ESR1 and breast cancer: The 20 mg/kg dose afforded a peak plasma concentration of over 1000 ng/mL, or 1.6 μM, a level that far exceeds the therapeutically effective concentration of a potent SERD with low nanomolar IC50 values in endocrine sensitive breast cancer cells, and a level that is also significantly higher than its IC50 value in ER mutant breast cancer cells.