CTLA4 and breast cancer: Using TIL gene signatures in luminal A and luminal B BC, predictive responses of immune checkpoint inhibitors, such as anti-CTLA4 and anti-PD1 (Figure 1), allow stratification into three subtypes: (1) Lum 1, with low TILs and immune gene levels, (2) Lum 2, high expression of STAT1 and interferon-stimulated genes with TP53 somatic mutations, and (3) Lum 3, high level of TILs and immune-related/immune checkpoint gene expression (i.e., PD-L1 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)) and chemokine genes (i.e., CXCL9 and CXCL10) and their receptors [30].