ESR1 and invasive ductal breast carcinoma: We selected 36 cases of invasive ductal carcinoma of no special type (IDC) (20 cases of estrogen receptor (ER)-positive cancer and 16 cases of ER-negative cancer) along with 18 normal tissues from the archives of the Department of Pathology at Aichi Medical University Hospital, based on the availability, and served them for immunohistochemical analysis.