Different cell activities in breast cancer based on different estrogen receptor-alpha(+)/estrogen receptor-alpha(-) ratios.

e12004 Background: Estrogen receptor-alpha (ERα) is implicated in breast cancer progression. Although tamoxifen and aromatase inhibitors have been widely used to treat ERα-positive breast cancer, the least favorable ERα(+)/ERα(-) expression ratio in the tumor microenvironment and its influence on tumor activity remain poorly understood. We examined different ERα(+)/ERα(-) ratios in an MDA-MB-231 model to identify the least favorable ERα(+)/ERα(-) ratio. Methods: ERα stable transfectants were created in the MDA-MB-231 ER(-) cell line, and the MCF-7 ER(+) cell line was used as a control. Transfected MDA-MB-231 ER(+) and wild-type MDA-MB-231 ER(-) cells were mixed and co-cultured at 100%, 70%, 40%, 20%, and 0% ratios. Migration and invasion abilities of the different cell ratios were evaluated in vitro. Type 2 macrophage transformation; BRCA1 and Her2 expression; and VEGF and TNF-α expression in vivo were measured, and bone and lung metastasis were examined in vivo. Results: The results of transwellassays with fluorescence staining were 249±6, 404±28, 430±25, 401±25, and 361±20 cells for the different mixing ratios and 350±10 cells for the control, respectively (high to low), and wound healing tests with quantitative analysis showed the highest migration rate (84%±5) was for the 40% ratio after 48 h of co-culture. The flow cytometry results for the F4/80(+)/Ly6c(+)proportions were 5.0%±0.56, 7.7%±0.5, 7.2%±0.49, 6.2%±0.57 and 4.9%±0.69 for the different ratios and 4.2%±0.46 for the control, respectively. Immunohistochemical staining and western blotting indicated that 70% ratio had the highest VEGR and TNF-α and BRCA1 and Her2 expression levels in vivo. Lung and bone metastasis were observed in the 70% group. Conclusions: ERα(+)/ERα(-) ratios of 40% in vitro and 70% in vivo serve as critical indicators of cell activity and cytokine expression. Our results suggest that breast cancer cell activity does not exhibit a linear relationship with ERα-positive expression, which indicates that ER status requires multiple checks during tamoxifen or aromatase inhibitor treatment. These results indicate a new therapeutic strategy for preventing ER-positive breast cancer.