<h4>Introduction</h4>Tumor-infiltrating lymphocytes (TILs) are established biomarkers in triple-negative and human epidermal growth factor receptor 2 (HER2)-positive breast cancers; however, their clinical significance in hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer remains unclear. The gene discussed is ERBB2; the disease is breast carcinoma.