Identification of Changes in Cancer-related Fatigue and Physical Activity and Their Association in Patients With Inoperable Lung Cancer: a Longitudinal Observational Study

Inclusion Criteria: * Locally advanced irresectable or metastatic lung cancer (all histologies including NSCLC and SCLC). * ≥18 years. * ECOG performance status of ≤2 (a lower score indicates a higher performance status), assessed by the clinician (10). * Planned to start a first-line systemic treatment consisting of chemotherapy and/or immunotherapy. Patients who receive radiotherapy, concurrently or sequentially, within a multimodality treatment approach for locally advanced lung cancer are allowed. * Ability to give informed consent. Exclusion Criteria: * Being planned for primary radiotherapy with radical intent only or treatment with targeted therapies (mostly tyrosine kinase inhibitors (TKI's)). * Having complicated or unstable bone metastases (as judged by the clinician). * Unstable heart disease, including unstable congestive heart failure, arrythmia, or myocardial infarction diagnosed within the last 3 months. * Other malignancies in the last 2 years (except for adequately treated basal cell, superficial or in situ cancer of the bladder or the cervix). * Have musculoskeletal problems precluding them to be physically active. * Not understanding and speaking Dutch.