Because EGFR and ErbB2 play a very important role in the development of breast cancer, and constitutive STAT3 tyrosine or serine phosphorylation is frequently observed in breast carcinomas40, 41, PTPN9 may contribute to tumor suppression by dephosphorylation of EGFR, ErbB2 and STAT3 and silencing of ErbB and STAT3 signaling pathways, thereby having potential therapeutic value for breast cancer. The gene discussed is STAT3; the disease is breast cancer.