Participants identified with postoperative delirium will be asked (at the routine follow-up meeting after surgery) to participate in an qualitative interview in order to understand the participant's experience of postoperative delirium.

All included participants in the CASE-study.

• The assessment of cognitive function will be performed using the validated 4AT Test (4AT). Cognitive impact will be assessed at baseline before neoadjuvant chemotherapy (if chemotherapy is indicated) and at patient admission for surgery, postoperative day 1, 3 and 7, and at follow-up 4-8 weeks after surgery.
• Risk factors for POD will be explored by investigate the relationship between postoperative delirium, chemotherapy preoperative depression, frailty, quality of life, malnutrition and sarcopenia. Patients will report health-related quality of life using the validated EORTC QLQC-C30 and EORTC QLQ-OG25 questionnaires. Frailty and depression will be measured preoperatively with Clinical Frailty Scale (CFS-9) and the Patient Health Questionnaire (PHQ-9). Malnutrition is evaluated by using Patient-Generated Subjective Global Assessment (PG-SGA). Sarcopenia is assessed through CT-scan, which is conducted as part of clinical routine.

The assessment of cognitive function will be performed using the validated 4AT Test (4AT).

Cognitive impact will be assessed at baseline before neoadjuvant chemotherapy (if chemotherapy is indicated) and at patient admission for surgery, postoperative day 1, 3 and 7, and at follow-up 4-8 weeks after surgery.

A risk factor for postoperative delirium is preoperative depression. Depression will be measured preoperatively with the Patient Health Questionnaire (PHQ-9).

All participants that suffered from POD will be invited to participate in an interview, with a maximum number of 25 participants. A semi-structured one-on-one interview with the aim to describe patient experiences of POD will be used. The semi-structured interview technique allows the interviewer to ask probing questions for clarification when necessary. An interview guide will be used to ensure covering issues such as cognition, memory loss, attention, awareness and orientation to the environment. The participant will be asked for participation at the follow-up meeting after surgery. The interview takes place 2 weeks after follow up-meeting after surgery at the location (or via that media) that best serve the participant. The interview will be recorded and transcribed, then analysed using qualitative content analysis with an inductive and latent approach.