In the POELH-II trial (Clinicaltrials.gov ID NCT05678218) patients with presumed resectable perihilar (pCCA), intrahepatic (iCCA) or mid-common bile duct (CBD) cholangiocarcinoma had the outcomes of their preoperative endoscopic ultrasound (EUS) registered. This EUS procedure was done systematically, targeting lymph nodes (LNs) with the aim to identify LN metastases preoperatively.

The goal of this follow-up observational cohort study (POELH-III) is to assess the yield of preoperative EUS, with an improved EUS approach. The EUS protocol as used in the POELH-II trial was improved based on preliminary results of the POELH-II trial. The main questions it aims to answer is:

- The number of patients precluded from surgical work-up due to positive regional or extraregional LNs identified by EUS guided tissue acquisition

Inclusion Criteria:

• Presumed resectable pCCA OR
• Presumed resectable iCCA OR
• Presumed resectable mid-common bile duct CCA OR
• Presumed unresectable pCCA worked-up for Liver Transplantation AND
• Written informed consent must be given according to International Council on Harmonisation/Good Clinical Practice guidelines, and national/local regulations AND
• Age > 18 years.

Exclusion Criteria:

• Patients with a history of treated CCA
• Patients with CCA for which a pancreatoduodenectomy is indicated, based on cross-sectional imaging
• Patients with a history of treated liver malignancy
• Patients with a contra-indication for EUS-tissue acquisition (f.e. uncorrectable coagulopathy or platelet disorder), in line with current clinical practice

Patients with suspected iCCA or pCCA who have a presumed resectable carcinoma will be invited to participate. Patients with CCA distal from the cystic junction but proximal from the pancreatic body are eligible for inclusions as well, as treatment is similar to Bismuth I pCCA. In other words, all patients with CCA that is not distal CCA for which a pancreato-duodenectomy is indicated, are eligible for inclusion. Also patients with presumed unresectable pCCA who are worked-up for liver transplantation are invited to participate. At time of inclusion a definitive diagnosis of iCCA/pCCA is not obligatory, since definitive diagnosis of CCA is sometimes confirmed during the preoperative EUS through EUS guided biopsy of the mass. The probable diagnosis of iCCA/pCCA and the suspected resectability will be established during the multidisciplinary meeting, based on clinical symptoms, cross-sectional imaging, endoscopy and laboratory tests.

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