CYP19A1 and breast cancer: The in vitro assays comprised 3 cell-based test systems expressing aromatase: a reconstituted lysate from yeast overexpressing human aromatase (CypExpress); an MCF7 human breast cancer cell line engineered to overexpress aromatase (MCF7arom) (12); and a human placental cell line, which endogenously expresses aromatase (JEG3).