Metabolism of estrogens in breast cancer.

This extensive literature compilation reviews major studies on estrogen metabolism in cancer, studies which have led to proposed possible etiological roles of estrogens in human breast cancer. Urinary and plasma estrogen excretion patterns and profiles in women with breast cancer are the topics of part 1. Studies of estrogen profiles in women who are at high-risk for breast cancer are critiqued. The estriol hypothesis is presented and criticised in a chapter. The effects of endocrine ablation on urinary estrogen profiles in breast cancer patients are compiled. Production and metabolism of estrogens in women with breast cancer are rendered, including in vivo biotransformation rates and in vitro transformation data. And the search for estrogen metabolites in women with breast cancer is reviewed. In conclusion it is obvious that the question of whether breast cancer patients have an abnormal metabolism of estrogen has not been answered, but further investigations of estrogen metabolism in breast cancer should be continued because: 1) the possibility that estrogens are carcinogenic has not been ruled out; 2) receptors have been discovered which do correlate with hormone dependency of tumors; 3) present evidence suggests that neoplasm may induce abnormal estrogen metabolism; 4) directional changes of estrogen metabolism that occur in pregnancy may also occur in women with target tissue neoplasia; 5) hepatic tissue's relationship to breast cancer has not received attention; and 6) the role of peripheral aromatization in the pathogenesis of mammary cancer is not yet understood.     

Breast cancer tissue estrogens and their manipulation with aromatase inhibitors and inactivators

Despite the dramatic fall in plasma estrogen levels at menopause, only minor differences in breast tissue estrogen levels have been reported comparing pre- and postmenopausal women. Thus, postmenopausal breast tissue has the ability to maintain concentrations of estrone (E₁) and estradiol (E₂) that are 2–10- and 10–20-fold higher than the corresponding plasma estrogen levels. This finding may be explained by uptake of estrogens from the circulation and/or local estrogen production. Local aromatase activity in breast tissue seems to be of crucial importance for the local estrogen production in some patients while uptake from the circulation may be more important in other patients. Beside aromatase, breast tissue expresses estrogen sulfotransferase and sulfatase as well as dehydrogenase activity, allowing estrogen storage and release in the cells as well as conversions between estrone and estradiol. The activity of the enzyme network in breast cancer tissue is modified by a variety of factors like growth factors and cytokines. Aromatase inhibitors have been used for more than two decades in the treatment of postmenopausal metastatic breast cancer and are currently investigated in the adjuvant treatment and even prevention of breast cancer. Novel aromatase inhibitors and inactivators have been shown to suppress plasma estrogen levels effectively in postmenopausal breast cancer patients. However, knowledge about the influence of these drugs on estrogen levels in breast cancer tissue is limited. Using a novel HPLC-RIA method developed for the determination of breast tissue estrogen concentrations, we measured tissue E₁, E₂ and estrone sulfate (E₁S) levels in postmenopausal breast cancer patients before and during treatment with anastrozole. Our findings revealed high breast tumor tissue estrogen concentrations that were effectively decreased by anastrozole. While E₁S was the dominating estrogen fraction in the plasma, estradiol was the estrogen fraction with the highest concentration in tumor tissue. Moreover, plasma estrogen levels did not correlate with tissue estrogen concentrations. The overall experience with aromatase inhibitors and inactivators concerning their influences on breast tissue estrogen concentrations is summarized.     

Acquired resistance to selective estrogen receptor modulators (SERMs) in clinical practice (tamoxifen & raloxifene) by selection pressure in breast cancer cell populations

Tamoxifen, a pioneering selective estrogen receptor modulator (SERM), has long been a therapeutic choice for all stages of estrogen receptor (ER)-positive breast cancer. The clinical application of long-term adjuvant antihormone therapy for the breast cancer has significantly improved breast cancer survival. However, acquired resistance to SERM remains a significant challenge in breast cancer treatment. The evolution of acquired resistance to SERMs treatment was primarily discovered using MCF-7 tumors transplanted in athymic mice to mimic years of adjuvant treatment in patients. Acquired resistance to tamoxifen is unique because the growth of resistant tumors is dependent on SERMs. It appears that acquired resistance to SERM is initially able to utilize either E₂ or a SERM as the growth stimulus in the SERM-resistant breast tumors. Mechanistic studies reveal that SERMs continuously suppress nuclear ER-target genes even during resistance, whereas they function as agonists to activate multiple membrane-associated molecules to promote cell growth. Laboratory observations in vivo further show that three phases of acquired SERM-resistance exists, depending on the length of SERMs exposure. Tumors with Phase I resistance are stimulated by both SERMs and estrogen. Tumors with Phase II resistance are stimulated by SERMs, but are inhibited by estrogen due to apoptosis. The laboratory models suggest a new treatment strategy, in which limited-duration, low-dose estrogen can be used to purge Phase II-resistant breast cancer cells. This discovery provides an invaluable insight into the evolution of drug resistance to SERMs, and this knowledge is now being used to justify clinical trials of estrogen therapy following long-term antihormone therapy. All of these results suggest that cell populations that have acquired resistance are in constant evolution depending upon selection pressure. The limited availability of growth stimuli in any new environment enhances population plasticity in the trial and error search for survival.     

