CTLA4 and cancer: Studies by Blazquez et al., 2018, have shown that the PI3K/AKT/mTOR pathway leads to the increased expression of immune-related genes (PD-L1, CSF1, and CSF1R) or cytotoxic T-lymphocyte-associated protein 4 (CTLA4) in microglia or cancer cells within the brain metastasis microenvironment.