[Effects of progesterone and progestational hormones on the mammary gland].

The growth of the mammary gland during the active genital period depends on a delicate balance between the action of the two major female sex steroid hormones, estradiol and progesterone. The regulation of growth and maturation of the gland primarily depends on the combined action of estradiol and progesterone. Breast epithelial proliferation is maximal during the luteal phase of the menstrual cycle. While estrogen appears to be the major impetus to the proliferation of mammary cells, the effect of progestin is subject to debate. Progestins have either a positive, modest or no growth effect or may even inhibit growth. Progestins could stimulate the development of malignant cells in contrast to normal or non-malignant cells. It is difficult to extrapolate in vitro results to the human breast. There is presently no direct evidence that progestins regulate the concentration of estrogen receptors (ER) in normal breasts. Furthermore, it is possible that each type of progestin may have different effects. Most studies suggest that progestins are effective in the treatment of premenstrual syndrome and benign breast disease. The therapeutic basis for the use of progestins is the suppression of pituitary-ovarian function the reduction of the effect of estrogen on breast tissues. Whether progestins give protection against breast cancer is less clear. If they do, the mechanism is not the same as that of the endometrium [down-regulation of ER, increase of 17 beta-hydroxysteroid dehydrogenase activity (E2DH)]. High doses of oral synthetic progestins are effective in the treatment of breast cancer.(ABSTRACT TRUNCATED AT 250 WORDS)