Immunotherapy for triple-negative breast cancer

Breast cancer (BC) is the most common cancer and one of the leading causes of cancer death in women. Triple-negative breast cancer (TNBC) is a typical subtype of breast cancer with lack of estrogen and progesterone receptors and has low expression levels of human epidermal growth factor receptor 2 (HER2), accounting for 15%–20% of all BC cases. In comparation with other subtypes of BC, TNBC displays stronger invasiveness, higher recurrence rate and poorer prognosis. Due to lack of targeted therapies and limited benefit from chemotherapy, abundant investigations have been committed to discover effective molecular targets and treatment approaches for TNBC patients. During the past decade, emerging evidence has shown that compared to other subtypes of BC, TNBC is more immunogenic, has higher expression levels of programmed death ligand-1 (PD-L1) and higher rates of CD8+ T cell infiltration. Thus, TNBC is deemed to be most suitable for immunotherapy among all BC subtypes.