A retrospective cohort morbidity study based on standardized incidence ratios (SIRs) was conducted to investigate the possible association between exposure to chlorinated organic
solvents and various types of
cancers in an electronics factory. The cohort of the exposed group was retrieved from the Bureau of Labor Insurance (BLI) computer database records dating from 1978 through December 31, 1997. Person-year accumulation began on the date of entry to the cohort, or January 1, 1979 (whichever came later), and ended on the closing date of the study (December 31, 1997), if alive without contracting any type of
cancers, or the date of death, or the date of the
cancer diagnosis. Vital status and cases of
cancer of study subjects were determined from January 1, 1979 to December 31, 1997 by linking cohort data with the National
Cancer Registry Database. The
cancer incidence of the general population was used for comparison. After adjustment for age and calendar year, only SIR for
breast cancer in the exposed female employees were significantly elevated when compared with the Taiwanese general population, based on the entire cohort without exclusion. The SIR of female
breast cancer also showed a significant trend of period effect, but no significant dose-response relationship on duration of employment. Although the total
cancer as well as the
cancer for trachea, bronchus and lung for the entire female cohort was not significantly elevated, trend analysis by calendar-year interval suggested an upward trend. However, when duration of employment or latency was taken into consideration, no significantly elevated SIR was found for any type of
cancer in either male or female exposed workers. In particular, the risk of female
breast cancer was not indicated to be increased. No significant dose-response relationship on duration of employment and secular trend was found for the above-mentioned
cancers. This study provides no evidence that exposure to chlorinated organic
solvents at the electronics factory was associated with elevated human
cancers. Dominant short-term employees may bias the
cancer risk toward false positive.