Risks of breast and endometrial cancer after estrogen and estrogen–progestin replacement

Objective: We studied the risk of breast and endometrial cancer in a cohort of 11,231 Swedish women prescribed different replacement hormone regimens.Methods: All 10,472 women at risk of developing breast cancer and 8,438 women at risk of endometrial cancer were followed up from the time of the questionnaire in 1987–88 through 1993, by record-linkages to the National Swedish Cancer Registry. Using data from a questionnaire we analyzed the relationships between hormone exposures and cancer risk, with non-compliers and users of less than 1 year as a reference group.Results: For breast cancer, women reporting use of estrogens combined with progestins had evidence of an increased risk relative to women denying intake or taking hormones for less than 1 year; relative risk (RR) = 1.4 (95% confidence interval 0.9–2.3) after 1–6 years of intake, and RR=1.7 (95% CI 1.1–2.6) after more than 6 years. This excess risk seemed confined to recent exposure. We found no association with intake of estrogens alone using non-compliers and short-term takers as the reference group. The risk of invasive endometrial cancer was increased four-fold in women using medium-potency estrogens alone for 6 years or longer, RR = 4.2 (95% CI 2.5–8.4). Women on such long-term progestin-combined treatment had a lower, non-significant, excess risk (RR = 1.4; 95% CI 0.6–3.3).Conclusions: We conclude that long-term recent use of estrogen–progestin combined replacement therapy may increase the risk of breast cancer. Exposure to estrogen alone substantially elevates the risk of endometrial cancer, an increase that can be reduced or perhaps avoided by adding progestins.     

Celastrol inhibits the growth of estrogen positive human breast cancer cells through modulation of estrogen receptor α

We studied the chemopreventive efficacy of indole-3-carbinol (I3C), a phytochemical found in cruciferous vegetables, to inhibit tobacco carcinogen-induced lung adenocarcinoma in A/J mice when given following post-initiation or progression protocol. Moreover, we assessed the potential mechanisms responsible for the anticancer effects of I3C. Post-initiation administration of I3C decreased the multiplicity of surface tumors as well as all forms of histopathological lesions, including adenocarcinoma, whereas administration of the compound during tumor progression failed to decrease the multiplicity of surface tumors and early forms of microscopic lesions but reduced the frequency of adenocarcinoma. Mechanistic studies in A549 lung adenocarcinoma cells indicated that the lung cancer preventive effects of I3C are mediated, at least in part, via modulation of the receptor tyrosine kinase/PI3K/Akt signaling pathway.     

How does the estrogen receptor work?

In breast cancer, interruption of estrogen receptor (ER)-alpha function is an effective therapeutic strategy. Despite the clinical benefit of interruption of ER-alpha function, the precise biological action of ER-alpha in breast tumors is not completely understood. Results of a recent study show that ER-alpha promotes growth of breast cancer cells by targeting expression of signaling components of the insulin-like growth factor system. Intriguingly, the authors of this study raise the possibility that unliganded ER-alpha itself may affect gene expression and breast cancer biology, and they suggest a potential mechanism for ER-alpha to stimulate proliferation in breast cancer.     

Prenylation inhibitors stimulate both estrogen receptor α transcriptional activity through AF-1 and AF-2 and estrogen receptor β transcriptional activity

A considerable body of research indicates that mammary gland branching morphogenesis is dependent, in part, on the extracellular matrix (ECM), ECM-receptors, such as integrins and other ECM receptors, and ECM-degrading enzymes, including matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). There is some evidence that these ECM cues affect one or more of the following processes: cell survival, polarity, proliferation, differentiation, adhesion, and migration. Both three-dimensional culture models and genetic manipulations of the mouse mammary gland have been used to study the signaling pathways that affect these processes. However, the precise mechanisms of ECM-directed mammary morphogenesis are not well understood. Mammary morphogenesis involves epithelial 'invasion' of adipose tissue, a process akin to invasion by breast cancer cells, although the former is a highly regulated developmental process. How these morphogenic pathways are integrated in the normal gland and how they become dysregulated and subverted in the progression of breast cancer also remain largely unanswered questions.     

