Reproductive factors and risk of biliary tract cancer in a population-based study

Background. The strong female predominance of biliary tract cancer (BTC) may be related to reproductive factors. We aimed to clarify whether parity or age at first birth influence the risk of BTC. Methods. This was a population-based, case-control study including Swedish female and male cases of cancer of the gallbladder (GBC), extra hepatic bile ducts (EHCC), or the ampulla of Vater (AVC) between 1960 and 2008. For each case, 10 age-and sex-matched controls were randomly selected. Conditional logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CIs), adjusted for potential confounders. Results. In total, 1169 cases of GBC, 432 cases of EHCC and 295 cases of AVC were included. Multi-and nulliparous women and men had an increased risk of all tumor locations in the biliary tract compared to uniparous women and men, respectively. Whereas higher age at first birth was associated with a decreased risk of GBC in women, no such association was found in men. There were no clear differences in the risk of EHCC and AVC between women and men. Conclusion. Sex hormones may play a role in the etiology of GBC. The associations between reproductive factors and EHCC and AVC are similar in women and men, which do not support the sex hormone hypothesis.