IMMUNO-FIT Observational Study

Inclusion Criteria: * Age ≥18 years * Histologically confirmed solid malignancy * Receiving immune checkpoint inhibitors in one of the following settings: * Adjuvant: Single-agent anti-PD-1, anti-PD-L1, or anti-CTLA-4 * Metastatic/Palliative: Single-agent or dual-agent anti-PD-1, anti-PD-L1, or anti-CTLA-4 * ECOG Performance Status 0-2 * Able to perform cardiopulmonary exercise testing * Able to provide written informed consent * Willing and able to comply with study procedures and follow-up schedule Exclusion Criteria: * Age \<18 years * Prior systemic anti-cancer immunotherapy for unresectable or metastatic disease, EXCEPT: * Prior adjuvant or neoadjuvant immunotherapy if all treatment-related adverse events have returned to baseline or stabilized * Prior anti-PD-1, anti-PD-L1, or anti-CTLA-4 therapy with at least 6 months since last dose and date of disease recurrence * Absolute contraindications to cardiopulmonary exercise testing: * Acute myocardial infarction within 6 weeks * Unstable angina * Uncontrolled cardiac arrhythmias causing symptoms or hemodynamic compromise * Active endocarditis * Symptomatic severe aortic stenosis * Uncontrolled heart failure * Acute pulmonary embolism or pulmonary infarction * Acute myocarditis or pericarditis * Suspected or known dissecting aneurysm * Acute systemic infection * Inability to perform cardiopulmonary exercise testing (e.g., severe lower limb dysfunction, severe peripheral vascular disease) * Inability to provide informed consent * Currently enrolled in another interventional clinical trial that would confound study outcomes ADDITIONAL EXCLUSION CRITERIA FOR RESEARCH BIOPSY SUB-STUDY: * Severe cardiopulmonary disease precluding safe sedation (for endoscopic biopsies) * Suspected bowel obstruction or perforation (for gastrointestinal biopsies) * Uncorrectable severe coagulopathy (INR \>1.5, platelet count \<50,000/µL) * Severe portal hypertension with high-risk varices (for upper endoscopy) * Lesion inaccessible for safe biopsy as determined by a performing clinician