Studies over the past decade have suggested that the presence of tumor-infiltrating lymphocytes (TILs) is prognostically significant in breast cancer.1–3 In addition, immune therapy in conjunction with chemotherapy has been successful in treating Triple-Negative Breast Cancer (TNBC)4,5 However, 70-80% of breast cancers are ER+ and not eligible for immunotherapy under current guidelines.6–8 Nevertheless, these tumors often have moderate immune infiltration. The gene discussed is ESR1; the disease is breast cancer.