Clinical significance of estrogen receptor β in breast cancer

To estimate the clinical significance of estrogen receptor (ER) β in breast cancer we reviewed some reports and compared them with our preliminary results. The structure of ER β is similar to that of ER α. The DNA binding domain of ER β is 96% conserved compared with ER α, and the ligand binding domain shows 58% conserved residues, suggesting that both receptors can bind estrogen responsive elements on target genes and that they may also bind similar ligand. The target tissues of ER β such as testis, prostate, lung, brain, thymus, and ovary, are different from those of ER α, ovary, uterus, endometrium, and breast. Although the function of ER β in breast cancer progression is not well understood, 30-50% of breast cancers may express ER β mRNA signals. Additionally, ER β may be a useful prognostic factor in patients with breast cancer, because tumors that co-expressed ER α and ER β might be node positive and tend to be of higher grade. Further characterization of the function of ER β and its isoforms in breast cancer is warranted.     

Value of post-operative reassessment of estrogen receptor α expression following neoadjuvant chemotherapy with or without gefitinib for estrogen receptor negative breast cancer

The NICE trial was designed to evaluate the possible benefits of adding epidermal growth factor receptor targeted therapy to neoadjuvant chemotherapy in patients with estrogen receptor α (ER) negative and operable breast cancer. Preclinical data have suggested that signalling through the ErbB receptors or downstream effectors may repress ER expression. Here the authors investigated whether gefitinib, given neoadjuvant in combination with epirubicin and cyclophosphamide (EC), could restore ER expression. Eligible patients in the NICE trial were women with unilateral, primary operable, ER negative invasive breast cancer ≥2 cm. Material from patients randomized and completing treatment (four cycles of neoadjuvant EC plus 12 weeks of either gefitinib or placebo) in the NICE trial having available ER status both at baseline and after neoadjuvant treatment were eligible for this study. Tumors with indication of changed ER phenotype (based on collected pathology reports) were immunohistochemically reassessed centrally. 115 patients were eligible for this study; 59 patients in the gefitinib group and 56 patients in the placebo group. Five (4.3%) of 115 tumors changed ER phenotype from negative to positive. A change was seen in three patients in the gefitinib (5.1%) and in two patients in the placebo (3.6%) group with a difference of 1.51% (95% CI, −6.1–9.1). Results of the NICE trial have been reported previously. Post-operative reassessment of ER expression changed the assessment of ER status in a small but significant fraction of patients and should, whenever possible, be performed following neoadjuvant chemotherapy for ER negative breast cancer. Gefitinib did not affect the reversion rate of ER negative tumors.     

Reversal of estrogen‐resistance in murine mammary adenocarcinomas

From mouse mammary progestindependent (PD) adenocarcinomas induced with medroxyprogesterone acetate (MPA) we developed several in vivo lines that are maintained by subcutaneous syngeneic passages in MPAtreated mice and express estrogen (ER) and progesterone receptors (PR). Although most lines remained PD, with time some progestinindependent (PI) variants arose. Both PD and PI tumors regress with estrogen treatment although estrogenresistant variants may also arise. The object of this paper was to investigate the reversibility of estrogenresistance and its possible relation with hormone receptor downregulation. Tumor regression was induced in a progestinindependent tumor line (BET) by treatment with a 5mg 17estradiol (E2) silastic pellet. One of the tumors started to grow disclosing an estrogenresistant pattern of growth. This tumor line (BETR) was transplanted into E2treated and untreated animals (n= 4–6), selecting for the next passage tumors growing in treated animals. Seven new sublines were obtained at different passages by selecting for the next passage the tumors that had grown in untreated mice (BETRaBETRg), until no tumors grew in E2treated mice. ER and PR were measured by a ligandbinding, dextrancoated charcoal method using a single saturating point. From the seven sublines initiated, the first four proved to be reversible after 3–6 generation transplantation and the last three did not revert. A difference in PR expression between BET and BETR (p < 0.05) was registered, but it did not correlate with the specific hormone behavior since two reverted lines had a pattern similar to that of BET and the other two were similar to BETR. The expression of PR was higher in E2treated mice (p < 0.05) and highly variable in the parental line. This led us to study the expression of PR at different stages of the estrous cycle. Higher levels of PR were observed in proestrous, estrous, and metestrous (p < 0.05) than in diestrous, and undetectable levels were found in ovariectomized mice. No differences in ER expression were detected during the estrous cycle. It can be concluded that under certain experimental conditions, estrogenresistance is a reversible phenomenon. The experimental manipulation of hormone resistance may help develop strategies to modify the response to antihormones in humans.     

