Immunotherapy for Early-Stage Triple-Negative Breast Cancer

Early-stage triple-negative breast cancers, which lack expression of three proteins (estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2), have long been defined by what they are not. Now they have found a new identity and treatment approach: they are breast cancers that benefit from immune checkpoint inhibitor therapy. Triple-negative breast cancer is characterized by higher tumor expression of the immunomodulatory protein programmed death ligand 1 (PD-L1), greater tumor mutational burden, and more extensive tumor-infiltrating lymphocytes than other breast cancer subtypes — all of which suggested potential benefit from immunotherapy. The survival data from the KEYNOTE-522 trial that . . .