IMMUNO-FIT Observational Study

This observational study will investigate how immunotherapy affects physical fitness, quality of life, and treatment tolerance in adults with solid cancers. Immunotherapy can cause a range of side effects that impact daily functioning and may lead to treatment delays or early discontinuation. Physical fitness may influence how well patients cope with treatment, yet little is known about how fitness changes during immunotherapy or whether baseline fitness is linked to outcomes. Participants will complete fitness testing using cardiopulmonary exercise testing (CPET) and quality-of-life questionnaires before starting immunotherapy and again 12 weeks later. Blood samples will also be taken, and long-term outcomes including survival, disease progression, and quality of life will be followed for up to 24 months. All cancer treatment will remain standard of care. A small number of participants will be invited to take part in an optional research biopsy at week 12 to explore how physical fitness relates to changes in the tumour's immune environment. The study will help researchers understand natural changes in fitness during immunotherapy, identify whether baseline fitness is associated with treatment tolerance or outcomes, and generate information needed to design future trials testing exercise-based interventions during immunotherapy.