Comparison of second cancer risks from brachytherapy and external beam therapy after uterine corpus cancer.

BACKGROUND Adjuvant radiotherapy is common for uterine corpus cancer patients, yet the long-term carcinogenic effects of different types of radiotherapy have not been studied adequately. METHODS Second primary cancer risks were quantified in a cohort of 60,949 individuals surviving > or = 1 year of uterine corpus cancer diagnosed from 1973 to 2003 in Surveillance, Epidemiology and End Results Program cancer registries. Incidence rate ratios (IRR) were estimated by comparing patients treated with surgery plus various types of radiotherapy with patients receiving surgery only. RESULTS The IRRs of a second cancer were increased among irradiated patients compared with patients having surgery only [combination radiotherapy, IRR = 1.26; 95% confidence interval (CI), 1.16-1.36; external beam therapy, IRR = 1.15; 95% CI CI, 1.08-1.22; brachytherapy, IRR = 1.07; 95% CI, 1.00-1.16]. IRRs were highest for heavily irradiated sites (that is colon, rectum, and bladder) and for leukemia following any external beam therapy, with the largest risks for solid cancers among 10-year survivors. Any external beam therapy had a 44% higher cancer risk at heavily irradiated sites than brachytherapy when the two treatments were directly compared (5-year survivors: IRR = 1.44; 95% CI, 1.19-1.75). We estimated that of 2,012 solid cancers developing > or = 5 years after irradiation, 213 (11%) could be explained by radiotherapy. CONCLUSIONS Radiotherapy for uterine cancer increases the risk of leukemia and second solid cancers at sites in close proximity to the uterus, emphasizing the need for continued long-term surveillance for new malignancies. The overall risk of a second cancer was lower following brachytherapy compared with any external beam radiotherapy.