Unopposed estrogen and estrogen plus progestin menopausal hormone therapy and lung cancer risk in the NIH–AARP Diet and Health Study Cohort

Purpose  

Previous studies have reported that lung cancer risk may be decreased, increased, or unaffected by prior use of menopausal hormone therapy (MHT).     

Linking estrogen receptor β expression with inflammatory bowel disease activity

Crohn disease (CD) and ulcerative colitis (UC) are chronic forms of inflammatory bowel disease (IBD) whose pathogenesis is only poorly understood. Estrogens have a complex role in inflammation and growing evidence suggests that these hormones may impact IBD pathogenesis. Here, we demonstrated a significant reduction (p < 0.05) of estrogen receptor (ER)β expression in peripheral blood T lymphocytes from CD/UC patients with active disease (n = 27) as compared to those in remission (n = 21) and healthy controls (n = 29). Accordingly, in a subgroup of CD/UC patients undergoing to anti-TNF-α therapy and responsive to treatment, ERβ expression was higher (p < 0.01) than that observed in not responsive patients and comparable to that of control subjects. Notably, ERβ expression was markedly decreased in colonic mucosa of CD/UC patients with active disease, reflecting the alterations observed in peripheral blood T cells. ERβ expression inversely correlated with interleukin (IL)-6 serum levels and exogenous exposure of both T lymphocytes and intestinal epithelial cells to this cytokine resulted in ERβ downregulation. These results demonstrate that the ER profile is altered in active IBD patients at both mucosal and systemic levels, at least in part due to IL-6 dysregulation, and highlight the potential exploitation of T cell-associated ERβ as a biomarker of endoscopic disease activity.     

Estrogen metabolism in menopausal hormone users in the women's health initiative observational study: Does it differ between estrogen plus progestin and estrogen alone?

The WHI found an unexpected reduced breast cancer risk in women using CEE alone. We hypothesized CEE alone induces estrogen hydroxylation along the 2-pathway rather than the competing 16-pathway, a pattern linked to reduced postmenopausal breast cancer risk. One thousand eight hundred and sixty-four women in a WHIOS case–control study of estrogen metabolism and ovarian and endometrial cancer were studied of whom 609 were current E + P users (351 used CEE + MPA), while 272 used E alone (162 used CEE). Fifteen EM were measured, and analyses were conducted for each metabolite, hydroxylation pathway (2-, 4-, or 16-pathway) and ratios of pathway concentrations using inverse probability weighted linear regression. Compared to E + P users, all EM were higher in E alone users (significant for unconjugated estrone, total/conjugated estradiol, total/unconjugated 2-methoxyestrone, 4-methoxyestrone and unconjugated estriol). The relative concentrations of 2- and 4-pathway EM did not differ between the MHT users (2-pathway EM comprised 15% and 4-pathway EM <2% of the total), but 16-pathway EM were lower in E alone users (p = 0.036). Ratios of 2- and 4-pathway EM compared to 16-pathway EM were significantly higher in E alone compared to E + P users. Similar but not significant patterns were observed in CEE-alone and CEE + MPA users. Our data suggest that compared to E + P users, women using E alone have more extensive metabolism via the 2- vs. the competing 16-pathway. This is consistent with epidemiologic evidence of reduced postmenopausal breast cancer risk associated with this metabolic profile and may provide a clue to the breast cancer risk reduction in CEE alone users during the WHI.     

Action of “pure” antiestrogens in inhibiting estrogen receptor action

Summary The mechanism of action of the pure antiestrogens ICI 164384 and ICI 182780 has been investigated. Both antagonists are steroidal antiestrogens with 7-alkylamide side-chains. The antiestrogens reduce the cellular content of the estrogen receptor by reducing the half-life of the protein. A potential mechanism for this effect is suggested by the observation that the DNA binding activity of receptors which have been over-expressed in cells was inhibitedin vitro. The inhibitory activity of analogues of ICI 164384 with different side chain lengths correlates with their ability to function as pure antiestrogensin vivo. Since the estrogen binding site overlaps with residues involved in dimerisation, the antiestrogens are likely to bind to a similar site and may therefore interfere with receptor dimerisation in the hormone binding domain by means of the 7 side-chain. We propose that the increased turnover of the receptor in the presence of ICI 164384 and ICI 182380 is a consequence of impaired dimerisation of the proteins.     

