The aetiology of cancer of the extrahepatic bile duct is unknown. Gallstones have been proposed to be a risk factor on the basis of ecological and epidemiological evidence. As gallstones are formed in the gallbladder, the occurrence of extrahepatic bileduct cancer in patients after cholecystectomy is of interest. All patients (62 734) who had had a cholecystectomy during 1965–1983 within the Uppsala Health Care Region, Sweden, were followed up to the end of 1987. Excluding the first year of follow‐up, 23 cancers of the extrahepatic bileduct occurred vs 26.3 expected for a standardised incidence ratio (SIR) of 0.88 (95% confidence interval [CI] 0.56–1.31). Ten years or more after operation there was a greater reduction of risk (SIR=0.27; 95% CI 0.06–0.80). Similar patterns were observed for men and women, and among patients who had undergone cholecystectomy only compared with those who had had their common bileducts explored. To assess surveillance bias the incidence of primary liver cancer was also analysed: SIR=1.15; 95% CI 0.91–1.44 overall, and 10 years or more after cholecystectomy SIR=0.98; 95% CI 0.66–1.40. This study shows a reduced risk of extrahepatic bileduct cancer 10 or more years after cholecystectomy, indicating that gallstones may be a cause of cancer.
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