Female residents of 13 counties of Western Washington, in whom papillary, follicular, or mixed papillary-
follicular thyroid carcinomas had been diagnosed between 1974 and 1979 were interviewed regarding their medical and reproductive histories and past exposure to
radiation treatments. For comparison, a random sample of women from the same population was interviewed. Women who had received
radiation treatments to the head or neck prior to 5 years before interview were 16.5 times (95% confidence interval = 8.1-33.5) more likely than unexposed women to develop
cancer. The relative risk (RR) was highest for papillary
cancer (19.4) but also was elevated substantially for follicular and mixed papillary-follicular
tumors. Women first irradiated at age 19 years or younger had a much higher RR than did women irradiated at age 20 or older. Regardless of prior radiation exposure, women who ever had had a
goiter were at increased risk of developing
thyroid cancer. Women who had ever developed a
goiter had 17 times the risk of developing follicular
cancer and almost 7 times the risk of developing papillary
cancer as compared with women who never had had a
goiter. Risk of
thyroid cancer was elevated even among women who had had a history of
goiter many years prior to diagnosis. A history of
thyroid nodules was also a risk factor for papillary and mixed
thyroid cancer. Neither a history of
hypothyroidism nor
hyperthyroidism was found to increase the risk of
thyroid cancer.