Progress and pitfalls in the use of immunotherapy for patients with triple negative breast cancer

INTRODUCTION: Triple negative breast cancer (TNBC) is an area of high unmet medical need in terms of new effective treatment strategies. Although breast cancer is traditionally considered a 'cold' tumor type, TNBC is the most appropriate subtype for immunotherapeutic strategies; this is due to the high level of tumor infiltrating lymphocytes, PD-L1 expression, and tumor mutational burden compared to other breast cancer subtypes. AREAS COVERED: This review examines the available evidence on the use of immunotherapeutic strategies in early and advanced TNBC, discusses the pitfalls and limitations often encountered in clinical research, and summarizes data on novel promising immunomodulatory approaches that have been explored in early-phase trials. EXPERT OPINION: Triple-negative breast cancer (TNBC); breast cancers (BCs); estrogen receptor (ER); progesterone receptor (PgR); human epidermal growth factor-2 (HER-2); basal-like 1 (BL1), basal-like 2 (BL2); mesenchymal (MES); mesenchymal stem-like (MSL); immunomodulatory (IM); luminal androgen receptor (LAR); basal-like immunosuppressed (BLIS); basal-like immune-activated (BLIA); tumor-infiltrating lymphocytes (TILs); tumor mutational burden (TMB); immune cells (ICs); immunohistochemistry (IHC); overall response rate (ORR); overall survival (OS); progression-free survival (PFS); intention-to-treat (ITT); hazard ratio (HR); confidence interval (CI); Food and Drug Administration (FDA); European Medicines Agency (EMA); immune checkpoint inhibitors (ICI); Combined Positive Score (CPS); disease control rate (DCR); neoadjuvant chemotherapy (NACT); pathological complete response (pCR); event-free survival (EFS); disease-free survival (DFS); residual cancer burden (RCB); San Antonio Breast Cancer Symposium (SABCS); antibody-drug conjugates (ADCs); PARP inhibitors (PARPi); clinical benefit rate (CBR); Histone deacetylase inhibitors (HDACi); Dendritic cell (DC); talimogene laherparepvec (TVEC); granulocyte-macrophage colony-stimulating factor (GM-CSF); mismatch repair deficiency (dMMR).