Feasibility and Expansion Trial of Transcutaneous Vagus Nerve Stimulation (tVNS) for Immune-Related Fatigue in Patients Receiving Immune Checkpoint Inhibitors

Inclusion Criteria: * Age 18 years or older * Histologically confirmed advanced or metastatic solid tumor * Receiving immune checkpoint inhibitor therapy and completed at least two cycles * Clinically significant fatigue (FACIT-F score ≤ 34) * ECOG performance status 0-2 * Life expectancy of at least 3 months * Ability to provide informed consent * Access to a smartphone or tablet Exclusion Criteria: * Current or planned chemotherapy, targeted therapy, or radiation during the 4-week intervention period. * Have received targeted therapy in the last 2 weeks * Have received chemotherapy or radiation therapy in the last 4 weeks * Symptomatic brain metastases defined as active neurologic complaint (headache, blurry vision, neurologic deficits or other symptom requiring treatment with steroids) * Long term steroid use \>10 mg prednisone equivalent daily * Active autoimmune disease requiring systemic immunosuppression * Implanted electronic medical devices (e.g., pacemakers, defibrillators) * History of epilepsy or vagal hypersensitivity * Known arrhythmia or bradycardia (Baseline HR \< 50 bpm) * Open wounds or dermatologic issues at the stimulation site * Pregnancy or breastfeeding * Participation in other fatigue-focused intervention trials * Severe uncontrolled psychiatric illness (PHQ-9 \>20)