Among them, basigin-1 is a retina specific CD147 containing an additional unglycosylated domain [39,40]; basigin-3 or basigin-4, less expressed in normal and tumor human tissues, contains a single extracellular domain (IgI), and basigin-3 serves as an endogenous inhibitor of basigin-2 via hetero-oligomerization. Here, BSG is linked to neoplasm.