Changes of health-related quality of life 6 months after high-risk oncological upper gastrointestinal and hepatobiliary surgery: a single-centre prospective observational study (ChangeQol Study). - Maillard J; Elia N; Ris F; Courvoisier DS; Zekry D; Labidi Galy I; Toso C; Mönig S; Zaccaria I; Walder B (BMJ open, 2023)