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

The goal of this observational study is to learn how fatigue changes during lung cancer treatment and how it relates to physical activity levels in adults with locally advanced, inoperable, or metastatic lung cancer who are starting chemotherapy and/or immunotherapy. The main questions to answer are: * How do fatigue and physical activity levels change throughout lung cancer treatment? * How are changes in fatigue related to physical activity levels on the short- and long term? Participants will: * Complete questionnaires on fatigue, breathlessness, sleep quality, quality of life, stress, anxiety and depression at multiple time points. * Wear activity monitors during four measurement periods to assess daily physical activity. * Complete brief daily smartphone questionnaires on fatigue, breathlessness, pain, and perceived ability to walk. * Wear a smartwatch throughout the study. * Undergo physical assessments, including a 1-minute sit-to-stand test, a thigh muscle strength test, and a frailty assessment. * Attend six study visits over the course of the study, some of which may be scheduled alongside routine hospital appointments.