Leukemia in women following radiotherapy for cervical cancer: ten-year follow-up of an international study.

An international collaborative study of 31,219 women treated for cervical cancer from 30 radiotherapy centers in nine countries was conducted. Patients were followed clinically and with blood studies between 1960 and 1970, and 148,000 woman-years (WY) were accumulated. Among 28,490 women treated with either intercavitary radium, external radiation, or both, 134,000 WY were accumulated and 13 cases of leukemia were observed. On the basis of general population rates, 15.5 cases were expected [relative risk (RR) = 0.8; 95% confidence limits (CL) = 0.4-1.4]. A twofold risk could thus be excluded, but a 1.4-fold risk remained possible. In absolute terms, risks larger than 0.1 leukemia cases per 10(6) WY-rad could be excluded. Among 2,729 cervical cancer patients not irradiated but similarly evaluated, 14,000 WY were accumulated and 2 cases of leukemia were observed as compared with 1.0 expected. In the interval 4-8 years after exposure, the period in which any leukemogenic effect might be most apparent, 7 cases of leukemia were observed among exposed patients as compared with 5.4 expected (RR - 1.3; 95% CL = 0.5-2.7). The absence of an increased leukemia risk suggested that the radiation regimens used to treat cervical cancer are not so effective in inducing leukemia as are other radiation exposures that have been studied.