Aromatase and steroid sulfatase inhibitors, SERDs, and SERMs synthetically derived from natural hormones are of great interest for the development of new breast cancer treatment regimens, especially for metastatic forms of the disease (Singer et al., 2006; Scherbakov et al., 2013; Secky et al., 2013; Boer, 2017; Kaklamani and Gradishar, 2017). Fulvestrant is an estrogen receptor degrader that binds with high selectivity to target cells, causes their degradation, resulting in the complete inhibition of the estrogen-mediated growth of breast cancer cells (Nathan and Schmid, 2017). First approved in the US in 2002, fulvestrant is not associated with tamoxifen-like agonist side effects, is not cross-resistant to tamoxifen or exemestane, and produces very high response rates in breast cancer patients. A combination of fulvestrant with other drugs seems to be very promising. In this regards, the combination of anastrozole and fulvestrant is superior to anastrozole alone or sequential anastrozole and fulvestrant for the treatment of ERα-positive metastatic breast cancer (Mehta et al., 2012).