Activated ERK1/2 and phosphorylated oestrogen receptor α are associated with improved breast cancer survival in women treated with tamoxifen

The aim of this study was to investigate the expression of activated (phosphorylated) ERK1/2, oestrogen receptor α phosphorylated at S118 (ERαS118), and HER2 in primary breast cancer, and to make correlations with the outcome of tamoxifen therapy. We performed immunohistochemical analysis to determine the expression of HER2, ERαS118, and activated ERK1/2 in tumours obtained from 279 women with primary breast cancer. HER2 status was also estimated by fluorescence in situ hybridisation. We identified 108 women with ERα-positive tumours who had received adjuvant tamoxifen. Activated ERK1/2 (pERK1/2) and ERαS118 were found to be associated with each other and with other factors correlated with good prognosis. HER2 was inversely associated with pERK1/2. Positive staining for pERK1/2 (particularly intense staining) indicated better relapse-free survival (P = 0.05) and a trend towards better breast cancer-corrected survival in women treated with tamoxifen. To conclude, this study shows that activated ERK1/2 and ERαS118 are associated with improved survival. The poorer outcome in HER2-positive women who receive adjuvant tamoxifen cannot be explained by the crosstalk between HER2 and ERαS118 via activated ERK1/2 alone.