Tumor Infiltrating Lymphocytes in Breast Cancer: Why Is It Useful to Know?

Stromal tumor infiltrating lymphocytes (sTILs) in breast cancer is an easily evaluable histopathological biomarker that is shown to be robust and reproducible with prognostic and predictive value in triple negative breast cancer (TNBC), HER2+, and high-risk luminal breast cancer. sTILs can be assessed using a light microscope on H&E-stained slides. sTILs also predict therapeutic response to chemotherapy and immunotherapy in the neoadjuvant setting, with higher sTILs score on baseline biopsies associated with higher pCR rates and better outcomes. sTILs have a potential role in therapy de-escalation/optimization strategies, and in the selection of patients for immunotherapy.