Genetic susceptibility and environmental estrogen-like compounds

Environmental chemicals with estrogenic activities have been suggested to be able to interact with the endocrine system. Endogenous estrogen is synthesized in the ovarian theca cells of premenopausal women or in the stromal adipose cells of the breast of postmenopausal women and minor quantities in peripheral tissue. These cells, as well as breast tissue, express all the necessary enzymes for this synthesis, CYP17, CYP11a, CYP19, 17-beta-hydroxysteroid hydrogenase, steroid sulfatase as well as enzymes further hydroxylating estradiol, such as CYP1A1, CYP3A4, CYP1B1, catechol-o-methyltransferase (COMT). Polymorphisms in these enzymes may have a possible role in the link between environmental estrogens and hormone-like substances and the interindividual risk of breast cancer.     

Soy isoflavones, CYP1A1, CYP1B1, and COMT polymorphisms, and breast cancer: a case-control study in southwestern China

CYP1A1, CYP1B1, and COMT are key enzymes involved in estrogen metabolism. Soy isoflavones, phytoestrogens found in soy foods, may modify the activity of these enzymes. A case-control study was conducted to assess the associations between soy isoflavone intake and the CYP1A1 Ile462Val, CYP1B1 Val432Leu, and COMT Val158Met polymorphisms and breast cancer, as well as their combined effects on breast cancer. A total of 400 newly diagnosed breast cancer cases and 400 healthy controls were recruited. Participants' daily intake of soy isoflavones (DISI [mg/day]) was calculated and transformed to energy-adjusted DISI by the residual method. Gene sequencing was used to analyze CYP1A1, CYP1B1, and COMT polymorphisms. Adjusted odds ratios (aORs) and 95% confidence intervals (95% CIs) were estimated by conditional logistic regression. A strong protective dose-dependent effect of energy-adjusted DISI on breast cancer was found in both pre- and postmenopausal women (P(trend)??1, OR 95% CIs exclude 1). In premenopausal women, only carrying CYP1B1 Leu/Leu was associated with breast cancer risk (aOR?=?2.05, 95% CI: 1.11-3.79). Carrying CYP1A1 Val/Val was related to breast cancer risk only among all women. A stratified analysis was performed at two levels of energy-adjusted DISI, with wildtype homozygous genotypes and low energy-adjusted DISI as the reference. In the high energy-adjusted DISI subgroup, carrying the CYP1B1 Leu/Leu genotype did not affect breast cancer risk in either all women or in the menopausal subgroups, compared with the reference. Overall, in Han Chinese women, carrying CYP1A1 Val/Val and COMT Met/Met appears to be associated with breast cancer risk, especially in postmenopausal women. CYP1B1 susceptible genotypes (Val/Leu or Leu/Leu) also contribute to increased breast cancer risk, regardless of menopausal status, but high soy isoflavone intake may reduce this risk.     

Expression of sex steroid receptors and IGF-1 mRNA in breast tissue--effects of hormonal treatment

The mechanisms behind increased breast tissue proliferation and a possibly increased breast cancer risk in women using hormonal contraception (HC) and hormonal replacement therapy (HRT) are incompletely understood. We analyzed breast tissue from 20 premenopausal and seven postmenopausal women undergoing reduction mammoplasties for estrogen receptor (ER) and progesterone receptor (PR) content as well as mRNA levels for ER, PR and insulin-like growth factor-1 (IGF-1). The receptor values were correlated to IGF-1 mRNA concentrations and levels of steroid and peptide hormones and SHBG. In women using HC, we found significantly lower ER values (p=0.02) but non-significantly lower ER mRNA levels compared to those in naturally cycling women. PR and PR mRNA were no different. Women on HC displayed a higher breast tissue proliferation (p=0.05) expressed as Ki-67, MIB-1 positivity, which was correlated with IGF-1 mRNA (r_s=0.82, p=0.04). Since the concentration of sex steroid receptors in breast tissue is comparatively low and steroid receptors are down-regulated during hormonal treatment, mechanisms other than direct sex steroid receptor action are likely to be present. Our results suggest a role for IGF-1 in the proliferative response of breast tissue during exogenous hormonal treatment.     

