Study on mouse model of triple-negative breast cancer: association between higher parity and triple-negative breast cancer

To investigate the association between high parity and triple-negative breast cancer (TNBC), and explore the etiologic mechanisms of TNBC in Tientsin Albinao 2 (TA2) mice model. After the TA2 mice model with high parity and TNBC had been established, the cell proliferation and apoptosis were detected by immunohistochemical and TUNEL staining in mammary epithelia from different conditions, which included non-pregnancy, low and high gravidity in pregnancy, and carcinogenesis. Apoptotic signaling was analyzed by measuring bcl-2, bax, caspase-3, and caspase-9 expression using immunohistochemistry (IHC), western blot, and real-time PCR technique. Estrogen receptor α (ERα) and progesterone receptor (PR) were determined by immunohistochemical staining and real-time PCR. Both proliferation and apoptosis in mammary epithelia changed with the increasing of parity. Immunohistochemistry revealed increased cell proliferation and apoptosis were related with upregulation of ERα, PR, bcl-2, bax, caspase-3, and caspase-9 expression, especially during the fourth pregnancy. Mammary gland in the fourth pregnancy stage was the closest to precancerous. In precancerous mammary gland, cell proliferation rate was much higher than apoptosis rate. High parity could increase the ovarian hormones level and alter ovarian hormone receptor levels in TA2 mice, and their sensitivity to ovarian hormones result in the imbalance between cell proliferation and apoptosis in precancerous mammary epithelial cells.