Risk of SARS-CoV-2 infection and disease in metastatic triple-negative breast cancer patients treated with immune checkpoint inhibitors

Metastatic triple-negative breast cancer (mTNBC) is an aggressive disease with particularly poor outcomes [1]. Over the past few years, relevant gains in knowledge concerning the molecular landscape of this disease have allowed to considerably broaden the available therapeutic armamentarium. Poly ADP-ribose polymerase-1 inhibitors, epigenetic agents, anti-androgens, tyrosine kinase inhibitors and immune checkpoint inhibitors (ICIs) may all optimally exemplify the targeted therapeutic weapons recently gained in the fight against mTNBC [2]. Targeting of immune checkpoints through their respective monoclonal antibodies translates into effective antitumor responses not only in widely recognized ‘immunogenic’ tumor types, for example, melanoma and renal cell carcinoma, but also in other solid tumors including breast cancer [3]. PD-1 is an immune checkpoint expressed on the surface of B cells, T cells and natural killer T cells, with a critical role in modulating self tolerance, immune homeostasis and inflammation. When activated by PD-L1 or -L2, PD-1 mediates downregulation of T-cell activity, causes T-cell lysis and reduces cytokine production significantly