PTK2 and breast carcinoma: In order to investigate whether ROS1 inhibitors affect FAK signaling to overcome drug resistance in CDH1-deficiency cancers, such as gastric and breast cancers, we first used Western blot analysis to determine ROS1 and FAK signaling activity levels by examining phosphorylation of their downstream targets in five cancer cell lines (SNU-668, NUGC-4, MGC-803, MDA-MB-231, and Hs-578t) across 12 hours of treatment with crizotinib/entrectinib.