SPP1 and neoplasm: The mIHC staining revealed that SPP1 tended to localize at the tumor boundary, whereas CD8+ T cells were likely to localize outside of the tumor, further confirming the immunosuppressive role of SPP1. Typically, among the three classification phenotypes, the expression of SPP1 was markedly elevated in the C3 compared with the C1 and C2 subtypes, which may partially explain the immunosuppressive microenvironment within C3.