This discrepancy might be explained by the results of a recent study by Razandi et al[33]; tamoxifen targeted ERβ to induce apoptosis via increasing reactive oxygen species (ROS) in breast-cancer cell lines sensitive to tamoxifen therapy, but it functioned as an agonist to ERβ in resistant cell lines augmenting cell proliferation. This evidence concerns the gene ESR2 and breast carcinoma.