PTK2 and cancer: In addition to the facts that FAK overexpression in primary tumours of patients with HNSCC is associated with lymph node metastasis and that there is an almost perfect correlation between the expression levels of FAK found in the primary tumour and in the corresponding metastasis, observations from these studies support the importance of FAK as a mediator of metastatic HNSCC cancer progression via the regulation of MMP-2 expression.