Effects of estradiol and medroxyprogesterone acetate on morphology, proliferation and apoptosis of human breast tissue in organ cultures

Background: Human breast tissue undergoes phases of proliferation, differentiation and regression regulated by changes of the levels of circulating sex hormones during the menstrual cycle or aging. Ovarian hormones also likely play a key role in the etiology and biology of breast cancer. Reports concerning the proliferative effects of steroid hormones on the normal epithelium of human breast have been conflicting. Some studies have shown that steroid hormones may predispose breast epithelial cells to malignant changes by stimulating their proliferation, which is known to be regulated tightly by stromal cells. The aim of this study was to investigate the effects of 17 beta-estradiol and medroxyprogesterone acetate on proliferation, apoptosis, expression of differentiation markers and steroid hormone receptors in breast epithelium using an in vitro model of freshly isolated human breast tissue, in which a proper interaction of breast epithelium and stroma has been maintained. Methods: Human breast tissues were obtained from women undergoing surgery for breast tumours. Peritumoral tissues were excised and explants were cultured for 3 weeks in medium supplemented with E-2 or MPA or with E-2+ MPA. Endpoints included histopathological, histomorphometric and immunohistochemical assessment of the breast explants. Results: Culture of breast explants for 14 or 21 days with steroid hormones increased proliferative activity and the thickness of acinar and ductal epithelium. E-2-treatment led to hyperplastic epithelial morphology, MPA to hypersecretory single-layered epithelium and E-2+ MPA to multilayered but organised epithelium. The proliferative response to E-2 in comparison to control ( p < 0.001) was more pronounced than to MPA ( p < 0.05) or E-2+ MPA ( p < 0.05) at 7 and 14 days for Ki-67 and PCNA. E-2 treatment also decreased the proportion of apoptotic cells after 7 ( p < 0.01) and 14 ( p < 0.01) days. In addition, the relative number of ER alpha, ER beta and PR positive epithelial cells was decreased by all hormonal treatments. Conclusion: Organ culture system provides a model for studying the direct effects of steroid hormones and their analogues on postmenopausal human breast tissue.