Cancer risk following exposure to Thorotrast: overview in relation to a case report

Radioactive measurements and histopathologic findings are described in a patient administered Thorotrast, a radiographic contrast agent, 36 y prior to death and compared with cancer risks noted in epidemiologic studies. This person [designated as U.S. Uranium Registry (USUR) Case 1001] had prearranged for donation of her body to the USUR and the National Cancer Institute for study. Elevated levels of radioactivity were noted in those organs in which excess cancers have been reported in epidemiologic surveys of Thorotrast-exposed subjects. Hepatic tissue in USUR Case 1001 was estimated to have received an average lifetime absorbed dose of 16.2 Gy, based on radiochemical analyses, consistent with the high risks for liver tumors reported in all studied populations. Thorotrast was present throughout the bone marrow of USUR Case 1001, who died secondary to complications of refractory anemia with excess blasts (RAEB). Elevated risks for acute myeloid leukemia have been noted in Thorotrast patients, and more recently, cases of RAEB and RAEB in transformation have been reported. The thorium decay series includes the bone-seeking radionuclides 224Ra and 228Ra, which have been associated with high risks for osteosarcomas, although the association between Thorotrast and bone cancer is not as convincing. The skeleton of USUR Case 1001, however, contained significant levels of radioactivity. Other tissues evaluated in USUR Case 1001 included lung, eye, kidney, and breast, which did not contain elevated levels of radioactivity.