Experimental: A: Experimental

Patients will receive surveillance with liver enzymes, CA 19-9, history, clinical evaluation of signs of recurrence (e.g. weight loss, abdominal pain or fatigue) in combination with analysis of plasma ctDNA (90 ml blood drawn per visit) every 3 months until disease progression or up to 36 months. If plasma ctDNA is positive the patient will have a CT scan (thorax and abdomen) and EUS every 3 months for 2 years and then every 6 months until disease recurrence or up to 36 months. If plasma ctDNA is negative the patient will have CT scan of thorax and abdomen and EUS every 6 months until disease recurrence or up to 36 months. Plasma eccDNA will be determined at the same time as ctDNA but a positive eccDNA result will not be informed to the patients.

No_intervention: B: Control

Patients will receive surveillance until recurrence according to current Danish guidelines with liver enzymes, history and clinical evaluation every 3 months for two years and then every 6 months until 36 months. If an increase in liver enzymes is seen or clinical signs of recurrence (e.g. weight loss, abdominal pain or fatigue) patients will have a CT scan of thorax and abdomen. Blood samples (90 ml blood per visit) will be collected at the same time points as blood is drawn for liver enzymes (i.e. every 6 months until 36 months) for later analysis at the end of study of plasma ctDNA and eccDNA. These measurements will serve to enable post-trial comparison of oncological outcomes for the two arms.