ESR1 and neoplasm: Since we previously demonstrated that this E2-induced ER-negative tumor growth is dependent on the expression of ERα in endothelial cells, promoting a normalized angiogenesis and tumor growth 10, the effect of tamoxifen on vascular density and vessel normalization was evaluated using a double CD31 and pericyte marker α-smooth muscle actin (αSMA) immunostaining (representative pictures in Figure 2E).