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PubMed1991

The effect of progestin on factors influencing growth and invasion of endometrial carcinoma.

Progesterone (P) and progestins play an important role in the control of endometrial growth. We have investigated P and progestin effects on endometrial estrogen extraction, on basement membrane (BM) synthesis and on the presence of the epidermal growth factor receptor (EGFr) in normal and pathologic endometrium. E2 uptake, evaluated in human isolated perfused uteri is significantly decreased by P. BMs investigated using immunohistochemistry, with antisera to collagen IV and laminin, were found around stromal cells only in the luteal phase or during P or progestin administration. Glandular BM, discontinuous in hyperplastic and carcinomatous endometria, were restored to integrity only in typical hyperplasia after therapy with progestin. Endometrial EGFr is modified by P: revelation of this antigen is increased in proliferative phase and decreased in secretory phase. Similarly this molecule was present in hyperplastic and carcinomatous endometria. Only in benign hyperplasia did we observe no staining for the same antigen after progestinic therapy. These data suggest that P or progestins may also have an indirect influence through mechanisms such as estrogen uptake and tissue factor activity with important differences between normal and pathologic endometrium.

Adult↗

PubMed1998

Mechanisms of cyclin-dependent kinase inactivation by progestins.

The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. In breast cancer cells the predominant effect of synthetic progestins is long-term growth inhibition and arrest in G1 phase. Progestin-mediated growth arrest of T-47D breast cancer cells was preceded by inhibition of cyclin D1-Cdk4, cyclin D3-Cdk4, and cyclin E-Cdk2 kinase activities in vitro and reduced phosphorylation of pRB and p107. This was accompanied by decreases in the expression of cyclins D1, D3, and E, decreased abundance of cyclin D1- and cyclin D3-Cdk4 complexes, increased association of the cyclin-dependent kinase (CDK) inhibitor p27 with the remaining Cdk4 complexes, and changes in the molecular masses and compositions of cyclin E complexes. In control cells cyclin E eluted from Superdex 200 as two peaks of approximately 120 and approximately 200 kDa, with the 120-kDa peak displaying greater cyclin E-associated kinase activity. Following progestin treatment, almost all of the cyclin E was in the 200-kDa, low-activity form, which was associated with the CDK inhibitors p21 and p27; this change preceded the inhibition of cell cycle progression. These data suggest preferential formation of this higher-molecular-weight, CDK inhibitor-bound form and a reduced number of cyclin E-Cdk2 complexes as mechanisms for the decreased cyclin E-associated kinase activity following progestin treatment. Ectopic expression of cyclin D1 in progestin-inhibited cells led to the reappearance of the 120-kDa active form of cyclin E-Cdk2 preceding the resumption of cell cycle progression. Thus, decreased cyclin expression and consequent increased CDK inhibitor association are likely to mediate the decreases in CDK activity accompanying progestin-mediated growth inhibition.

Breast Neoplasms↗

PubMed2002

Progestin and G protein-coupled receptor 30 inhibit mitogen-activated protein kinase activity in MCF-7 breast cancer cells.

We have previously shown that the G protein-coupled receptor (GPR)30 is critical for progestin-induced growth inhibition. In this study, we addressed signal transduction pathways involved in progestin-mediated signaling. Progestin could not provide any additional growth inhibitory effect to MCF-7 cells treated with specific MAPK kinase inhibitors, PD98059 and U0126. Medroxyprogesteroneacetate (MPA) induced a late (22-23 h) decrease in ERK-1 and -2 activities verified by immunoblotting and kinase assay. The inactivation was abrogated by antiprogestin. Transient expression of GPR30 decreased ERK-1 and -2 activity; and in the cells in which GPR30 expression was decreased by the antisense, ERK activities were increased. The antisense-expressing cells were able to significantly resist the growth-inhibitory effect of the MAPK kinase inhibitors PD98059 and U0126 but not that of other factors tested. Interestingly, the decrease of ERK activity induced by MPA was abrogated by GPR30 antisense. Collectively, these results show that MAPK activity is inhibited by progestin and GPR30 and suggest that progestin-induced ERK inactivation is mediated through GPR30. Coupled with our previous findings, the data imply that up-regulation of GPR30 by progestin leads to ERK-1 and -2 inactivation associated with MPA-induced growth inhibition.

Breast Neoplasms↗

PubMed2005

Proliferation of endothelial and tumor epithelial cells by progestin-induced vascular endothelial growth factor from human breast cancer cells: paracrine and autocrine effects.

