Mortality in the Portuguese Thorotrast study

The Portuguese Thorotrast study cohort consists of a group of patients who received Thorotrast for diagnostic reasons between 1929 and 1956, and a gro up of similar patients who were given nonradioactive contrast agents, The c ohort members were identified from medical records that contained informati on on reasons for the radiological investigation, type of procedure employe d, and name and dose of the contrast medium used. This cohort was assembled in 1961, but its follow-up was interrupted in 1976, We have now reactivate d this cohort and extended its follow-up through the end of 1996, Similar m ethods were used to follow up and ascertain cause of death for the Thorotra st-exposed and unexposed subjects. A total of 1931 patients who received Th orotrast systemically and 2258 unexposed subjects were initially identified from medical records, We were able to successfully follow up 58.6% (1131) of the Thorotrast patients and 45.7% (1032) of the unexposed patients. By t he end of 1996, 92.2% of the Thorotrast patients and 75.2% of the unexposed patients were dead, Mortality from all causes was increased in the Thorotr ast patients compared to those who were not exposed. This excess in mortali ty increased with time since exposure, peaking 30 years after administratio n of Thorotrast. The rise in overall mortality was essentially due to neopl asms [relative risk (RR) adjusted for sex, age and period = 6.04, 95% CI = 4.42-8.26], nonmalignant liver disorders (RR = 5.67, 95% CI 3.13-10.3) and nonmalignant hematological conditions (RR = 14.2, 95% CI = 2.54-79.3). The increase in mortality from neoplasms was explained mainly by increases in t he risk of liver cancer (RR = 70.8, 95% CI = 19.9-251.3) and, to a much les ser extent, leukemia (RR = 15.2, 95% CI = 1.28-181.7). (C) 1999 by Radiatio n Research Society.