APOC1 (apolipoprotein C1) is a plasma lipoprotein that inhibits lipoprotein binding to multiple receptors (LDL receptor, LDL receptor-related protein, and VLDL receptor) and associates with HDL and triglyceride-rich lipoproteins 1. Beyond classical lipid metabolism, APOC1 has emerged as a key immunoregulatory factor in cancer and inflammatory disease contexts. In hepatocellular carcinoma, APOC1 is overexpressed in tumor-associated macrophages (TAMs), and its inhibition promotes M2-to-M1 macrophage transformation via ferroptosis, enhancing anti-PD1 immunotherapy efficacy 2. Similarly, APOC1 serves as a prognostic biomarker in ovarian cancer, correlating with M2 macrophage infiltration and poor clinical outcomes 3. In esophageal squamous cell carcinoma, APOC1+ macrophages mediate key intercellular communications within metastatic microenvironments 4. APOC1 expression also associates with advanced fibrotic disease in keloids and marks immunosuppressive macrophage populations in acute-on-chr19 liver failure, where it correlates with lipid metabolic reprogramming 56. Additionally, APOC1 is a functional regulatory variant in Alzheimer's disease pathogenesis 1. These findings indicate APOC1 functions not only in lipid transport but also as a regulator of macrophage polarization and tumor immunosuppression.