ESR1 and breast cancer: Similarly, discordance values of 28.9%, 23.7%, and 8.9% for ER, PR, and HER2, respectively, were observed in a group of 190 BC cases (44), 8.8% and 11.3% discordance was observed for ER and HER2 expression in 80 cases of invasive ductal BC (45), and 28.8%, 31.7%, 13.5%, and 43.3% discordance in ER, PR, HER2, and Ki-67 expression was found between PTs and matching ALN metastases (46).