Subsequent development of cholangiocarcinoma caused by exposure to 1,2-dichloropropane and/or dichloromethane in the printing company in Osaka, Japan.

After the report of 17 patients with occupational cholangiocarcinoma caused by long-term exposure to high concentrations of 1,2-dichloropropane and/or dichloromethane in a printing company in Osaka in 2014, additional five patients were diagnosed to have such cholangiocarcinoma. Cholangiocarcinoma was detected during regular health examination or follow-up for liver dysfunction in four of the five patients. Nearly all five patients presented with clinicopathological findings such as an elevated γ-glutamyl transpeptidase activity at the diagnosis, regional dilatation of intrahepatic bile ducts without tumor-induced obstruction, chronic bile duct injury, and precancerous/early cancerous lesions (biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct) at various sites of the bile duct. These findings were similar to those of the previous 17 patients. In total, cholangiocarcinoma developed in 22 of 95 workers exposed to 1,2-dichloropropane in the printing company. Of 22 patients with cholangiocarcinoma, 18 patients were members of 19 high exposure workers (≥1,500 ppm-years). These findings strengthen further the theory that 1,2-dichloropropane causes occupational cholangiocarcinoma. Regular health examination of workers exposed to 1,2-dichloropropane and/or dichloromethane is necessary to detect such cholangiocarcinoma because the potential of the carcinogenesis risk persists over the long term.