The oestrogen paradox: a hypothesis

Epidemiological and observational studies suggest that oestrogens, when used as hormonal therapy in post-menopausal women, can increase the risk of breast cancer if used long term. However, more recent data suggest that short-term use in sub-groups of post-menopausal women significantly decreases the risk of breast cancer. This beneficial effect is also observed when high-dose oestrogen is administered to post-menopausal women with breast cancer to cause tumour regression, a phenomenon which commonly occurs. We consider these divergent responses to oestrogen to represent a "paradox". Data from our own and other investigative groups suggest a hypothesis to explain this paradox. Deprivation of oestradiol in model systems causes cells to adapt and to undergo apoptosis in response to oestrogen. This occurs through the Fas/Fas ligand death receptor pathway and through alterations in apoptotic mechanisms mediated by mitochondria. This process of programmed cell death may explain the regression of established breast cancer with oestrogen administration and the diminution in the rate of new breast cancer diagnoses recently reported. Our hypothesis is based upon pathological data indicating the presence of a "reservoir" of undiagnosed breast cancer in the population of women who would be starting on oestrogens as menopausal hormonal therapy. The long-term increased risk of breast cancer may then reflect different mechanisms. Oestrogens can cause mutations through enhancement of the rate of cell division and concomitantly the error rate in DNA replication. In addition, oestrogens can be metabolised to directly genotoxic compounds. These carcinogenic processes take much longer, since a number of mutations must accumulate before resulting in breast cancer. These hypotheses regarding oestrogen-induced apoptosis in the short term and carcinogenesis in the long term now require rigorous verification but would serve to explain the "oestrogen paradox".     

Nutrients and nipple aspirate fluid composition: the breast microenvironment regulates protein expression and cancer aetiology

The aetiology of breast cancer is complex and multifactorial, and may include diet and xenobiotic compounds. A change in diet affects nutrient levels in blood, but to what extent diet can affect micronutrient concentrations in the breast is not yet well established. Breast nipple aspirate fluids (NAF) can be non-invasively obtained from the breast in most women; it represents a biological tool to assess metabolic changes in the breast ductal microenvironment. A wide variation in biomolecular and hormonal composition of NAFs collected from healthy and breast cancer patient may be due to genetic and nutritional factors; however, micro- and macro-nutrients may influence the secretory status of these women, thus NAF composition and risk of breast carcinoma. The aim of this overview is to highlight the detrimental/beneficial role that diet-related compounds in nipple aspirate fluid can have in breast cancer risk.     

Endogenous oestrogens and breast cancer risk in premenopausal and postmenopausal women

Breast cancer risk is strongly related to several reproductive and hormonal factors, but the nature of the effects of endogenous oestrogens has been difficult to establish. Data are now available from several large prospective studies with biobanks of stored serum, enabling better characterization of the associations of endogenous oestrogens, and other endogenous hormones, with breast cancer risk. In postmenopausal women, relatively high serum concentrations of oestradiol are associated with a more than twofold increase in the risk for breast cancer, and this probably explains the increase in risk in obese postmenopausal women. In premenopausal women the data available on oestrogens are more limited and difficult to interpret due to the large variations in endogenous oestrogens during the menstrual cycle, but are compatible with a positive association between oestradiol and breast cancer risk. There is also evidence that breast cancer risk is positively associated with androgens, prolactin and insulin-like growth factor-I. Further data are required, with better assays and repeat measures, to provide more accurate estimates of risk and to clarify the role of oestrogens in premenopausal women and the roles of other endogenous hormones.     

Phenol red in the culture medium strongly affects the susceptibility of human MCF-7 cells to roscovitine

Estrogens play an important role in the growth and terminal differentiation of the mammary gland. Prolonged exposure to estrogens seems to predispose women to breast cancer. It recently became evident that not only the intrinsic hormonal status but also external factors such as the occurrence of pharmaceuticals and chemicals with hormone activity in the environment may put women at greater risk of developing breast cancer. We focused on the interference of endocrine disruptors in breast cancer therapy. We observed that phenol red added to the culture medium strongly promoted the cell proliferation and cell cycle progression of human cells expressing the estrogen receptor, and affected their susceptibility to chemotherapy.     

Phytoestrogens as natural prodrugs in cancer prevention: a novel concept

It has been generally accepted that regular consumption of fresh fruits and vegetables is linked with a relatively low incidence of cancers (e.g. breast, cervix, and colon). A number of plant-derived compounds have been identified that are considered to play a role in cancer prevention. However, at present there is no satisfactory explanation for the cancer preventative properties of the above-mentioned compound groups. The current review is an effort to develop a consistent and unambiguous model that explains how some plant-derived compounds can prevent tumour development. The model is based on recent discoveries in the fields of genomics and drug-metabolism; notably, the discovery that CYP1 genes are highly expressed in developing tumour cells but not in the surrounding tissue, and that a variety of plant-derived compounds are substrates for the CYP1 enzymes. Our hypothesis is that some dietary compounds act as prodrugs, i.e. compounds with little or no biological effect as such, but become pharmaceutically effective when activated. More specifically, we state that the abovementioned prodrugs are only activated in CYP1-expressing cells—i.e. cells in the early stages of tumour development—to be converted into compounds which inhibit cell growth. Thus, the prodrugs selectively kill precancerous cells early in tumour development. The review focuses on the identification of naturally-occurring prodrugs that are activated by the tumour-specific CYP1 enzymes and aims to assess their role in cancer prevention.     

