In the present study the A P

In the present study, the A/P ratio in the MCF-7 cell line was significantly increased by the combination of 1 nM E2 and progestogens, except P4, as well as by10 nM E2 combined with NET. The similar findings were also noted by several reports [16], [17], [18], [19], [20] in which progestogens combined with E2 significantly increased the cell death to proliferation ratio, in comparison with using E2 alone. In addition, the PRA/PRB ratio was significantly reduced through combined use of 1 nM E2 with progestogens, except P4, and by the combination of 10 nM E2 and NET as well. The PRA/PRB ratio was inversely correlated with the changes of the A/P ratio. This reveals that the response of MCF-7 Discussion to the effects of combined E2 and progestin may be modulated via alterations in the ratio of PR-A and B expression. Hopp et al [21] also found that the regulated expression of PRA and B is critical to the mammary gland's response to progesterone. In addition, the effects of P4 plus E2 on ERs and PRs were similar to using E2 alone, but were different from using synthetic progesterones plus E2. Because the combination of E2 and P4 maintained the normal proliferation rate like the control group did, whether progesterone induces other transcriptional regulators to mediate the antiapoptosis of E2 or not should be considered. A French cohort study reported that micronized progesterone or didrogesterone used with oral or percutaneous estradiol showed no increase or decrease in the risk of breast cancer compared to synthetic progestins for at least 4 years of treatment [22] and even after 8 years [23]. Although the results of the present study, except E2 plus P4, were completely opposite to those of the French cohort study, it demonstrates that various progestogens have different effects on breast cells, as well as on the expression of ERs and PRs. Significantly increased expression of ERβ and PRB was noted in E2 combined with MPA or NET, whereas a significant increase of ERα expression and decrease of PRB and/or PRA in the E2 combined with P4 or CPA was also noted. Because the major difference of these four progestogens in regards to biologic activity is the strong androgenic effects of MPA and NET and glucocorticoid effects of MPA and CPA, evident when compared with P4, further evaluation is needed to determine whether the androgen and glucocorticoid receptors also play important roles as additional cofactors on the expression of ERs and PRs, as well as on the effects of breast cell growth. In this decade, although there have been many studies focusing on the effects of different progestogens plus E2 on breast cancer cell growth, the major differences in the present study were the concentrations of progestogens and E2 (Table 1) and the cell preparation. Because our goal was to examine the effects of E2, with or without progestogens commonly used for HT, on breast cells, breast cells were cultured by serum deprivation and growth factors withdrawal to mimic an aging system. The clinically relevant blood concentrations of E2 for achieved HT range 50–200 pg/mL, equivalent to a concentration of 0.01–0.1 nM [20]. However, it is well recognized that estrogens are synthesized in the breast tissue, and especially in tumor tissue, at concentrations that are remarkably higher than blood levels achieved under HT [24]. In addition, the clinically relevant blood concentrations of progestogens in this study are in the region of 10 nM progesterone when administered in a dosage of 200 mg/day [25], and in the range of 4–10 nM for MPA [26] and around 10 nM for NET [27]. Thus, 10 nM progestogens and higher concentration of 1 nM and 10 nM E2 were used in this experiment. Table 1 reveals that most of the other studies demonstrate similar results with higher pharmacological doses of progestogens. In addition, there are few data available to evaluate the effects of progestogens (especially CPA) plus E2 on breast cancer cell growth and the expression of sex steroid receptor subtypes simultaneously like the present study.