ESR1 and invasive ductal breast carcinoma: Our previous pathological study with paraffin-embedded breast cancer biopsies has shown that GP88 is expressed in ER+ invasive ductal carcinoma (IDC) in association with poor prognosis whereas GP88 expression was negative in benign lesions and normal mammary epithelial tissues [31] supporting the fact that GP88 could play a role in clinical outcomes of breast cancer patients.