DCM and 1,2-DCP were used to remove ink from
the ink rollers. Both chemicals were used between
April 1991 and February 1996, and subsequently
only 1,2-DCP was used until October 2006 (Fig. 1).
Cumulative exposure years were calculated for each
chemical on an individual basis from the date of
beginning employment at the company or the date of
initial use of the chemical, whichever occurred latest,
until the date of retirement or the date of bile duct
cancer diagnosis, whichever occurred first. Personyears
were accumulated throughout the entire cohort
according to years of exposure