Abstract
In 2012, a social issue arose concerning a high incidence of cholangiocarcinoma (bile duct cancer) among printing workers. The cause was prolonged exposure to high concentrations of 1,2-dichloropropane that was included in the ink cleaning agent. Until then, it was not known that this substance could cause cancer in humans. The author was involved in this incident from the beginning. This article describes the course from the start of the investigation to the recognition of cholangiocarcinoma as an occupational disease. Furthermore, the article presents the pathological characteristics of occupational cholangiocarcinoma, as well as epidemiological analysis results.