['The progestogen nomegestrol acetate (NOMAC), a 17α-hydroxy-nor-progesterone derivative (LUTENYL®) is largely used as an oral contraceptive and to treat menopausal complaints. In previous studies, we demonstrated that NOMAC is an anti-sulfatase agent in MCF-7 and T-47D breast cancer cells. In this study, we explore the effect of NOMAC on aromatase activity in a stable aromatase-expressing human breast cancer cell line: MCF-7aro.', 'Cells were incubated with physiological concentrations of androgen substrates [3H]-testosterone or [3H]-androstenedione (5×10-9\xa0mol/L) alone, or in the presence of NOMAC (5×10-5\xa0mol/L-5×10-8\xa0mol/L) for 24\xa0h at 37°C. [3H]-Estradiol (E2), [3H]-estrone (E1), [3H]-testosterone and [3H]-androstenedione were characterized by thin layer chromatography and quantified using the corresponding standard.', 'Aromatase activity levels are high in MCF-7aro cells because the [3H]-E2 concentration after incubation of [3H]-testosterone was 5.8±0.31\xa0pmol/mg DNA in non-treated cells. At concentrations of 5×10-5\xa0mol/L, 5×10-6\xa0mol/L and 5×10-7\xa0mol/L NOMAC significantly inhibits this conversion by 49.7%, 29.9% and 18.1%, respectively. After [3H]-androstenedione incubation, similar inhibition levels were observed with NOMAC for [3H]-E1 formation; whereas, inhibition of [3H]-E2 production, which implicates 17β-hydroxysteroid dehydrogenase activity in this pathway, is greater because NOMAC also inhibits this enzyme.'] Is nomegestrol acetate an anti-aromatase agent in human MCF-7aro breast cancer cells?