Estrogen receptor beta in the breast: role in estrogen responsiveness and development of breast cancer

Breast cancer is one of the most common forms of cancer observed in women. Endogenous estrogen is thought to play a major role in its development and estrogen receptor blockers are the most important drugs in its treatment. It has long been thought that any conditions or exposures, which enhance estrogenic responses, would result in an increased risk for breast cancer. The discovery of the second estrogen receptor, ERbeta, which can have effects opposite to those of the well-known 'original' estrogen receptor (now called ERalpha) challenges this simplistic view. In order to understand breast cancer one must first understand how the normal breast is maintained. The functions of ERbeta in the breast remain to be defined but from what we have learnt about its activities in in vitro systems, this estrogen receptor may have a protective role in the breast. Studies in human and rodent breasts as well as in human breast cancer biopsies reveal that ERbeta is by far the more abundant of the two ERs. Despite the role of estrogen in proliferation of the breast, neither of the two ERs appears to located in epithelial cells which divide in response to estrogen. In order to define the functions of ERbeta in the normal and malignant breast, we have created mice in which the ERbeta gene has been inactivated. Studies of the breasts of ERbeta knock out mice (BERKO) revealed abnormal epithelial growth, overexpression of Ki67 and severe cystic breast disease as mice age.     

Estrogen receptor β in the breast: role in estrogen responsiveness and development of breast cancer

Breast cancer is one of the most common forms of cancer observed in women. Endogenous estrogen is thought to play a major role in its development and estrogen receptor blockers are the most important drugs in its treatment. It has long been thought that any conditions or exposures, which enhance estrogenic responses, would result in an increased risk for breast cancer. The discovery of the second estrogen receptor, ERβ, which can have effects opposite to those of the well-known ‘original’ estrogen receptor (now called ER) challenges this simplistic view. In order to understand breast cancer one must first understand how the normal breast is maintained. The functions of ERβ in the breast remain to be defined but from what we have learnt about its activities in in vitro systems, this estrogen receptor may have a protective role in the breast. Studies in human and rodent breasts as well as in human breast cancer biopsies reveal that ERβ is by far the more abundant of the two ERs. Despite the role of estrogen in proliferation of the breast, neither of the two ERs appears to located in epithelial cells which divide in response to estrogen. In order to define the functions of ERβ in the normal and malignant breast, we have created mice in which the ERβ gene has been inactivated. Studies of the breasts of ERβ knock out mice (BERKO) revealed abnormal epithelial growth, overexpression of Ki67 and severe cystic breast disease as mice age.     

Presurgical (neoadjuvant) endocrine therapy is a useful model to predict response and outcome to endocrine treatment in breast cancer patients

Endocrine therapy of breast cancer has been improved continuously during the last decades. Currently, aromatase inhibitors are dominating treatment algorithms for postmenopausal women with hormone-receptor positive breast cancer while tamoxifen still is the most widely used drug for premenopausal women. Several research tools and study designs have been used to challenge established drugs and develop the field of antihormonal therapy. One pivotal study option has been the observation of clinical responses during presurgical/neoadjuvant endocrine therapy (PSET/NET). This strategy has several major advantages. First, the breast tumor, still present in the patient's breast during therapy, can be followed by clinical observations and radiological measurements and any treatment effect will be immediately registered. Second, tumor biopsies may be obtained before initiation and following therapy allowing intra-patient comparisons. These tumor-biopsies may be used for the evaluation of intra-tumor changes associated with drug treatment. As examples, presurgical breast cancer trials have been used to evaluate intra-tumor estrogen levels during therapy with aromatase inhibitors and also to study mechanisms involved in the adaptation processes to estrogen suppression. Biomarker studies have provided information that may be used for patient selection in the future. Finally, recently published results from presurgical trials testing combinations of classical endocrine drugs and novel targeted therapies have produced promising results.     

