Immunotherapy of Breast Cancer

Cancer immunoediting is the process by which the immune system protects the host from tumor development and guides the somatic evolution of tumors by eliminating highly immunogenic tumor cells. A fundamental dogma of tumor immunology and of cancer immunosurveillance in particular is that cancer cells express antigens that differentiate them from their nontransformed counterparts. Molecular studies clearly show that these antigens were often products of mutated cellular genes, aberrantly expressed normal genes, or genes encoding viral proteins. There is a strict correlation between genetic instability and the immune landscape of a breast cancer. Mutational heterogeneity in breast cancer is associated with new cancer-associated genes and new cancer antigens. Frequencies of somatic mutations or mutational burden can be related to the immunogenicity of breast cancer. We believe that molecular subtypes of breast cancer that are triple negative, luminal B-like or HER2-positive have a high mutational burden and can be considered immunogenic. The increasing knowledge of the immune system's capacity to not only recognize and destroy cancer, but also to shape cancer immunogenicity will develop more informed attempts to control cancer via immunological approaches. To be effective in breast cancer, immunotherapies will have to increase the quality or quantity of immune effector cells, reveal additional protective tumor antigens, and/or eliminate cancer-induced immunosuppressive mechanisms. Multiple immunotherapy approaches are under investigation in patients with breast cancer. These include vaccine approaches to elicit strong specific immune responses to tumor antigens such as WT-1, HER2 and NY-ESO-1, approaches involving adoptive transfer of in vitro-expanded, naturally arising or genetically engineered tumor-specific lymphocytes, therapeutic administration of monoclonal antibodies to target and eliminate tumor cells, and approaches that inhibit or destroy the molecular or cellular mediators of cancer-induced immunosuppression, such as CTLA-4, PD-1 or Treg cells. Here we provide a concise and comprehensive review on the role and utility of promising immunotherapeutics for the treatment of patients with breast cancer.