On the significance of in situ production of oestrogens in human breast cancer tissue

We have previously shown that human breast cancer is autonomous in the regulation of its intra-tissue oestradiol concentration. Breast fatty tissue does not have this capacity, but rather reflects changes in the peripheral oestradiol concentration. To further evaluate the relative contribution of breast cancer and fatty tissue to the maintenance of tumour oestradiol we investigated whether a tumour-directed gradient in aromatase activity and oestrogen levels existed in mastectomy specimens. No such gradient was found, however, for aromatase, oestrone, oestradiol and their sulphates. Aromatase activity (expressed per gram of tissue) and the concentrations of oestradiol, oestradiol sulphate and oestrone sulphate were higher in tumour than in breast fatty tissue. Fatty tissue had a higher oestrone concentration. It is tentatively concluded that breast tumour aromatase activity is more important for the maintenance of tumour oestradiol levels than aromatase in breast fatty tissue.     

On the significance of in situ production of oestrogens in human breast cancer tissue.

We have previously shown that human breast cancer is autonomous in the regulation of its intra-tissue oestradiol concentration. Breast fatty tissue does not have this capacity, but rather reflects changes in the peripheral oestradiol concentration. To further evaluate the relative contribution of breast cancer and fatty tissue to the maintenance of tumour oestradiol we investigated whether a tumour-directed gradient in aromatase activity and oestrogen levels existed in mastectomy specimens. No such gradient was found, however, for aromatase, oestrone, oestradiol and their sulphates. Aromatase activity (expressed per gram of tissue) and the concentrations of oestradiol, oestradiol sulphate and oestrone sulphate were higher in tumour than in breast fatty tissue. Fatty tissue had a higher oestrone concentration. It is tentatively concluded that breast tumour aromatase activity is more important for the maintenance of tumour oestradiol levels than aromatase in breast fatty tissue.     

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.     

Role of xenobiotic metabolizing gene polymorphisms in breast cancer susceptibility and treatment outcome

Metabolic activation and inactivation of potential genotoxic agents occur by Phase I and Phase II enzymes in multiple interactions. An expanding body of literature demonstrates that ethnic differences in breast cancer incidence may be partly caused by host genetic factors particularly genetic polymorphisms of these carcinogen-metabolizing enzymes. The present case-control study aimed at identification of such low penetrance breast cancer susceptibility genes in 224 Indian women and to investigate the potential effects of their polymorphisms on sporadic breast cancer risk. The main objective of the study was to evaluate the effects of genetic polymorphisms of the xenobiotic metabolizing genes CYP1A1, GSTM1 and GSTT1 on breast cancer risk by PCR-RFLP and DNA sequencing. Our results showed a significant association between CYP1A1 m1, m2 polymorphisms and breast cancer risk; however there was a lack of association between GSTM1 null deletion and breast cancer. The associations of CYP1A1, GSTM1 and GSTT1 genotypes with breast cancer risk were more pronounced among the pre-menopausal patients. Combined genotype analysis revealed the CYP1A1 m2 ValVal-GSTM1 homozygous null deletion genotype combinations to be associated with the highest risk of breast cancer (OR=10.3, 95% CI=1.2-86.1). Correlations with clinicopathological factors and treatment outcome were also analyzed for predicting disease free survival by univariate and multivariate analysis. Significant differences in disease free survival between the wild and polymorphic genotypes were observed only for CYP1A1 m2, GSTT1 genotypes. Our results based on the analysis of functionally relevant polymorphisms in these low penetrance genes may provide a better model that would exhibit additive effects on individual susceptibility to breast cancer. Such genotype analysis resulting in a high-risk profile holds considerable promise for individualizing screening and therapeutic intervention in breast cancer. Hence, the present study may provide strong supportive evidence for genetic interactions in the etiology of breast cancer.     

