Advanced Solid Malignant Tumors (With Positive Expression of MSLN in Tumor Tissue)

1. Study Title: Efficacy and safety of MSLN CAR-T in advanced malignant tumors 2. Study Objectives: Primary: To evaluate the safety and tolerability of MSLN-targeted CAR-T cell therapy in patients with stage III/IV advanced malignant tumors. Secondary: To preliminarily evaluate the efficacy of MSLN-targeted CAR-T cell therapy in this patient population. Exploratory: To assess in vivo expansion and persistence of infused MSLN-targeted CAR-T cells and explore correlations with clinical outcomes. 3. Participant Intervention: Participants will receive lymphodepleting chemotherapy (FC regimen: Fludarabine + Cyclophosphamide) on Days -5, -4, and -3 relative to the planned MSLN CAR-T cell infusion. The CAR-T cell infusion will be administered 72 hours after the completion of the FC chemotherapy.