Second malignancies in thyroid cancer patients: a population-based survey of 3658 cases from Norway.

In a population-based survey of 3658 thyroid cancer patients diagnosed in Norway during 1955-85, a total of 200 cases of second malignancies were observed (30,414 person-years, mean follow-up 8.4 years). Male patients had a significantly increased incidence of urogenital cancer [standardised incidence ratio (SIR) = 1.96, 95% confidence interval (CI) 1.4-2.7], including cancer of the testis (SIR = 11.8, 95% CI 3.2-30.1) and urinary bladder (SIR = 3.0, 95% CI 1.5-5.2). The occurrence of malignant melanoma was also increased among males (SIR = 4.2, 95% CI 1.4-9.7). This apparent association with urogenital cancers among males at the present time cannot be explained, although increased surveillance as well as specific aetiological factors should be considered.