Angiogenesis, the formation of new blood vessels, is essential for tumor expansion, and vascular endothelial growth factor (VEGF) is one of the most potent angiogenic growth factors known. We have previously shown that natural and synthetic progestins, including those used in hormone replacement therapy and oral contraception, induce the synthesis and secretion of VEGF in a subset of human breast cancer cells in a progesterone receptor-dependent manner. We now report that conditioned medium from progestin-treated breast tumor cells can induce the proliferation of endothelial cells in a paracrine manner and induce the proliferation of tumor epithelial cells in a paracrine and an autocrine manner. The use of an anti-VEGF antibody and SU-1498, an inhibitor of VEGF receptor-2 (VEGFR-2 or flk/kdr) tyrosine kinase activity, demonstrated that these effects involve interactions between VEGF and VEGFR-2. Also, blockage of progestin-induced VEGF by the antiprogestin RU-486 (mifepristone) eliminated VEGF-induced proliferative effects. The ability of VEGF to increase the proliferation of endothelial cells and tumor cells, including those that do not release VEGF in response to progestins, suggests that these effects are mediated by amplification of the progestin signal, which culminates in angiogenesis and tumor growth. These novel findings suggest that targeting the release of VEGF from tumor epithelial cells as well as blocking interactions between VEGF and VEGFR-2 on both endothelial and tumor epithelial cells may facilitate the development of new antiangiogenic therapies for progestin-dependent breast tumors. Furthermore, these data indicate that it would be useful to develop selective progesterone receptor modulators that prevent the release of angiogenic growth factors from breast cancer cells.

Breast Neoplasms↗

PubMed1979

Antiestrogen inhibits the induction of progestin receptors by estradiol in the hypothalamus-preoptic area and pituitary.

Estradiol treatment of ovariectomized-adrenalectomized rats produced an increase in cytosol progestin binding in the hypothalamus-preoptic area (HPOA), pituitary, and uterus. In the HPOA and pituitary, this induction of progestin receptors by estradiol was inhibited by the antiestrogen CI-628 under a variety of dose and time conditions. In the uterus, inhibition of the full effect of estradiol on progestin binding was observed after 3 days of injection of antiestrogen and estradiol. In the absence of estradiol, the antiestrogen produced a slight induction of progestin receptors in the HPOA and pituitary and a substantial induction of progestin receptors in the uterus. The results suggest that the induction of progestin receptors could be a key intermediate step in some behavioral and neuroendocrine actions of estradiol.

Animals↗

PubMed1981

Nuclear progestin receptors in human uterus.

The characteristics and transfer of human uterine progestin receptors from cytosol to nucleus were studied in a cell-free system using [3H]progesterone ([3H]P), [3H]norethindrone ([3H]NET), and [3H]norethindrone acetate ([3H]NETA) as progestin receptor tags. Nuclear receptor binding was observed only in the presence of uterine cytosol. Various prior treatments of uterine cytosol, including warming to 20 C, increasing the salt concentration to 150 mM KCl, or dilution of the cytosol protein concentration to 3 mg/ml, increased the affinity of the receptor for the cell nucleus and thus, facilitated more translocation. However, there was no detectable difference in the receptor sedimentation value after activation. The binding of salt-extractable (400 mM KCl) nuclear sites to [3H]P, [3H]NET, and [3H]NETA was characterized by distinct commonality in their physiochemical properties, as indexed by their coelution during gel chromatography (mol wt, 72,000), their similar sedimentation rates (4.2S), and their similar isoelectric profiles (isoelectric pH 5.3--5.6). The concentrations of specific binding sites were similar for the different 3H-labeled progestins used. However, in general, the number of binding sites was higher (3780--4480 molecules/cell) in proliferative phase tissues and significantly lower (1790--1920 molecules/cell) in secretory phase tissues. Furthermore, nuclear binding was progestin specific and of high affinity (Kd of NET, similar to or approximately 0.7--0.8 nM; Kd of P, similar to or approximately 0.9--1.2 nM; Kd of NETA, similar to or approximately 6.7--7.1 nM). Despite the similarities in the molecular properties, the nuclear bindings of NET and NETA could be distinguished from that of P by their lower dissociation rates (t 1/2 of NET, similar to or approximately 6.3 h; t 1/2 of NETA, similar to or approximately 5.5 h; t 1/2 of P, similar to or approximately 1.2 h). Moreover, NET and NETA, unlike P, did not bind to corticosteroid-binding globulin. These observations indicate that the various progestins mediate their action via a common receptor, which translocates from cytosol to nucleus. Further, because of the distinct advantages, NET could be conveniently used as a receptor tag to evaluate the progestin receptor.

