ESR1 and breast carcinoma: Invasive lobular carcinoma (ILC) is the second most common subtype of breast cancer, which has some similar clinicopathological features to TC, such as up to 90% of ILCs have positive estrogen receptor (ER) and negative human epidermal growth factor receptor‐2 (HER2), with low malignancy and a favorable prognosis.5, 6