Among the ongoing clinical trials in breast cancer, a phase I trial using a triple combination of anti-CTLA-4 and anti-PD-1 antibodies, and a small-molecule epigenetic modulator, entinostat, tests safety, efficacy and impact on the ratio of tumor-specific effector T cell (Teff) to regulatory T cell (Treg) (NCT02453620). Here, CTLA4 is linked to breast cancer.