PTK2 and head and neck squamous cell carcinoma: Most importantly, Chiu et al. indicated that the immunoreactivity of FAK and FAK-pY397 was especially evident in metastatic oral lesions and positively correlated with the degree of malignancy by immunohistochemical staining, indicating that FAK and its phosphorylated form were associated with tumor invasion and metastasis in HNSCC [40].