We estimated the risk of thyroid cancer among 9170 patients who had survived 2 or more years after the diagnosis of a cancer in childhood. As compared with the general population, patients had a 53-fold increased risk (95% confidence interval, 34–80). Risk increased significantly with time since treatment for the initial cancer (P = 0.03). Detailed treatment data were obtained for 23 cases and 89 matched controls from the childhood cancer cohort. Sixty-eight % of the thyroid cancers arose within the field of radiation. Radiation doses to the thyroid of > 200 cGy were associated with a 13-fold increased risk (95% confidence interval, 1.7–104). The risk of thyroid cancer rose with increasing dose (P < 0.001), but this was derived almost entirely from the increase from <200 to >200 cGy. The risk of thyroid cancer did not decrease, however, at radiation doses as high as 6000 cGy.
Supported in part by Public Health Service Contract N01CP-91049 from the Division of Cancer Etiology, National Cancer Institute.