Checkpoint Inhibitors in Breast Cancer - Current Status and Future Directions.

Antineoplastic agents directly targeting tumor cells have represented the major strategy of systemic anticancer therapy for many years. Nevertheless, overcoming resistance mechanisms remains a great challenge because treatment options are limited in many cases. From this point of view, immunotherapeutic approaches seem promising in a broad spectrum of solid tumors. These include in particular the currently available inhibitors directed against immune checkpoints leading to a significant T-cell activation. To date, the programmed death receptor 1 (PD-1) and its ligand are the most prominent targets in this context. However, the role of checkpoint inhibitors in the treatment of breast cancer is still being debated, and the main focus is on triple-negative breast cancer patients as a target population in many ongoing trials. Moreover, the potential superiority of combinations with other anticancer drugs such as cytotoxics and targeted agents will be discussed.