To determine the in vitro efficacy of the FAK-I BI 853520 in repressing Y397-FAK phosphorylation in differentiated breast cancer cells and in breast cancer cells that have undergone an epithelial–mesenchymal transition (EMT) and also to test the generality of the findings, we employed a combination of various murine mammary cancer cell lines. This evidence concerns the gene PTK2 and breast carcinoma.