Label-free proteomic analysis was performed in HER2-overexpressing breast cancer cell lines to reveal the proteins that were significantly different in the BT474 cell line in response to afatinib, neratinib or lapatinib treatments and also in the breast cancer cell lines SKBR3 and HCC1954 in response to neratinib treatments. Here, ERBB2 is linked to breast carcinoma.