CTLA-4: As an Immunosuppressive Immune Checkpoint in Breast Cancer.

Breast cancer (BC) is one of the prevalent diseases and causes of death in women, and its incidence rate is increasing in numerous developed and developing countries. The common approach to BC therapy is surgery, followed by radiation therapy or chemotherapy, which doesn't lead to acceptable outcomes in many patients. Therefore, developing innovative strategies for treating BC is essential for the most effective therapy. The immunotherapy of BC is a promising and attractive strategy that can increase the immune system's capacity to recognize and kill the tumor cells, inhibit the recurrence of the tumors, and develop new metastatic sites. The blockade of immune checkpoints is the most attractive and promising strategy for cancer immunotherapy. The cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is a cellsurface glycoprotein expressed by stimulated T cells and has pivotal roles in cell cycle modulation, cytokine generation, and regulation of T cell proliferation. Currently, anti- CTLA-4 agents such as monoclonal antibodies (Ipilimumab and tremelimumab) are broadly applied as therapeutic agents in clinical studies of different cancers. The anti- CTLA-4 antibodies, alone or combined with other therapeutic agents, remarkably increased the tumor-suppressive effects of the immune system and improved the prognosis of cancer. The immune checkpoint inhibitors may represent promising options for BC treatment as in monotherapy or in combination with other conventional treatments. In this review, we discuss the role of CTLA-4 and its therapeutic potential by inhibitors of immune checkpoints in BC therapeutics.