PTK2 and breast carcinoma: Prior reports showed that PTPN12 acts as a negative regulator of tyrosine phosphorylation not only of p130cas and FAK as previously reported in other cells but also of TrkB [28, 29]; promoter CpG island hypermethylation occurs more frequently in breast cancer cases and breast cancer cell lines with low PTPN12 expression [27], indicating that it is a potentially mechanism leading to PTPN12 downregulation.