Relationship Of Prognosis And Expression Of PTPN12in Various Molecular Subtypes Of Breast Cancer

Background and objective:Breast cancer is one of the most common malignancies affecting women. The statistics data showed230thousands patients were diagnosed with breast cancer in the United States in2011, which was the highest incident rate among female cancers. Also, there were another40thousand patients died from breast cancer in America last year. In China, breast cancer accounts for7%～10%of all human malignancies. The newly discovered breast cancer patients were increasing year by year. In the past10years, the incidence of female breast cancer in Shanghai, Beijing, Shenzhen and other big cities rose significantly, even being the biggest group in female malignant cancers. Breast cancer is seriously affecting people’s normal life, distroying women’s physical and mental health, even endanger women’s life. For a long time, how to effectively prevent and treat breast cancer has been become the focuse of research in oncology.With the development and application of the modern molecular biology in breast cancer research area, people gradually found that breast cancer was a highly heterogeneous disease, the breast cancer patients were obviously different from each other. Breast cancer is divided into all kinds of molecular subtype according gene expression. Different molecular subtypes of breast cancer have different biological behaviour and responses to therapy. The individual therapy, combining the tumor molecular subtypes to clinical stage the of breast cance patients,has become an important treatment mode in breast cancer field. At present, according to estrogen receptor (ER) and progesterone receptor (PR) expression, and epidermal growth factor receptor2(HER-2) amplification or overexpress, breast cancer is divided into three kinds of molecular subtype. Among them, the Triple-Negative breast cancer(TNBC), which lack expression of estrogen receptor(ER), progesterone receptor (PR) expression and amplification of receptor tyrosine kinase HER-2(the epidermal growth factor receptor-2),accounting for20percent of breast cancer, is more aggressive, with a higher likelihood of recurrence and distant metastasis and poor prognosis. The development mechanism of TNBC is still poorly understood. In clinical practice,for lacking targeted treatment, the TNBC was become the worst molecular subtype.Signal transduction pathways play a very important role in regulation cell growth, proliferation and apoptosis processing. The disordered regulation may lead to cell abnormal growth and continued division. Keep the balance between proteins phosphorylation and dephosphorylation in cells is an important part of signal transduction. In this process, much of researches focus on protein tyrosine kinase (PTKs) and protein tyrosine phosphatase (PTPs). They plays a very important role in protein tyrosine phosphorylation adjustment.Some scholars found the unbalance of intracellular phosphorylation involved in breast cancer development. Namely tyrosine phosphatase activity reduced and/or tyrosine kinase activity enhanced can lead to breast epithelial cells malignant growth, differentiation and proliferation.The epidermal growth factor receptor is the largest kind of tyrosine kinase. The epidermal growth factor receptor family (also known as ErbB receptor family) are composed of four related receptor tyrosine kinase, which are EGFR (HER1/ErbB-1), HER2(ErbB-2/neu), HER3(ErbB-3) and HER4(ErbB-4). By combing to the specific ligand with high affinity, the inactive monomer original receptors in the cell membranes form into homodimers or heterodimers. Thus receptor tyrosine kinase is activated and enables the downstream of signaling pathways, and ultimately regulates of cell proliferation, differentiation process. The excessive activation of epidermal growth factor will lead to cell proliferation signal transmission continuously. Continuous signal transduction to intracellular membrane and the nucleus will lead the cell division, proliferation, invasion, transfer and promoting the tumor angiogenesis, which are related to tumor metastasis and poor prognosis.Studies have found that EGFR overexpresses14%to90%of the breast cancer. Cells with overexpressed EGFR are poorly differentiated, more aggressive, with tendency of early lymph node metastasis, and resisted to endocrine therapy. Also, there are20%to30%of the breast cancer patients with HER-2overexpression or gene amplification. Breast cancer with Her-2high expression have are poor prognosis, with higher rate of distant metastasis and recurrence. At present, in view of the special genetic marker HER-2, anti-tumor molecular targeted therapy by using Trastuzumab in breast cancer with overexpression Her-2has already obtained encouraging results in clinical application.People are making a systematic study on tyrosine kinase, meanwhile researching of tyrosine phosphatase is in progress. The first specific tyrosine phosphatase was found in1980. In the next20years, members of the family PTPs has increased to at least107, the role of tyrosine phosphatase in tumors development has become more and more widely known.Protein tyrosine phosphatase PTPN12(also known as PTP-PEST) was found in human skeletal muscle by Yang using the polymerase chain reaction (PCR) method in1993. The human PTPN12gene is located in chromosome7q11.23. The gen codes the60KD-size protein, which contains510amino acids. In2001, Dominique found PTPN12play a negative role regulation in lymphatic cell activation by inducing Shc, Pyk2, Fak and Cas phosphorylation and deactivation the RAS-MAPK pathways. Later studies have found that PTPN12can control the movement and adhesion of colon cancer, ovarian cancer, and fibroblasts, and thus was thought to potentially regulate the transfer of the tumor