Tamoxifen acts as a GPER agonist, induces aromatase expression, and contributes to resistance to endocrine therapy in breast cancer (Meijer et al., 2006; van Agthoven et al., 2009; Ignatov et al., 2011; Catalano et al., 2014; Yin et al., 2017; Molina et al., 2020; Yu et al., 2020). The gene discussed is GPER1; the disease is breast cancer.