CB1 and CB2 receptors are novel molecular targets for Tamoxifen and 4OH-Tamoxifen

Tamoxifen (Tam) is classified as a selective estrogen receptor modulator (SERM) and is used for treatment of patients with ER-positive breast cancer. However, it has been shown that Tam and its cytochrome P450-generated metabolite 4-hydroxy-Tam (4OH-Tam) also exhibit cytotoxic effects in ER-negative breast cancer cells. These observations suggest that Tam and 4OH-Tam can produce cytotoxicity via estrogen receptor (ER)-independent mechanism(s) of action. The molecular targets responsible for the ER-independent effects of Tam and its derivatives are poorly understood. Interestingly, similar to Tam and 4OH-Tam, cannabinoids have also been shown to exhibit anti-proliferative and apoptotic effects in ER-negative breast cancer cells, and estrogen can regulate expression levels of cannabinoid receptors (CBRs). Therefore, this study investigated whether CBRs might serve as novel molecular targets for Tam and 4OH-Tam. We report that both compounds bind to CB1 and CB2Rs with moderate affinity (0.9–3 μM). Furthermore, Tam and 4OH-Tam exhibit inverse activity at CB1 and CB2Rs in membrane preparations, reducing basal G-protein activity. Tam and 4OH-Tam also act as CB1/CB2R-inverse agonists to regulate the downstream intracellular effector adenylyl cyclase in intact cells, producing concentration-dependent increases in intracellular cAMP. These results suggest that CBRs are molecular targets for Tam and 4OH-Tam and may contribute to the ER-independent cytotoxic effects reported for these drugs. Importantly, these findings also indicate that Tam and 4OH-Tam might be used as structural scaffolds for development of novel, efficacious, non-toxic cancer drugs acting via CB1 and/or CB2Rs.     

Do estrogens always increase breast cancer risk?

The etiology of breast cancer is closely linked to the female hormone estrogen, with high life-time exposure being suggested to increase breast cancer risk [Nature 303 (1983) 767]. However, there appears to be a disparity between studies attempting to establish an association between high estrogen levels and breast cancer risk. This disparity becomes smaller by taking into consideration a timing factor, and we propose that estrogens can increase, decrease, or have no effect on breast cancer risk, depending on the timing of estrogen exposure. We further propose that the timing of estrogenic exposures may play at least as important a role in affecting breast cancer risk as life-time exposure.     

Clinical practice guidelines for the care and treatment of breast cancer: 14. The role of hormone replacement therapy in women with a previous diagnosis of breast cancer

Objective

To provide information and recommendations to women with a previous diagnosis of breast cancer and their physicians regarding hormone replacement therapy (HRT).

Outcomes

Control of menopausal symptoms, quality of life, prevention of osteoporosis, prevention of cardiovascular disease, risk of recurrence of breast cancer, risk of death from breast cancer.

Evidence

Systematic review of English-language literature published from January 1990 to July 2001 retrieved from MEDLINE and CANCERLIT.

Recommendations

· Routine use of HRT (either estrogen alone or estrogen plus progesterone) is not recommended for women who have had breast cancer. Randomized controlled trials are required to guide recommendations for this group of women. Women who have had breast cancer are at risk of recurrence and contralateral breast cancer. The potential effect of HRT on these outcomes in women with breast cancer has not been determined in methodologically sound studies. However, in animal and in vitro studies, the development and growth of breast cancer is known to be estrogen dependent. Given the demonstrated increased risk of breast cancer associated with HRT in women without a diagnosis of breast cancer, it is possible that the risk of recurrence and contralateral breast cancer associated with HRT in women with breast cancer could be of a similar magnitude. · Postmenopausal women with a previous diagnosis of breast cancer who request HRT should be encouraged to consider alternatives to HRT. If menopausal symptoms are particularly troublesome and do not respond to alternative approaches, a well-informed woman may choose to use HRT to control these symptoms after discussing the risks with her physician. In these circumstances, both the dose and the duration of treatment should be minimized.

Validation

Internal validation within the Steering Committee on Clinical Practice Guidelines for the Care and Treatment of Breast Cancer; no external validation.

Sponsor

The steering committee was convened by Health Canada.

