PTK2 and breast cancer: Recent studies have shown that β1 integrin overexpression or engagement by FN activates STAT3 signaling pathway via JAK2, SRC or FAK adaptor proteins, which participates in breast cancer progression or their resistance to HER2-targeting small-molecule inhibitors [40, 41], as has found β1 integrin in mediating resistance of lung cancer to EGFR-targeting drugs [42, 43].