Cell Nucleus↗

PubMed1983

Progestin-like effects of danazol on rabbit uterus.

The action of danazol on cytosol and nuclear progestin and estrogen receptor concentrations and on the induction of uteroglobin synthesis were studied in the rabbit uterus in vivo. In addition, the relative binding affinity of danazol for the uterine progestin receptor was measured in vitro. Administration of increasing doses of danazol (10, 50, or 100 mg/kg BW daily) for 5 days to adult rabbits tended to decrease the concentrations of cytosol and nuclear progestin and estrogen receptors, whereas the uterine uteroglobin content increased with increasing doses of danazol. Progesterone (1 mg/kg BW daily) caused changes which were greater than those caused by the largest dose of danazol. Danazol was found to bind to the uterine progestin receptor in vitro with an affinity approximately 3.3% of that of progesterone. These findings suggest that danazol has a profound progestin-like activity in the rabbit uterus which may be mediated through binding to cytosol progestin receptors.

Animals↗

PubMed2001

Up-regulation of p27Kip1 by progestins is involved in the growth suppression of the normal and malignant human endometrial glandular cells.

Progestins are known to suppress the growth of normal human endometrial glands and endometrial carcinomas possessing PRs. To elucidate the molecular mechanisms of progestin-induced growth inhibition, the expression and functional involvement of p27Kip1 (p27), a cyclin-dependent-kinase inhibitor, was investigated using cultured normal endometrial glandular cells and endometrial carcinoma cell lines (Ishikawa; PR-positive, KLE; PR-negative). Growth of the normal endometrial glandular cells and Ishikawa cells was suppressed by treatment with progesterone and medroxyprogesterone acetate, respectively, in association with an increase in p27 protein expression. Immunoprecipitation revealed that progestins accelerated the complex formation of p27 and cdk2 in both types of cells. However, treatment with progestins did not show any marked alterations in the mRNA expression of p27 in either normal glandular cells or Ishikawa cells. On the other hand, p27 protein degradation experiments indicated that treatment with progesterone and medroxyprogesterone acetate prolonged the degradation time of the normal endometrial glandular cells and Ishikawa cells, respectively. Forced expression of the p27 protein using a p27 expression plasmid reduced the growth activity of normal endometrial glandular cells. These findings suggest that p27 is functionally involved in progestin-induced growth suppression of normal and malignant endometrial epithelial cells and that up-regulation of the p27 protein by progestins possibly occurs via posttranslational mechanisms.

Cell Cycle Proteins↗

PubMed2002

Hepatocyte growth factor is required for progestin-induced epithelial cell proliferation and alveolar-like morphogenesis in serum-free culture of normal mammary epithelial cells.

The steroid hormones, estrogen and progesterone, are required for mammary epithelial cell proliferation and alveolar morphogenesis in vivo. We have developed a minimally supplemented, serum-free medium, collagen gel primary mammary culture system to determine the mechanism of progestin-induced proliferation and alveolar morphogenesis. In epithelial cells cultured alone, treatment with progestin (R5020) alone produced a lumen within the epithelial organoids, but did not stimulate epithelial cell proliferation. The formation of lumens was associated with increased apoptosis, targeted within the organoids. We have previously reported that in our culture system hepatocyte growth factor (HGF) increases epithelial cell proliferation and induces a tubulo-ductal morphological response. In the present report we show that treatment with HGF and progestin (R5020) further increases epithelial proliferation above that with HGF alone and also produces an alveolar-like morphology similar to that observed in vivo in response to progestin treatment. To the best of our knowledge this is the first in vitro demonstration of both progestin-induced proliferation and alveolar-like morphogenesis of normal nonpregnant mouse mammary epithelial cells in vitro. These results suggest that HGF may play a crucial role in progestin-induced proliferation and morphogenesis in vivo.

Animals↗

PubMed1990

Effects of progestins and menstrual cycle on fatty acid synthetase and progesterone receptor in human mammary glands.

