Radiation treatment of patients with primary pediatric malignancies: Risk of developing thyroid cancer as a secondary malignancy

Background: The aim of this study was to estimate the risk of thyroid cancer as a secondary malignancy after radiation treatment of primary pediatric malignancies. Methods: Using the Surveillance, Epidemiology, and End Results database, we identified 7,670 patients from 1973 to 1988 with primary pediatric malignancies. The relative risk of thyroid cancer in irradiated patients was calculated using the Poisson regression model, and the Cox proportional hazards regression model was used for survival rates. Results: The relative risk (RR) of thyroid cancer for children who received radiation was 2.22 (95% confidence interval [CI], 1.15-4.29). It was highest for central nervous system cancer (RR = 4.47) and lowest for those with leukemia (RR = 1.75). Mortality was significantly reduced for patients who received radiation as children; the hazard ratio was.80 (95% CI,.75-.86). Conclusions: Radiation for pediatric malignancies increases the risk of developing thyroid cancer as a secondary malignancy; however, these patients had localized disease and lower 20-year mortality.