Immune checkpoint inhibitors: a potential treatment breakthrough for metastatic triple-negative breast cancer?

A milestone in oncology has been reached in recent years with the advent of immune checkpoint inhibitors (ICIs) which target programmed cell death protein 1 (PD-1) or its ligand, PD-L1, and cytotoxic T-lymphocyte-associated protein 4 (CTLA4). ICIs were first approved by the Food and Drug Administration (FDA) for melanoma in 2011 and subsequently in several other tumor types. In contrast to more immunogenic solid tumor types, breast cancer (BC) is typically not characterized by a high tumor mutation burden which is known as one of the predictive biomarkers of response to ICI (well described in melanoma and lung cancer), and so it has been considered potentially less immunogenic.