Aim
The purpose of this study was to assess the long-term risk of biliary cancer in patients diagnosed with choledochal malformations (CMs).

Methods
The patient population was collected from the Helsinki University Hospital registers including all consecutive patients from 1987 to 2020. This data were complemented with the population-based register data from the Finnish Register of Congenital Malformations (FRM) and the Finnish Care Register for Health Care (1987–2020). Patient population was cross-linked with data from the Finnish Cancer Register data and the Cause-of-Death Register.

Results
There were 209 patients with CM (142 females and 67 males). Most patients (n = 110, 53%) underwent biliary diversion surgery, 18 patients (8.6%) were treated endoscopically, and 57 patients (27%) were managed with observation only. Three patients (1.4%) were diagnosed with biliary cancer at a mean age of 60.3 years, and all of them died of their disease at a mean age of 65.4 years. Cholangitis was diagnosed in 33 patients (16%). Risk of inflammatory bowel diseases (IBDs) appeared higher in CM patients than in general Finnish population as IBD was diagnosed in 10 patients (4.8%) with relative risk (RR) of 4.9 (95% confidence interval [CI] 2.7–9.0).

Conclusions
CM seemed to be associated with an increased risk of biliary cancer although the prevalence was lower than in previous reports.