LEUKEMIA AFTER IRRADIATION FOR ENDOMETRIAL CANCER IN ONTARIO

Background. In human studies, the risk of leukemia after ionizing radi ation has been found to be increased more often than for any other can cer. It is useful to study patients with cancer treated with radiation because exposure can be measured accurately, follow-up may be long, a nd often a comparable and sizable nonexposed group exists. Women with endometrial cancer represent an excellent population for study because they meet these Developed Leukemia After Endometrial. Methods, A popu lation-based matched case-control study, nested among all patients wit h endometrial cancer diagnosed in Ontario, was undertaken to describe the relationship between radiation therapy and leukemia risk, Among 13 ,843 subjects treated from 1964 to 1987 who survived at least 1 year, 47 confirmed cases of leukemia were identified. Four control subjects were matched to each patient based on age, calendar year of diagnosis, and length of survival free of a second neoplasm. Medical records wer e abstracted, and radiation dose administered to active bone marrow wa s determined by dosimetry. Results. An elevated risk of all leukemias other than chronic lymphocytic leukemia was observed, but only within the first 10 years after endometrial cancer treatment (odds ratio 12.0 ; 90% confidence interval 2.8-52.1). There was insufficient statistica l evidence that risk was influenced by dose or type of radiation thera py, Nor was there any evidence that risk was influenced by age at endo metrial cancer diagnosis or by calendar period at diagnosis. Conclusio ns. There is an increased risk of leukemia associated with radiation t herapy for patients with endometrial cancer, but only within the first 10 years after treatment.