Environmental contaminants in pathogenesis of breast cancer

This review is an attempt to comprehend the diverse groups of environmental chemical contaminants with a potential for pathogenesis of breast cancer, their probable sources and the possible mechanisms by which these environmental contaminants act and interplay with other risk factors. Estrogens are closely related to the pathogenesis of breast cancer. Oxidative catabolism of estrogen, mediated by various cytochrome P450 enzymes, generates reactive free radicals that can cause oxidative damage. The same enzymes of estrogenic metabolic pathways catalyze biological activation of several environmental (xenobiotic) chemicals. Xenobiotic chemicals may exert their pathological effects through generation of reactive free radicals. Breast tissue can be a target of several xenobiotic agents. DNA-reactive metabolites of different xenobiotic compounds have been detected in breast tissue. Many phase I and II xenobiotic metabolizing enzymes are expressed in both normal and cancerous breast tissues. These enzymes play a significant role in the activation/detoxification of xenobiotic and endogenous compounds including estrogens. More than 30 carcinogenic chemicals are present in tobacco smoke; many of them are fat-soluble, resistant to metabolism and can be stored in breast adipose tissue. Similarly, pesticides are also known to cause oxidative stress; while some act as endocrine disruptor, some are shown to suppress apoptosis in estrogen sensitive cell lines. Reports have shown an association of smoking (both active and passive) and pesticides with breast cancer risk. However, the issues have remained controversial. Different mutagenic substances that are generated in the cooking process e.g., heterocyclic amines and polycyclic aromatic hydrocarbons (PAHs) can be a threat to breast tissue. PAHs and dioxins exert their adverse effects through the aryl hydrocarbon receptor (AhR), which activates several genes involved in the metabolisms of xenobiotic compounds and endogenous estrogens. These chemicals also induce AhR-dependent mitochondrial dysfunction. Many of the environmental pollutants suppress the immune system, which are implicated to risk. A better understanding about the biological effects of different environmental carcinogenic compounds and determination of their impact on rising incidence of breast cancer will be beneficial in improving preventive policy against breast cancer.     

Oestrogen regulates oestrogen receptor mRNA levels in an oestrogen-responsive human breast cancer cell line

The EFM-19 human breast cancer cell line contains high levels of oestrogen receptor mRNA and is oestrogen responsive for growth. The oestrogen receptor gene appears to be specifically regulated by oestrogens in EFM-19 cells. The induction by oestradiol is half-maximal in the presence of 3 x 10(-11) M oestradiol. LY117018 is a potent antioestrogen with a similar affinity to oestradiol for the oestrogen receptor. LY117018 completely blocks the induction of the oestrogen receptor mRNA by oestradiol when it is present in a 50-fold molar excess. The ability of oestrogens to control the levels of their own receptor in human breast cancer cells has implications for the understanding of oestrogen responsiveness and the amelioration of endocrine therapy.     

Prolactin and endocrine therapy resistance in breast cancer: The next potential hope for breast cancer treatment

Breast cancer, a hormone-dependent tumour, generally includes four molecular subtypes (luminal A, luminal B, HER2 enriched and triple-negative) based on oestrogen receptor, progesterone receptor and human epidermal growth factor receptor-2. Multiple hormones in the body regulate the development of breast cancer. Endocrine therapy is one of the primary treatments for hormone-receptor-positive breast cancer, but endocrine resistance is the primary clinical cause of treatment failure. Prolactin (PRL) is a protein hormone secreted by the pituitary gland, mainly promoting mammary gland growth, stimulating and maintaining lactation. Previous studies suggest that high PRL levels can increase the risk of invasive breast cancer in women. The expression levels of PRL and PRLR in breast cancer cells and breast cancer tissues are elevated in most ER⁺ and ER⁻ tumours. PRL activates downstream signalling pathways and affects endocrine therapy resistance by combining with prolactin receptor (PRLR). In this review, we illustrated and summarized the correlations between endocrine therapy resistance in breast cancer and PRL, as well as the pathophysiological mechanisms and clinical practices. The study on PRL and its receptor would help explore reversing endocrine therapy-resistance for breast cancer.     

Endocrine approaches for the treatment of early and advanced breast cancer in postmenopausal women

Preventing clinical progression is the major treatment goal for both early and advanced breast cancer. For hormone-responsive cases (about 70% of the total), this can necessitate the use of sequential hormone therapies at various points during the patient's life. Newer hormonal therapies, such as the third-generation aromatase inhibitor anastrozole, are now competing with tamoxifen as first choice endocrine therapy in breast cancer. In addition, a further non-steroidal aromatase inhibitor letrozole has been shown to be beneficial when given at completion of 5 years adjuvant tamoxifen. In light of these new data, current treatment paradigms need to be reviewed. Already well established as second-line treatments for advanced breast cancer, the improved risk:benefit profiles of anastrozole and letrozole compared with tamoxifen mean that these agents are now also recognised alternative treatments in the first-line relapse setting. More recent studies demonstrate that anastrozole may also have an improved risk:benefit profile compared with tamoxifen when used as initial adjuvant therapy in early breast cancer. Anastrozole is also being evaluated as a preventative treatment in women at high risk of developing breast cancer. A new addition to the endocrine treatment armamentarium is the oestrogen receptor antagonist fulvestrant, which, unlike tamoxifen, has no agonist effects. Fulvestrant is at least as effective as anastrozole in the second-line treatment of advanced breast cancer, and provides similar benefits to tamoxifen when used as first-line therapy in patients with advanced, hormone receptor-positive tumours.     

