Breast cancer is the most common cancer in women worldwide, with more than 1.5 million new cases recorded every year; it is also the fifth highest cause of cancer death (Nathan and Schmid, 2017). Estrogens are steroid hormones that play a critical role in the regulation of growth, differentiation, and metabolism of mammary cells, including malignant cells. Due to the ability of estrogens to significantly stimulate the growth of mammary cells, these hormones are involved in the progression of breast cancer. For more than 40 years, the antiestrogen tamoxifen (ICI 46474) is considered as the absolute leader in the endocrine therapy of hormone-dependent breast cancers (Jameera Begam et al., 2017). Tamoxifen belongs to selective estrogen receptor modulators (SERMs) (Cosman and Lindsay, 1999; Jameera Begam et al., 2017), which, in certain circumstances, perform the role of estrogen agonists or antagonists and modulate the effect of hormones in the target cells; otherwise, SERMs are also called estrogen agonists/antagonists. Due to convenient dosage forms for oral use, high efficiency, and low cost of the prolonged course of therapy, tamoxifen is considered as the “gold standard” for the treatment of patients with ERα-positive breast cancer. On the other hand, the effectiveness of tamoxifen may be limited by the development of resistance, an increased risk of endometrial cancer, and individual drug intolerance (Scherbakov et al., 2006; Ali et al., 2016; Traboulsi et al., 2017). This is why the development of novel classes of agents that effectively inhibit the growth of ERα-positive tumors and have no severe side effects is a challenge (Tryfonidis et al., 2016).