Fatty acid synthetase (FAS) is induced by progestins in human breast cancer cell lines. To study its regulation in normal mammary glands, the FAS level was estimated by immunohistochemistry, using the biotin-streptavidin method, in ducts and lobules of normal tissues adjacent to nonproliferative benign breast lesions collected by biopsy. Rabbit polyclonal antibodies to human FAS specifically recognized the 250-kDa FAS from MCF7 cells, as shown by Western immunoblotting. An excess of purified FAS totally switched off FAS immunostaining of R5020-treated MCF7 cells, demonstrating the validity of FAS immunocytochemical detection. FAS labeling was quantified using a computer-aided image analyzer (SAMBA 2005) in 18 patients receiving progestin therapy from the 15th to the 25th day of the menstrual cycle and 26 untreated patients. In the 2 groups, FAS staining, absent of fibroblasts, was observed in the cytoplasm of epithelial cells. It was higher in lobules than in ducts and increased significantly from the follicular to the luteal phase in both structures. Progestin treatment increased FAS expression in both structures. Using monoclonal antibodies, progesterone receptor expression was measured in frozen serial sections. In patients receiving progestin treatment, the progesterone receptor level increased from the beginning of the cycle to day 14 and then decreased during the second part of the menstrual cycle, probably down-regulated by progestin, indicating a regulation similar to that in the endometrium. We conclude that FAS is induced by progestins in the ducts and lobules of human normal mammary glands as it is in human breast cancer cells. FAS may, therefore, be useful for studying the effect of progesterone in normal human mammary glands.

Breast↗

PubMed1990

Progestin regulation of estrogen receptor messenger RNA in human breast cancer cells.

Progestin antagonism of estrogen action is thought to be due, at least in part, to progestin down-regulation of the estrogen receptor (ER). The molecular mechanisms subserving this effect, and the functional consequences in terms of target cell sensitivity to estrogens, are poorly understood. The present study was undertaken to address these issues with particular emphasis on progestin regulation of ER gene expression at the mRNA level. The T-47D human breast cancer cell line was treated with the synthetic progestin, ORG 2058, and the resultant changes in ER mRNA and ER levels determined by Northern analysis and radioligand binding, respectively. Treatment of T-47D cells with ORG 2058 resulted in rapid down-regulation of ER mRNA levels to a nadir of 35-40% of control by 6 h. This fall in ER mRNA levels was accompanied by a slower but more sustained fall in ER binding to a nadir of 20% of control at 24 h. Between 12 and 24 h ER mRNA levels recovered partially while ER ligand binding continued to fall. At 48 h both ER mRNA and ER concentrations remained depressed, although the latter to a greater extent. ER mRNA half-life was determined by [3H]uridine incorporation to be approximately 60 min and was unaffected by progestin treatment during the early rapid phase of ER mRNA down-regulation. These data demonstrate that progestins cause rapid down-regulation of the ER mRNA and suggest that during the early rapid phase of this effect, reduced transcription of the ER gene rather than altered ER mRNA half-life mediate this effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗

PubMed1996

An amino-terminal truncated progesterone receptor isoform, PRc, enhances progestin-induced transcriptional activity.

Previously we reported the identification of two unique progesterone receptor (PR) messenger RNA transcripts that encode a smaller PR isoform, termed the C-receptor (PRc). These two PR transcripts encode a protein that is N-terminally truncated, so that it lacks the first zinc finger of the DNA binding domain, but still contains a complete hormone binding region with sequences for dimerization and nuclear localization. We also have demonstrated the existence of a 60-kDa progestin-specific binding protein in progestin target cells using a monoclonal antibody directed to the C-terminus of PRs, suggesting that these two novel transcripts generate a truncated form of PR. In this paper, we address the hypothesis that the C-receptor arises from the initiation of translation of a methionine C-terminal to the methionine start sites that generate the larger 94-kDa A and 116-kDa B human PR isoforms. The studies shown here support the postulate that another downstream in-frame methionine within the PR-coding region can serve as a translation initiation site for the generation of a third PR protein. A partial PR complementary DNA, lacking the translation start sites for B- and A-receptors was translated in vitro. The synthetic protein product bound [3H]progestins and unlabeled progestins. The antiprogestin RU486 also competed for this binding. Transfection of this partial PR complementary DNA into PR-negative HeLa cells resulted in progestin-specific binding activity. Because the third PR isoform lacks the first zinc finger of the DNA binding domain, but contains sequences for dimerization, we reasoned that the C-receptor isoform would be transcriptionally in-active and not bind DNA directly. Surprisingly, however, in the presence of A- and/or B-receptors, we found that C-receptors can modulate the transcriptional activity of A- and/or B-receptors using a reporter gene. These studies emphasize that multiple receptor isoforms may have distinct biological properties, and that the truncated C-receptor may play a role in explaining some of the pleiotropic effects of progestins.