cells. In2011, Sun found PTPN12can reduce breast epithelial cell proliferation and transformation. PTPN12was through to inhibit cell proliferation and malignant by negatively control EGFR/her-2centered tyrosine phosphatase pathway. The combination use of multiple-targets tyrosine kinase inhibitors can damage the proliferation and tumorigenic capacity of TNBC cell line. At the same time, a lot of the TNBC cell and tumor are lack of PTPN12expression. In these breast cancer cells, once recovering PTPN12function, the potential of growth and metastatic was greatly damage. Therefore, PTPN12is recognized as a suppressor in triple-negative breast cancer.Objectives:There is no report studying the relationship between PTPN12and breast cancer patients in China. This study is to test the expression of PTPN12in molecular subtype of breast cancer in chinese, and to investigate the proteins potentially interacting with PTPN12, the association between PTPN12and clinicopathologic characteristics as also analyzed. Retrospectively analysis on the relationship between PTPN12expression and overall survival time of breast cancer patients were performed. All of these could set a basis for us to study the role of PTPN12in breast cancer development, and also provide the preliminary theory basis for prognosis judgment and the choice of therapy target.Methods: 1.Eighty-four specimens (biopsy or mastectomy) with complete follow-up data were collected from NanFang Hospital of the NanFang Medical University between2005and2009.A11of them had been confirmed the expression of ER, PR and overexpression of HER-2by immunohistochemical assays.50cases of these were triple negative breast cancers,34cases were non-triple negative breast cancers. Immunohistochemical staining technique was performed to measure the expression of PTPN12, the expression of PTPN12in different molecular subtypes of breast cancer were analysed.2. Immunohistochemical staining technique was performed to measure the expression of EGFR, the expression of EGFR in different molecular subtypes of breast cancer were analysed. The correlations between PTPN12expression and ER、PR、HER-2and EGFR were analyzed.3. Clinicopathologic characteristics of84patients, including age, tumor stage, lymph node status, distant metastasis, clinical stage and information of ER/PR/HER-2expression were recorded. The correlations between PTPN12expression and clinicopathologic characteristics were analyzed.4.Survival analysis was used to analyze the relationship of PTPN12protein expression with breast cancer patients’s overall survival time retrospectively. Cox proportional-hazard analysis was used for univariate and multivariate analysis to explore the effect of variables on breast cancer patients’s overall survival time.Statistical analysisStatistical analysis was done using the SPSS13.0statistical package. The difference of PTPN12protein’s expression rate and density was analyzed by χ2test and Manny-whitney U test respectively. Ranked group data was analyzed by Spearman rank correlation. Logistic regression was performed to analysis the relationship between PTPN12expression and clinical parameters. The relationship between PTPN12expression and each clinicolopathologic parameters with breast cancer patients’ overall survival time was analysed by Kaplan-Meier survival analysis method. Cox proportional hazards model was used to evaluate the independent prognostic variables on overall survival time. All values were determined from two-tailed tests, P<0.05was considered as significant.Results:1.PTPN12protein expressed in cell membrane and cytoplasm. The proportion of different levels of PTPN12expression in TNBC tissues were as follows:"-"42.0%(21/50),"+"26.0%(13/50),"++"28.0%(14/50),"+++"4%(2/50). The proportion of different levels of PTPN12expression in non-TNBC tissues were as follows:"-"20.6%(7/34),"+"23.5(8/34),"++"29.4%(10/34),"+++"26.5%(9/34).The density of PTPN12expression in non-TNBC tissues was significantly higher than that in TNBC tissues. Statistical analysis showed that the negative rate of PTPN12was significantly higher in triple negative breast cancer than that in non-triple negative breast cancer (42.0%vs.20.6%, P=0.041).2. EGFR protein expressed in cell membrane and cytoplasm. The expression of EGFR was significantly higher in TNBC than in non-TNBC (76.0%vs.47.1%,P=0.007).3.There was inverse correlation between EGFR expression and PTPN12(rs=-0.208,p=0.058). PTPN12expression showed significant correlation to human epidermal growth factor receptor-2(HER-2)(rs=-0.25,=0.022).4. Kaplan-Meier analysis showed that lymph node status, clinic stage and PTPN12expression were related to overall survival time of breast cancer patients(P<0.05). Multivariate survival analysis showed that PTPN12was an independent factor effecting breast cancer patients’s overall survival time(P<0.05). While, none independent prognostic factors was found in subgroups of TNBC and non-TNBC cases.Conclusion:1.In this study, We found loss of PTPN12expression occurred more frequently in TNBC than in non-TNBC in chinese. This point was consistent with the conclusion that Sun and his colleagues drew, making us to consider that PTPN12loss is a prevalent phenomenon. This conclusion supported the view that PTPN12was a suppressor in TNBC.2. We found there was negative relationship between expression level of PTPN12protein and EGFR/HER-2proterin. The mutual exclusivity of this two proteins indicated that PTPN12constrained the expression of EGFR/HER-2. This result supported the conclusion that PTPN12negatively regulated EGFR and HER-2at the protein level.Thus, PTPN12may serve as a target for treating breast cancer.3. In this study, patients with positive expression of PTPN12survived longer than patients with negative expression. PTPN12might be an independent prognosis factor in breast cancer.