Estimated absorbed dose in tissues and radiation effects in Japanese Thorotrast patients

Multiple, unique, and common p53 mutations in a thorotrast recipient with four primary cancers

Four primary cancers found at autopsy of a patient who received the thorium-based contrast agent Thorotrast 50 years ago and who was healthy up until a few months before his death from liver failure were analyzed for p53 mutations. The data suggest that the chronic alpha-irradiation may be a large causative factor. Multiple mutations were found in all the cancer tissues: two foci of a cholangiocellular carcinoma, a tubular adenocarcinoma of the stomach, a squamous cell carcinoma of the lung, and an adenocarcinoma of Vater's ampulla. The total number of point mutations detected were 13. Moreover, homozygous aberrations were detected in a large area of normal small intestine and noncancer liver tissues suggesting that nontumor cells which harbored p53 abnormalities gained a survival advantage and clonally expanded.

Lung cancers associated with thorotrast exposure: high incidence of small-cell carcinoma and implications for estimation of radon risk

The widely accepted concept that the alpha-emitting radionuclide radon (222Rn, 220Rn) induces lung cancers in humans has been based on the excess of lung tumours observed in underground miners extracting uranium or other substances. However, this poses the important question of whether radon is the only carcinogenic factor because such miners are also heavily exposed to mine dusts including silicates, diesel exhaust, etc. in their working environment. Patients to whom Thorotrast was administered continuously exhale radon (220Rn) derived from 232Th deposits in the body and therefore provide a good model for lung carcinogenesis by radon without concomitant dust exposure. We therefore investigated lung-cancer incidence in our epidemiological follow-up series, analysing the histological types of 11 lung cancers which were found among 359 Thorotrast autopsy cases and measuring radioactivity in the breath of living Thorotrast patients. The study revealed that, while the proportion of small-cell lung cancers considered to be related to alpha-particles was significantly increased, the overall lung cancer incidence was not significantly higher than in controls, in spite of the high level of 220Rn in the patients' breath. This result suggests that radon in the lung does induce cancers (particularly small-cell carcinomas) but that the induction rate is not as high as expected from risk factors associated with mining. Thus, excess lung cancers among the miners might be related to the combined effects of exposure to radon and mine dusts, and not solely to radon.