PTK2 and breast cancer: For example, the importance of focal adhesion kinase (FAK) within the tumour cell compartment in driving tumour proliferation and metastasis is well documented and has led to the development of a number of small-molecule inhibitors, which are currently under clinical evaluation.100 Interestingly, fibroblast-directed deletion of FAK, in a genetically engineered mouse model of breast cancer, reduced metastasis but had no effect on primary tumour growth.