Understanding breast cancer risk ‐ where do we stand in 2005?

Breast cancer is the most frequent cancer in women and represents the second leading cause of cancer death among women (after lung cancer). The etiology of breast cancer is still poorly understood with known breast cancer risk factors explaining only a small proportion of cases. Risk factors that modulate the development of breast cancer discussed in this review include: age, geographic location (country of origin) and socioeconomic status, reproductive events, exogenous hormones, lifestyle risk factors (alcohol, diet, obesity and physical activity), familial history of breast cancer, mammographic density, history of benign breast disease, ionizing radiation, bone density, height, IGF- 1 and prolactin levels, chemopreventive agents. Additionally, we summarized breast cancer risk associated with the following genetic factors: breast cancer susceptibility high-penetrance genes (BRCA1, BRCA2, p53, PTEN, ATM, NBS1 or LKB1) and low-penetrance genes such as cytochrome P450 genes (CYP1A1, CYP2D6, CYP19), glutathione S-transferase family (GSTM1, GSTP1), alcohol and one-carbon metabolism genes (ADH1C and MTHFR), DNA repair genes (XRCC1, XRCC3, ERCC4/XPF) and genes encoding cell signaling molecules (PR, ER, TNFalpha or HSP70). All these factors contribute to a better understanding of breast cancer risk. Nonetheless, in order to evaluate more accurately the overall risk of breast tumorigenesis, novel genetic and phenotypic traits need to be identified.     

Ontogeny of the Major Xenobiotic‐Metabolizing Enzymes Expression and the Dietary Lipids Modulatory Effect in the Rat Dimethylbenz(a)anthracene‐Induced Breast Cancer Model

Breast cancer is the most common malignancy in women worldwide. Environmental factors such as xenobiotic exposure and lifestyle and nutrition play a key role in its etiology. This study was designed to evaluate the age‐related changes in the expression of major xenobiotic‐metabolizing enzymes (XMEs) in the rat liver and the mammary gland in the dimethylbenz(a)anthracene‐induced breast cancer model. The influence of dietary lipids on the ontogeny of XMEs was also evaluated. mRNA and protein levels of phase I (CYP1A1, CYP1A2, and CYP1B1) and phase II (NAD(P)H:quinone acceptor oxidoreductase 1 and GSTP1) enzymes were analyzed, as well as their regulation by AhR and Nrf2, respectively. Results showed differences in the phase I enzymes expression, whereas little changes were obtained in phase II. High corn oil and olive oil diets differentially influenced the expression of age‐related changes, suggesting that the different susceptibility to xenobiotic exposure depending upon the age may be modulated by dietary factors.     

Intratumour amount of sex steroids in elderly breast cancer patients. An approach to the biological characterization of mammary tumours in the elderly

Interest in breast cancer in elderly women is growing as a result of the high frequency of cancer in older age groups. We measured tumour concentrations and circulating levels of testosterone, dihydrotestosterone (DHT) and oestradiol in 50 postmenopausal patients: 26 younger than 70 yr (median, 61.5, range 50–69) and 24 older than 70 yr (median, 74.5, range 70–82). Hormones were measured by radioimmunoassay (RIA) after extraction and separation on celite column chromatography. Intratumour levels of the three steroids were lower in the older than in the younger patients, but the difference was statistically significant only for DHT (P = 0.0126). The decrease in the tumour concentrations of testosterone and DHT in the older group was associated with a slight increase in circulating levels, yielding as final result a statistically significant decrease of the tissue/plasma (T/P) ratio of these hormones. No significant difference was observed between groups for oestradiol levels. The blood levels of testosterone, DHT and oestradiol were significantly correlated in the older group, but not in the younger group. In contrast, the tumour amounts of testosterone and DHT were found to be significantly associated only in the < 70 yr group. We concluded that the hormonal environment in which breast cancer develops is different in younger and older postmenopausal patients, and that the difference mainly concerns the intratumour amounts of androgens, suggesting that the steroids concur in the growth regulation of mammary tumours.