Completion date

October 2001.Hormone replacement therapy (HRT) connotes treatment with either estrogen alone or estrogen with progesterone in postmenopausal women. Menopausal symptoms, such as hot flashes and vaginal dryness, and the potential long-term effects of estrogen deprivation are a concern to women with breast cancer, particularly those in whom menopause develops early as a result of adjuvant chemotherapy.Traditionally, the use of HRT has been contraindicated in women with breast cancer because of the notion that the development and growth of breast cancer is estrogen dependent and that the introduction of HRT may increase the risk of breast cancer recurrence. The focus of this guideline is on whether it is safe to give HRT to women with breast cancer.     

Progress in the prevention of breast cancer: concept to reality

In 1936, Professor Antoine Lacassagne suggested that breast cancer could be prevented by developing drugs to block estrogen action in the breast. Jensen discovered the physiologic target, the estrogen receptor, that regulates estrogen action in its target tissues and Lerner discovered the first nonsteroidal antiestrogen MER25. However, the success of tamoxifen as a treatment of breast cancer opened the door for the testing of the worth of tamoxifen to reduce breast cancer incidence in high-risk women. In 1998, Fisher showed that tamoxifen could reduce breast cancer incidence by 50%. Nevertheless, only half the women who develop breast cancer have risk factors other than age, so what can be done for women without risk factors? The recognition that nonsteroidal antiestrogens have the ability to modulate estrogen action selectively has advanced the design and development of new drug for multiple diseases. Tamoxifen and raloxifene maintain bone density and raloxifene is now used to prevent osteoporosis and is being tested as a preventive for coronary heart disease and breast cancer. The drug group is now known as selective estrogen receptor modulators (SERMs) and the challenge is to design new agents for multiple applications. If the 20th century was the era of chemotherapy, the 21st century will be the era of chemoprevention.     

Up-regulation of PI3K/Akt signaling by 17beta-estradiol through activation of estrogen receptor-alpha, but not estrogen receptor-beta, and stimulates cell growth in breast cancer cells

Estrogen stimulates cell proliferation in breast cancer. The biological effects of estrogen are mediated through two intracellular receptors, estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta). However, the role of ERs in the proliferative action of estrogen is not well established. Recently, it has been known that ER activates phosphatidylinositol-3-OH kinase (PI3K) through binding with the p85 regulatory subunit of PI3K. Therefore, possible mechanisms may include ER-mediated phosphoinositide metabolism with subsequent formation of phosphatidylinositol-3,4,5-trisphosphate (PIP(3)), which is generated from phosphatidylinositol 4,5-bisphosphate via PI3K activation. The present study demonstrates that 17beta-estradiol (E2) up-regulates PI3K in an ERalpha-dependent manner, but not ERbeta, and stimulates cell growth in breast cancer cells. In order to study this phenomenon, we have treated ERalpha-positive MCF-7 cells and ERalpha-negative MDA-MB-231 cells with 10nM E2. Treatment of MCF-7 cells with E2 resulted in a marked increase in PI3K (p85) expression, which paralleled an increase in phospho-Akt (Ser-473) and PIP(3) level. These observations also correlated with an increased activity to E2-induced cell proliferation. However, these effects of E2 on breast cancer cells were not observed in the MDA-MB-231 cell line, indicating that the E2-mediated up-regulation of PI3K/Akt pathway is ERalpha-dependent. These results suggest that estrogen activates PI3K/Akt signaling through ERalpha-dependent mechanism in MCF-7 cells.     

Surgical Management for Early-Stage Bilateral Breast Cancer Patients in China

Background

The aim of this study was to investigate the current surgical management strategy for bilateral breast cancer (BBC) patients and to assess the changes in this strategy in China.

Methods

This is a retrospective review of all patients with early-stage BBC who underwent surgical treatment at the Fudan University Shanghai Cancer Center between June 2007 and June 2014.

Results

A total of 15,337 patients with primary breast cancer were identified. Of these patients, 218 (1.5%) suffered from synchronous bilateral breast cancer (sBBC), and 296 (2.0%) suffered from metachronous bilateral breast cancer (mBBC). Patients with a lobular carcinoma component, those with estrogen receptor-positive cancer, and those with an accompanying sclerosing adenosis in the affected breast tended to develop BBC. The rates of bilateral mastectomy, breast conserving therapy, reconstruction, and combined surgeries were 86.2%, 6.4%, 3.7%, and 3.7%, respectively, for patients with sBBC and 81.1%, 4.4%, 3.0%, and 11.5%, respectively, for patients with mBBC. The interval between bilateral cancers, age at first diagnosis of breast cancer, histopathological type, and stage have significant impacts on the choice of surgery for patients with BBC.

