[Estradiol-progesterone interaction in normal and pathological human breast cells]

In most target tissues of the female genital tract, an adequate cell differentiation can be obtained with the successive and synergistic action of estradiol (E2) and progesterone (P), essentially because the progesterone receptor (PR) synthesis implicates the previous action of E2 via its E2 receptor (ER). In normal breast, E2 stimulates the growth of the ductal system whereas the development of acini depends on P secretion. In other words, when E2 plus P are secreted by the ovaries in balanced proportions, the two hormones permit a complete and harmonious development of the mammary gland. The antiestrogenic activity of P is carried out through the decrease of ER resynthesis and stimulation of 17 beta-hydroxysteroid dehydrogenase enzyme activity, which transforms E2 into its less active metabolite estrone (E1) in the target cells. These biochemical events are well documented concerning the endometrium. They have also been observed in normal mammary cells in primary cultures as well as in breast fibroadenomas with high epithelial cellularity. Moreover, data from literature indicate that E2 could be both a direct and indirect factor of cell multiplication in cancerous cell lines. P as well as progestins have the opposite effect. Recent results from this laboratory indicate that E2 and P also have antagonistic effects on the cell multiplication of normal human mammary cells in primary culture. Therefore, the hypothesis that a lack of P during a long period of the female genital like could be a factor in the promotion of breast cancer must be considered.