Thyroid cancer risks of irradiation: data from Nagasaki survivors

The Radiation Effects Research Foundation, previously called the Atomic Bomb Casualty Commission, examined about 2,500 men and women exposed to the Nagasaki atomic bomb in August 1945 between 1984 and 1987 then followed them for a mean of 13 years. They included 68 people with ultrasound-detected solid thyroid nodules, of which 31 were diagnosed as benign by cytological and histological examination, and 121 people with thyroid cysts.Thyroid cancer was subsequently diagnosed in 9.7% of those with 'benign' nodules, compared to 0.8% of those with cysts and 0.3% of those with normal thyroids at baseline. The hazard ratio associated with benign cysts was 23.7. Cancer risk was not associated with sex, age, TSH level, thyroglobulin level, radiation dose, baseline nodule volume or the change in nodule volume over time."This result will contribute to clinical guidelines for the management of thyroid nodules in individuals irradiated by radiation therapy, nuclear plant accidents or nuclear weapons," the researchers stated. "We recommend at least biennial follow-up for irradiated people with thyroid nodules even if they are diagnosed as benign."Aspiration biopsy always had a risk of generating a false-negative result, which might have explained some of the cases of subsequent malignancy. However, it was more likely that new malignant foci were associated with pre-existing benign disease, or that occult malignant foci were already present at the time of biopsy. It was widely known that radiation exposure increased both thyroid nodules and thyroid cancer, but there had been considerable uncertainty about the threat posed by apparently benign nodules. Previous studies had generally relied on retrospective data from cases and controls, and were therefore less robust. Reference...