Antineoplastic Agents↗

PubMed2004

Intronic hormone response elements mediate regulation of FKBP5 by progestins and glucocorticoids.

Expression of FKBP51, a large molecular weight immunophilin, is strongly enhanced by glucocorticoids, progestins, and androgens. However, the activity of a 3.4-kb fragment of the FKBP51 gene (FKBP5) promoter was only weakly increased by progestin and we show here that it is unresponsive to glucocorticoids and androgens. The entire FKBP5 was scanned for consensus hormone response elements (HREs) using MatInspector. We found that 2 regions of intron E, which are conserved in rat and mouse FKBP5, contain HRE-like sequences with high match scores. Deoxyribonucleic acid fragments (approximately 1 kb in length) containing these regions were amplified and tested in reporter gene assays for steroid responsiveness. One region of intron E of FKBP5 (pIE2) conferred both glucocorticoid and progestin responsiveness to 2 heterologous reporter genes, whereas the other, less-conserved region of intron E (pIE1) was responsive only to progestins. The inclusion of pIE1 upstream of pIE2 (pIE1IE2) enhanced progestin but not glucocorticoid responsiveness. None of the constructs containing intronic sequences was responsive to androgens. Mutation of the putative HREs within pIE1 and pIE2 eliminated hormone responsiveness. Electrophoretic mobility shift assays demonstrated that progesterone receptors (PR) bound to the HRE in pIE1, whereas both PR and glucocorticoid receptors interacted with the HRE in pIE2. These data suggest that distal intronic elements significantly contribute to transcriptional regulation of FKBP5 by glucocorticoids and progestins.

Androgens↗

PubMed1994

Progestin treatment in the dog. I. Effects on growth hormone, insulin-like growth factor I and glucose homeostasis.

The effects of two synthetic progestins, medroxyprogesterone acetate (MPA) and proligestone (PROL), on the release of growth hormone (GH) and glucose metabolism were studied in two groups of eight ovariohysterectomized dogs. Eight injections of long-acting progestins were administered at 3-week intervals. Recovery was studied in four dogs of each treatment group in the 6 months following cessation of progestin administration. Treatment with both MPA and PROL resulted in similar increases in plasma levels of GH and insulin-like growth factor I (IGF-I). The GH responses to both clonidine and growth hormone-releasing hormone became impaired. In neither treatment group did the elevated plasma GH levels decrease after administration of the synthetic somatostatin analogue SMS 201-995. The size and shape of the pituitary gland were not changed by progestin treatment. After cessation of progestin administration, basal plasma levels of GH and IGF-I did not return to pretreatment values. The GH response to growth hormone-releasing hormone remained impaired for at least 6 months after the last progestin administration. In both treatment groups, glucose homeostasis was sustained initially by increased insulin production. Prolonged treatment with MPA and PROL resulted in glucose intolerance. No amelioration was observed during the recovery period in either group. A small number of dogs developed diabetes mellitus. In more than 50% of the dogs in both treatment groups small mammary tumours developed. The recently discovered local production of GH probably played a role in mammary tumorigenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗

PubMed1989

Oestrogen and progestin receptors as prognostic indicators in endometrial cancer. A review of the literature.

The history of research on oestrogen and progestin receptors in endometrial cancer goes back about 20 years. Summarized data from several clinical studies demonstrate that cytosol oestrogen (ERC) and progestin receptors (PRC) are clinically useful indicators of prognosis. Absence of receptor or its low concentration is indicative of an increased risk of recurrent malignancy. In this respect PRC tends to be more sensitive than ERC. In some studies PRC assay appeared to be more strongly correlated to prognosis than any of the conventional clinico-pathological parameters. In addition, the information obtained by ERC and/or PRC assay is independent of and additional to the classical prognostic indicators. The value of ERC and PRC assay in predicting the sensitivity of endometrial cancer to progestin therapy is of clinical interest. The accumulated data for many clinical trials show that in detecting the non-responders to progestin therapy negative results of ERC and PRC give similar information with an accuracy of about 90%. In identifying responders to progestin therapy, a positive PRC result appeared to give more precise information than a positive ERC, the accuracy being about 75% for PRC. The use of the combination of ERC and PRC determination as a prognostic indicator or predictor of sensitivity to progestin therapy does not significantly increase the information available by PRC measurement alone. Hence, whatever used--a biochemical ligand binding technique or immunohistochemical staining--PRC determination alone seems recommendable for clinical purposes.

