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Objective: Our purpose was to compare the effects of tibolone, continuous combined hormone replacement therapy, and placebo on mammographic breast density., Study Design: A prospective, randomized, double-blind placebo-controlled study was performed. A total of 166 postmenopausal women were equally randomized to receive tibolone 2.5 mg, estradiol 2 mg/norethisterone acetate 1 mg (E(2)/NETA), or placebo. Mammograms were performed at baseline and after 6 months of treatment. Mammographic density was quantified according to the Wolfe classification and by the percentage area of the breast that had a dense pattern., Results: An increase in mammographic density was much more common among women receiving continuous combined hormone replacement therapy (46%-50%) than among those receiving tibolone (2%-6%) and placebo (0%) treatment. The difference between E(2)/NETA and placebo was highly significant (P <.001). Treatment with tibolone did not differ from that with placebo. The relative risk of an increase in breast density for E(2)/NETA versus tibolone was found to be 8.3 (95% CI 2.7-25.0)., Conclusion: An increase in mammographic density should be regarded as an unwanted side effect of hormone replacement therapy. In contrast to estrogen/progestogen treatment, tibolone seems to exert little stimulation of breast tissue.

Objective: Our purpose was to investigate the effects of various hormone replacement regimens on mammographic breast density., Study Design: Mammographic density was recorded in women participating in a population-based screening program. All women were nonusers of hormone replacement therapy at first mammogram and thereafter reported continuous use of the same treatment: estrogen alone (n = 50) or estrogen in cyclic (n = 75) or continuous (n = 50) combination with progestogen. Mammographic density was quantified according to the Wolfe classification., Results: An increase in mammographic density was much more common among women receiving continuous combination hormone replacement therapy (52%) than among those receiving cyclic (13%) and estrogen-only (18%) treatment. The increase in density was apparent already at first visit after the start of hormone replacement therapy. There was little change in mammographic status during long-term follow-up., Conclusion: Regimens of hormone replacement therapy were shown to have different effects on the normal breast. There is an urgent need to clarify the biologic nature and significance of a change in mammographic density during treatment and, in particular, its relation to symptoms and breast cancer risk.

Objective: Our objective was to assess proliferation in normal breast epithelial cells from healthy women during the follicular and luteal phases of the menstrual cycle., Study Design: We analyzed the proliferation marker Ki-67/MIB-1 by immunocytochemical methods in breast epithelial cells procured through fine needle aspiration biopsy from 47 healthy volunteers. Differences were assessed by Wilcoxon rank sum tests, and correlations were determined by Spearman's rank correlation coefficient., Results: The proportion of KI-67/MIB-1-positive cells was higher in the luteal phase (2.04%) than in the follicular phase (1.66%). The values in women aged < 35 years were 2.29% and 1.13%, respectively (p = 0.003). In ovulating women with two aspirates during the same menstrual cycle the percentage of proliferating cells increased from the follicular phase (1.3%) to the luteal phase (2.4%) (p < 0.04). Proliferation was positively correlated with serum progesterone levels the day of aspiration (r = 0.34, p < 0.05)., Conclusion: The fine needle aspiration biopsy technique is a valuable tool for in vivo studies of cell proliferation in the normal breast. Data clearly suggest a proliferative action of progesterone.

Objective: Our objective was to analyze the presence of estrogen and progesterone receptors in breast epithelial cells from healthy women during the follicular and luteal phase of the menstrual cycle., Study Design: We analyzed estrogen receptor and progesterone receptor variations in breast epithelial cells procured through fine-needle aspiration biopsy from 42 healthy volunteers during the menstrual cycle using immunocytochemical receptor analysis. Differences were assessed by chi 2 test and the Wilcoxon rank sum tests., Results: Estrogen receptor was detected more often in women aspirated in the follicular (68%) than in the luteal (32%) phase (p < 0.001); progesterone receptor was detected in around 80% in both phases. In ovulating women who were aspirated twice during the same menstrual cycle the proportion of estrogen receptor-positive cells was reduced from 20% to 4% (p < 0.02); the progesterone receptor values were 17% and 24%., Conclusion: Our data indicate an important difference in progesterone receptor variation in the breast as compared with the endometrium.