CANCER INCIDENCE AND MORTALITY AFTER I-131 THERAPY FOR HYPERTHYROIDISM

Cancer risk teas studied In 10,552 Swedish hyperthyroid patients treated with I-131 between 1950 and 1975. Patients were followed for an average of 15 years (range 1-35 years) and were matched with the Swedish Cancer Register (SCR) and the Swedish Cause of Death Register (SCDR). The overall standardized incidence ratio (SIR) was 1.06 [95% confidence interval (CI) = 1.01-1.11], and the overall standardized mortality ratio (SMR) was 1.09 (95% CI = 1.03-1.16). The stomach was the only site for which cancer risk increased over time (p < 0.05) and with increasing activity of I-131 administered (p = not significant). No Increased incidence of leukemia was found, which adds further support to the view that a radiation dose delivered gradually over time is less carcinogenic than the same total close received over a short time. A possible excess owing to radiation teas suggested only far stomach cancer.