Female↗

PubMed1987

Progesterone and progestins modulate beta-endorphin concentrations in the hypothalamus and in the pituitary of castrated female rats.

Hypothalamic and pituitary beta-endorphin (B-EP) concentrations are modified by ovariectomy and estrogen treatments, supporting a direct interaction between this peptidergic system and gonadal steroids. Because the use of progestins is becoming even more diffuse in clinical practice, we evaluated the effect of progesterone and of the synthetic progestins medroxyprogesterone acetate (MPA), norethisterone acetate (NET) and desogestrel on the concentration of B-EP in the medial-basal hypothalamus and the anterior and neurointermediate pituitary lobes in ovariectomized rats (OVX), treated or untreated with estradiol benzoate (EB). B-EP concentrations were significantly increased by desogestrel in the anterior lobe and by progesterone, desogestrel and medroxyprogesterone acetate in the neurointermediate lobe. Progesterone and progestins significantly reduced B-EP increase induced by estradiol benzoate in the anterior lobe. Estradiol benzoate treatment did not modify the effect of progesterone and desogestrel on B-EP in the neuro-intermediate pituitary lobe. Norethisterone acetate and progesterone increased B-EP concentrations in the medial-basal hypothalamus, while the other steroids were inactive. In contrast, in the hypothalamus all progestins attenuated the increase of B-EP induced by estradiol benzoate (p less than 0.01). These data indicate that progesterone and progestins modulate the hypothalamic and pituitary B-EP concentrations in concert with estrogens. The capacity of progestins to modify the hypothalamic contents of B-EP may represent one of the mechanisms of action of these steroids in influencing brain function.

Animals↗

PubMed2000

Using progestins in clinical practice.

Progestational agents have many important functions, including regulation of the menstrual cycle, treatment of dysfunctional uterine bleeding, prevention of endometrial cancer and hyperplastic precursor lesions, and contraception. Because of the reported side effects of synthetic analogs called "progestins," there has been interest in replicating the natural hormone for clinical use. Natural progesterone is obtained primarily from plant sources and is currently available in injectable, intravaginal and oral formulations. An oral micronized progesterone preparation has improved bioavailability and fewer reported side effects compared with synthetic progestins. Adolescents and perimenopausal women may require progestational agents for the treatment of dysfunctional uterine bleeding resulting from anovulatory cycles. These agents may also be used in women at risk for endometrial hyperplasia because of chronic unopposed estrogen stimulation. Progestin-only contraceptives can be used in women with contraindications to estrogen; however, efficacy requires rigorous compliance. New progestins for use in combination oral contraceptive pills were specifically developed to reduce androgenic symptoms. It is unclear whether these progestins increase the risk of venous thromboembolic disease. Progestin-only emergency contraception offers a regimen that is more effective than combination oral contraceptive pills, with fewer reported side effects.

Amenorrhea↗

PubMed2002

Postmenopausal estrogen and progestin use in relation to breast cancer risk.

Epidemiological evidence now consistently supports a modest increase in breast cancer risk among women using postmenopausal hormones, usually estrogens. Less is known regarding how the addition of progestin affects breast cancer risk. The objective of this study was to investigate the type and duration of postmenopausal therapy and breast cancer risk. We performed a multicenter population-based case-control study set in Massachusetts, New Hampshire, and Wisconsin. The subjects were 5298 postmenopausal women (age range, 50-79 years) with a new diagnosis of invasive breast cancer from statewide tumor registries. For comparison, 5571 controls were randomly selected from population lists. Participants completed a structured telephone interview covering hormone use and breast cancer risk factors. Multivariable regression models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). The RR for breast cancer increased with longer durations of hormone use, about 2%/year for estrogen alone (RR, 1.02; 95% CI, 1.01-1.03) and 4%/year for estrogen-progestin use (RR, 1.04; 95% CI, 1.01-1.08). Estrogen-progestin use that was both recent and long term (>5 years in duration) was more strongly associated with breast cancer risk (RR, 1.57; 95% CI, 1.15-2.14) than similar use of estrogen alone (RR, 1.39; 95% CI, 1.17-1.65). In estrogen-progestin users, risks were similar for sequential and continuous use regimens but perhaps stronger for lobular than ductal breast cancer. Use of progestin alone was associated with a doubling of risk (RR, 2.09; 95% CI, 1.07-4.07 for ever use versus nonuse). Estrogen-progestin use, both sequential and continuous, appears to be more strongly associated with risk of breast cancer than use of estrogen alone.

Age Distribution↗