ERBB2 and cancer: FAK is an intracellular tyrosine kinase that is overexpressed and/or activated in several types of cancers with established roles in regulating tumor progression and metastasis.36 We determined that Ptk6+/+ MMTV-ERBB2 mice exhibited increased levels of active FAK, phosphorylated on tyrosine residues 576/577 (Figure 4a).