ESR1 and breast cancer: Particularly of relevance to the current study, the C. subternata Vogel extract, SM6Met, was shown in several studies to possess phytoestrogenic activity, to display ERα antagonism and ERβ agonism, to antagonize estrogen-induced proliferation in ER+ BC cells (Mfenyana et al., 2008; Louw et al., 2013; Visser et al., 2013; Mortimer et al., 2015; van Dyk, 2018) and to ameliorate BC in rats (Visser et al., 2016; Oyenihi et al., 2018).