A 57-year-old postmenopausal woman was diagnosed with left breast invasive lobular carcinoma, hormone receptor–positive, human epidermal growth factor receptor 2–negative (HR+/HER2−), K67 index of 5–10%, and classified as pT3N3aM0 (stage IIIC). This evidence concerns the gene ERBB2 and invasive lobular breast carcinoma.