cases of cancer or leukemia thought to be induced by irradiation were published in the past, but only studies standing with statistical analysis of cases were reliable, as spontaneous occurrence had to be considered. According to March (1944), Henshaw and Hawkins (1944) and Ulrich (1946), leukemias occurred more frequently in radiologists than in other physicians. The Japanese Committee on Biological Influences of The Atomic Bomb (1953, 1956) also reported considerable occurrence of leukemias in Hiroshima and Nagasaki. b) Experimental approach : The most comprehensive and attractive experimental studies on X-ray induction of thymoma in C57BL mice were achieved by Kaplan and his associates (1947-1958). The mice were most sensitive to fractional irradiation at age of one month and produced tumors in almost one hundred per cent of those irradiated. Inhibitory effect on the tumor induction by bone marrow protection against irradiation or transplantation of isologous cells after irradiation were demonstrable. Tumors were also induced in the thymus transplanted in thymectomized and irradiated hybrids and were thought not to be parental in cellular origin, but to be autologous. This means that the tumors came up in the process not of injury, but of recovery. c) Immunological consideration of tumor induction : It is well known that irradiation induces serious damage especially to lymphoid tissues which are considered to be necessary for tumor immunity. This suggests that suppressed antibody formation in irradiated animals may permit further growth of transformed cells, if induced by or after irradiation, containing newly-occurring tumor antigens.