A Mouse Model Of Spontaneous Triple-negative Breast Cancer

Purposes:1. Clinical and pathological information and outcomes of43triple-negative (TN) breast cancers were compared with those of156non-negative (NTN) breast cancers to investigate the characteristics of human TN breast cancer and the factors influencing its prognosis.2. To investigate biological behavior and immune features of TA2spontaneous breast cancer. Comparative analysis the characteristics of TA2spontaneous breast cancer and human TN breast cancer. Moreover, by analyzed the affect of pregnancy advanced the growth of TA2spontaneous breast cancer, and the relationship between MMTV and TA2spontaneous breast cancer to investigate the mechanism of TA2spontaneous breast cancer.Methods:1.199cases of complete clinical and pathological data in patients undergoing surgery at Tianjin Medical University General Hospital from1997to2004were collected, which were infiltrating ductal breast cancer. The clinical and Pathological factors including age, turnor size, lymphatic node metastasis, treatment, relapse and distant metastasis of TN and NTN cases were compared with person chi-square test. Kaplan-Meier survival analysis was performed to see if there is significant difference in the prognosis between TN and NTN breast cancer.2. Biological behavior, morphological and immune features of33TA2spontaneous breast cancers were observed. H&E staining was used to detect the morphological. Immunohistochemical staining was used to detect ER, PR, HER2, p53, cyclinD, CK5/6、CD31and PCNA expression. The breast cancer cells were inoculated in pregnancy TA2mice to detect the growth of tumor. Electrochemical method was used to detect the estradiol and progesterone in serum. Electron microscope was used to observe the MMTV expression in breast cancer organization. And real time PCR was performed to detect MMTV LTR, ERa and PR mRNA expression.Results:1. In this study,21.6%breast cancers were TN, NTN were78.4%. Middle age of TN and NTN breast cancer were47years and51years, respectively.11.6%TN breast cancers were younger than40years, which were7.7%in NTN breast cancers. Tumor diameter of TN breast cancer was more than2cm, while16.0%of non-triple negative breast cancer has a small tumor. The difference in tumor volume was statistically significant (χ2=8.432, P=0.015).The axillary node-positive percentage in two groups was no statistically significant (χ2=3.815, P=0.148). There were20.5%NTN breast cancer cases in stage I, while most of TN breast cancer patients were in stage Ⅱ or Ⅲ, and the difference was statistically significant. But histological grade was not significant. About4.7%TN breast cancer patients underwent pre-chemotherapy which was significantly more than1.3%in the NTN group, and55.8%TN patients had post-chemotherapy which was44.9%in the NTN group. Both of them were no statistically significant (χ2=1.619, P=0.230;(χ2=1.943, P=0.205).2. During follow-up4.7%of TN cases appeared local recurrence and metastasis, which was1.9%in NTN breast cancer. The two groups were no difference (χ2=1.024, P=0.295).6TN breast cancer patients was likely to metastasize to lung, liver, bone and brain which was significantly more than3.8%in the NTN group (χ2=6.077,P=0.024). Kaplan-Meier survival analysis showed that the overall survival and disease-free survival of TN breast cancer was worst than NTN breast cancer patients (χ2=29.098, P=0.000).3. The structure of TA2spontaneous breast cancer was similar to human invasive breast cancer that is mostly composed of poorly differentiated and small round cell with few cytoplasms and well-developed stroma. Great deals of cells are undergoing mitosis. Necrosis occurred in the centre of the tumor nest. TA2breast cancer is negative for ER, PR and HER2. Some of them expressed p53, cyclinD and PCNA.4. H&E staining confirmed that the morphological of the metastasis tumor cells and primary tumor cells was consistency in mouse breast cancer tissues. The breast cancer cell suspension was subcutaneous injected into the pregnant mice left groin. Tumor size was measured and the tumor growth curve showed breast tumor grew more quickly in the pregnancy group than in control group (t=4.142, P=0.000). Serum level of estrogen and progestin in the pregnant mice increased dramatically (P<0.01respectively), while ER a and PR mRNA in the tumors of mice with spontaneous breast cancer were significantly less than those in the mammary glands (t=12.245,10.933, P=0.000,0.001, respectively). The results of immunohistochemical staining indicated that there was higher PCNA expression in tumors of the pregnancy group than those in the control. That means tumors in the pregnant TA2mice had a high proliferation activity. Moreover, tumor vessels of the pregnancy group were more than that in the virgin group.The EM observation showed MMTV viral particles in the tumor cells. Real-time PCR showed the pregnant mammary land and the intratumoral both were expressed MMTV LTR mRNA higher than normal TA2mouse mammary land, and it was significant difference among the three groups(P<0.01).Conclusions:1. TN breast cancers always occur in young women, especially in premenopausal women. And TN breast cancers have a bigger tumor and a late clinical stage than NTN breast cancers. TN breast cancer tends to metastasize to lung and liver after surgery. The prognosis and life quality of TN breast cancer are poor, and the survival time are short.2. TA2spontaneous breast cancer in the biological behavior, morphological feature and immune characteristic was similar to human TN breast cancer. TA2mouse is a good animal model for human TN breast cancer research hence.3. TA2spontaneous breast cancer is closely related to the MMTV, which can integrated into the mouse mammary tissue genome to activate the oncogene, induced breast cancer in mice. Pregnancy can promote the growth and metastasis of breast cancer in mice. Estradiol and progesterone secretion is not only promoting the growth of breast cancer, but also have synergy with MMTV. They have an important value in research the mechanisms of TA2mice breast cancer.