Objective While patients with gastrointestinal cancer are at increased risk of cholangitis, it is less clear whether cholangitis is also a marker for occult gastrointestinal cancer. If an undiagnosed cancer obstructs the bile duct system and causes cholangitis, the short-term risk of cancer will appear increased. However, an increased long-term risk of cancer may originate from chronic inflammatory processes. We assessed the risk of a gastrointestinal cancer diagnosis subsequent to a cholangitis diagnosis during a 17-year period in Denmark.

Design We conducted a nationwide population-based cohort study by linking Danish medical registries during 1994–2010. We quantified the excess risk of cancer in cholangitis patients using relative (standardised incidence ratio; SIR) and absolute (excess absolute risk per 1000 person-years at risk; EAR) risk calculations.

Results 4333 patients with cholangitis (including 178 with primary sclerosing cholangitis) were followed for 17 222 person-years. During the follow-up period, 477 gastrointestinal cancers occurred versus 59 expected, corresponding to a SIR of 8.12 (95% CI 7.41 to 8.88). Risk was increased mainly for cancer in the small intestine (SIR 18.2; 95% CI 8.69 to 33.4), liver (SIR 16.3; 95% CI 11.6 to 22.2), gallbladder and biliary tract (SIR 70.9; 95% CI 59.0 to 84.4) and pancreas (SIR 31.7; 95% CI 27.8 to 36.0). During the first 6 months of follow-up, 314 patients were diagnosed with gastrointestinal cancer, corresponding to a SIR of 49.8 (95% CI 44.4 to 55.6) and an EAR of 175.

Conclusions Cholangitis is a marker of occult gastrointestinal cancer.