BST2 is an interferon-induced antiviral restriction factor that functions as a physical tether to block the release of diverse enveloped viruses 1. The primary mechanism involves direct tethering of nascent virions to infected cell membranes, preventing their spread as cell-free particles 2. BST2 restricts multiple virus families including retroviruses (HIV-1, HIV-2), filoviruses (Ebola, Marburg), and others such as hepatitis C virus and respiratory syncytial virus 3. Beyond antiviral functions, BST2 exhibits context-dependent roles in disease. In viral infections, BST2 suppresses replication through selective autophagy-mediated degradation of viral nucleocapsid proteins via the MARCHF8-CALCOCO2 axis 1. Conversely, in cancer contexts, BST2 expression correlates with poor outcomes. Elevated BST2 in esophageal squamous cell carcinoma, colorectal cancer, and pancreatic cancer associates with increased tumor-associated macrophage infiltration and M2 polarization, promoting tumor progression 456. In nasopharyngeal carcinoma, the CEACAM7-JAK2/STAT3-BST2 axis drives cell migration 7. BST2 polymorphisms influence HIV transmission susceptibility through innate immune mechanisms 8. These findings reveal BST2 as a potent antiviral molecule whose aberrant expression in tumors paradoxically supports malignant progression through immune modulation.