Objectives: We conducted a retrospective cohort study to examine the risk of bile duct cancer among current and former workers in the offset color proof printing department at a printing company in Osaka, Japan. Methods: Standardized incidence ratios (SIRs) between January 1, 1985, and December 31, 2012, were estimated for the cumulative years of exposure to two chemicals, dichloromethane (DCM) and 1,2-dichloropropane (1,2-DCP), using the national incidence level as a reference. In addition, we examined risk patterns by the calendar year in which observation started. Results: Among 106 workers with a total of 1,452.4 person-years of exposure, 17 bile duct cancer cases were observed, resulting in an estimated overall SIR of 1,132.5 (95% confidence interval (CI): 659.7–1,813.2). The SIR was 1,319.9 (95% CI: 658.9–2,361.7) for those who were exposed to both DCM and 1,2-DCP, and it was 1,002.8 (95% CI: 368.0–2,182.8) for those exposed to 1,2-DCP only. SIRs tended to increase according to years of exposure to 1,2-DCP but not DCM when a 5-year lag time was assumed. The SIRs were higher for the cohorts in which observation started in 1993–2000, particularly in cohorts in which it started in 1996–1999, compared with those in which it started before or after 1993–2000. Conclusions: We observed an extraordinarily high risk of bile duct cancer among the offset color proof printing workers. Elevated risk may be related to cumulative exposure to 1,2-DCP, but there remains some possibility that a portion of the risk is due to other unidentified substances.(J Occup Health 2015; 57: 230–236)

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