Stromal estrogen receptor-α promotes tumor growth by normalizing an increased angiogenesis

Estrogens directly promote the growth of breast cancers that express the estrogen receptor α (ERα). However, the contribution of stromal expression of ERα in the tumor microenvironment to the protumoral effects of estrogen has never been explored. In this study, we evaluated the molecular and cellular mechanisms by which 17β-estradiol (E2) impacts the microenvironment and modulates tumor development of ERα-negative tumors. Using different mouse models of ER-negative cancer cells grafted subcutaneously into syngeneic ovariectomized immunocompetent mice, we found that E2 potentiates tumor growth, increases intratumoral vessel density, and modifies tumor vasculature into a more regularly organized structure, thereby improving vessel stabilization to prevent tumor hypoxia and necrosis. These E2-induced effects were completely abrogated in ERα-deficient mice, showing a critical role of host ERα. Notably, E2 did not accelerate tumor growth when ERα was deficient in Tie2-positive cells, even in mice grafted with wild-type bone marrow. These results were extended by clinical evidence of ERα-positive stromal cell labeling in the microenvironment of human breast cancers. Together, our findings therefore show that E2 promotes the growth of ERα-negative cancer cells through the activation of stromal ERα (extra-hematopoietic Tie-2 positive cells), which normalizes tumor angiogenesis and allows an adaptation of blood supply to tumors, thereby preventing hypoxia and necrosis. These findings significantly deepen mechanistic insights into the impact of E2 on tumor development with potential consequences for cancer treatment.     

Is BRCA1/BRCA2-related breast carcinogenesis estrogen dependent?

Estrogen is a well known promoting factor of sporadic breast carcinoma. With regard to hereditary breast carcinoma, such as in BRCA1/BRCA2 syndromes, to date, the effects of estrogens on risk modification are not clear. Several studies have shown that prophylactic oophorectomy may decrease the risk of breast carcinoma in BRCA1/BRCA2 mutation carriers. Moreover, adjuvant tamoxifen therapy for primary breast carcinoma appears to diminish the risk of a second breast malignancy in BRCA1 mutation carriers. Conversely, exogenous estrogens, such as oral contraceptives, may increase the risk of breast carcinoma in familial breast cancer, as suggested by clinical studies. Paradoxically, the majority of BRCA1-related breast carcinomas are negative for ER. There is some biologic evidence of interactions between estrogens and BRCA proteins. BRCA1 expression could be induced by estradiol in experimental models, whereas recent studies indicate that BRCA1 modifies the regulatory effects of the estrogen receptor (ER) alpha (ERalpha). Prospective studies will be required to estimate the potential benefits of estrogen suppression therapies for the prevention and adjuvant treatment of BRCA1/BRCA2-related breast carcinomas.     

Withaferin a suppresses estrogen receptor-α expression in human breast cancer cells

We have shown previously that withaferin A (WA), a promising anticancer constituent of Ayurvedic medicine plant Withania somnifera, inhibits growth of MCF-7 and MDA-MB-231 human breast cancer cells in culture and MDA-MB-231 xenografts in vivo by causing apoptosis. However, the mechanism of WA-induced apoptosis is not fully understood. The present study was designed to systematically determine the role of tumor suppressor p53 and estrogen receptor-α (ER-α) in proapoptotic response to WA using MCF-7, T47D, and ER-α overexpressing MDA-MB-231 cells as a model. WA treatment resulted in induction as well as increased S15 phosphorylation of p53 in MCF-7 cells, but RNA interference of this tumor suppressor conferred modest protection at best against WA-induced apoptosis. WA-mediated growth inhibition and apoptosis induction in MCF-7 cells were significantly attenuated in the presence of 17β-estradiol (E2). Exposure of MCF-7 cells to WA resulted in a marked decrease in protein levels of ER-α (but not ER-β) and ER-α regulated gene product pS2, and this effect was markedly attenuated in the presence of E2. WA-mediated down-regulation of ER-α protein expression correlated with a decrease in its nuclear level, suppression of its mRNA level, and inhibition of E2-dependent activation of ERE2e1b-luciferase reporter gene. Ectopic expression of ER-α in the MDA-MB-231 cell line conferred partial but statistically significant protection against WA-mediated apoptosis, but not G2/M phase cell cycle arrest. Collectively, these results indicate that WA functions as an anti-estrogen, and the proapoptotic effect of this promising natural product is partially attenuated by p53 knockdown and E2-ER-α.