What is the role of immunotherapy in breast cancer?

The immune system plays a complex role in the recognition/prevention, early eradication as well as progression of cancer. Recently, we have witnessed great momentum in the field of immuno-oncology. Checkpoint inhibitors and chimeric antigen receptor T cell therapy have now entered the clinic, with impressive and durable clinical responses seen across a broad array of tumor types. There are several lines of evidence supporting the development of an immune targeted approach in breast cancer. Emerging data of early clinical trials evaluating monotherapy checkpoint inhibition have shown modest activity in breast cancer, in particular high grade and aggressive subtypes such as triple negative, human epidermal growth factor receptor 2 (HER2)-positive and luminal B breast cancers. A considerable amount of effort is currently underway in exploring the use of combinatory strategies where therapies with distinct and potentially complementary mechanisms of actions may further enhance the immune response broadening out the group of breast cancer patients who would benefit from this strategy of cancer treatment. In this review, we discuss approaches to targeting the immune system in breast cancer adopted through understanding why the host immune system has failed in natural tumor suppression as well as the processes evolved by the tumor to circumvent an active immune system.