two human cancer cell lines HepG2 and A431, that up to 40% of the Cys215 residues in PTP1B can be selectively irreversibly oxidized under these cellular conditions resulting in non-functional PTP1B. In addition, PTPN1 genetic ablation in p53 deficient mice resulted in an increased incidence of lymphomas and a decrease in overall survival rates. In contrast, the PTPN1 gene has been shown to be overexpressed in conjunction with HER2 in breast cancer cases. Murine models of HER2 overexpression in conjunction with PTPN1 knockout resulted in delayed tumor growth and with fewer observed metastases to the lung suggesting that PTPN1 may have an oncogenic role in breast cancer. See also Protein tyrosine phosphatase References