High numbers of tumor-infiltrating lymphocytes (T-, B-, natural killer [NK] and NKT cells) are generally associated with more favorable clinical outcomes in breast cancer, especially in patients with HER2-positive and triple-negative tumors [5,6,7,8,9,10,11,12] but also in estrogen receptor (ER) positive disease [13]. This evidence concerns the gene ESR1 and neoplasm.