ESR1 and invasive ductal breast carcinoma: Biochemical analysis of the biopsy samples pre and post neoadjuvant therapy revealed a varied response in HER3 expression as demonstrated in Fig. 3B. Interestingly, we saw significant HER3 increase (P = 0.0004) in Subject 16, who had ER+ (ER+/PR+ /HER2-) invasive ductal carcinoma.