PCSK9 and neoplasm: The molecular mechanism by which CTL killed PCSK9-deficient tumor cells involved an increase in the tumor cell surface MHC I (Major Histocompatibility Complex I) expression in PCSK9-deficient tumors as compared to control, indicating that PCSK9 downregulates MHC I surface levels by lysosomal degradation in a manner very similar to the downregulation of LDLR protein levels [94].