Delayed Effect of Thorotrast Deposition in Humans: Carcinogenesis and Suppression of the Reticuloendothelial System

Abstract

Thorotrast is a colloidal solution containing 20% thorium (²³²Th), and used to be used primarily in diagnostic radiology for visualization. Once thorotrast is infused into the body, it is not eliminated easily. Over 90% of thorotrast forms deposits. It emits α-rays, and thorotrast-injected patients are semipermanently irradiated from α-particles deposited in the body. Thorotrast gives rise to malignant tumors by delayed effect of deposition, and especially liver cancer is highly associated with thorotrastosis. Deposition of thorotrast as an exogenous substance inhibits phagocytosis by suppressing the reticuloendothelial system (RES) as well and bringing about a Shwartzman preparatory state (preshock state) in patients. A majority of thorotrast-injected patients died abruptly. This short natural history of thorotrastosis is thought to have some relation to RES suppression by long-term thorotrast deposition resulting in vulnerability to shock and infection.