Abstract
Breast cancer is the most commonly diagnosed cancer in women and is one of the leading causes of death from cancer in women worldwide. Despite the significant benefits of using conventional chemotherapy in the treatment of breast cancer, one of its subtypes, the triple-negative breast cancer, is still a challenge in clinical practice. Recent studies have been investigating the role of the immune system in breast cancer and the development of immunotherapy. Although recently the use of atezolizumab, an anti-PD-L1 monoclonal antibody, combined with chemotherapy was approved, an important step in the treatment of patients with triple-negative metastatic breast cancer, the use of immunotherapy to treat breast tumors remains a major challenge. In this systematic literature review, following PRISMA guidelines, we searched for clinical trials using immunotherapy in the treatment of metastatic triple-negative breast cancer published until March 2020 in the databases EMBASE, PubMed and Cochrane Central Register of Controlled Trials (CENTRAL), with no language restrictions. We did not contact the authors of the clinical trials to obtain additional information. Two researchers independently collected the data and assessed the quality of this study. The literature shows that immunotherapy with anti-PD-1/PD-L1 agents is emerging as a new treatment option in breast cancer. On the other hand, when compared to other types of cancer in which several agents have already been approved, the research is still in its infancy. The use of anti-PD-1/PD-L1 agents as monotherapy revealed encouraging results in the metastatic setting, especially when administered in the early course of the disease, although combination strategies with chemotherapy appear to increase its efficacy. The main limitation of this study is the approach of cancer only in advanced stages.