Conclusions

Bilateral mastectomy was the dominant surgical management for patients with BBC in China, despite the increased application of breast reconstruction surgery observed in recent years. Bilateral prosthetic breast reconstruction was the ideal choice for patients with sBBC. Chinese surgeons should take responsibility for patient education and inform their patients about their surgical options.     

Inhibition of aromatase: insights from recent studies

Aromatase is the rate limiting enzyme that catalyzes the conversion of androgens to estrogens. Blockade of this step allows treatment of diseases that are dependent upon estrogen. Over the past two decades, highly potent and specific aromatase inhibitors have been developed which block total body aromatization by over 99%. An important recent question is whether aromatase inhibitors are superior to the antiestrogens for treatment of hormone-dependent breast cancer. The third generation aromatase inhibitors have been compared to tamoxifen for the treatment of breast cancer in the advanced, adjuvant, and neoadjuvant settings. All of these studies suggest the superiority of aromatase inhibitors over tamoxifen. The mechanism responsible for the superiority of the aromatase inhibitors relates to the estrogen agonistic effects of tamoxifen. During exposure to estrogen deprived conditions and to tamoxifen, breast cancer cells adapt and upregulate the MAP kinase and PI-3 kinase pathways. These growth factor signaling pathways potentiate the estrogen agonistic properties of tamoxifen. Data from a large adjuvant therapy trial (ATAC trial) provide evidence that the aromatase inhibitors may also be superior for breast cancer prevention. The mechanism for superiority in this setting probably relates to the genotoxic effects of estradiol metabolites. The aromatase inhibitors may be also useful for the treatment of endometriosis and for ovulation induction as evidenced by preliminary data. The recent advances in development of the aromatase inhibitors clearly demonstrate the utility of these agents for treatment of breast cancer and potentially for other indications.     

Aromatase inhibitors: future directions

Estrogen and its cognate estrogen receptor are key players in the etiology and progression of breast cancer. Aromatase inhibitors, suppressing tumor and plasma estrogen levels by blocking testosterone conversion to estrogen, have been proven to provide the most effective endocrine therapy for postmenopausal breast cancer patients. Aromatase inhibitors are now the first choice endocrine therapy in the metastatic setting for postmenopausal women. These endocrine agents also seem likely to soon become the standard adjuvant therapy, either alone or in sequence with tamoxifen, though their long-term toxicity and the optimum duration of therapy still remain to be defined. Advanced experimental studies and some clinical observations reveal the importance of blocking both the genomic and non-genomic activities of the estrogen receptor, as well as its crosstalk with growth factor and other cellular signaling, for greatest effectiveness of endocrine therapy. Consequently, these studies provide a mechanistic explanation for the superb performance of aromatase inhibitors, and also suggest how inhibiting selected growth factor receptors might delay or prevent the onset of resistance to aromatase inhibitors and other endocrine therapies.     

Risk of breast cancer with progestins: critical assessment of current data

Whether progestins protect against the risk of breast cancer or enhance that risk has been a major area of controversy over the past several years. Observational studies have reported conflicting results and experimental studies examining whether progestins exert mitogenic or anti-mitogenic actions on breast tissue report divergent results. Based upon a wide range of animal, epidemiologic and clinical data, most investigators agree that estrogens contribute to the development of breast neoplasms. However, the additional effect of progestins on this risk has been the subject of substantial discussion and controversy. A variety of experiments have been carried out using human breast cancer cells grown in vitro and as xenografts in nude mice. These studies demonstrated both mitogenic and anti-mitogenic effects depending upon the precise experimental conditions. Two potential reasons for these differences include differential metabolism of progestins into inhibitory pregnenes or stimulatory 5-alpha-reduced pregnanes or the presence of a protein (GPR 30) which allows the anti-mitogenic effects of progestins to be manifest. Based upon the conflicting nature of the results in experimental studies, we believe that only data in patients provide substantial insight into the actions of progestins on the intact human breast. Studies have now demonstrated that cell proliferation and breast density is higher during the luteal than during the follicular phase of the menstrual cycle. In postmenopausal women, long-term exposure to estrogen plus a progestin results in a marked enhancement of proliferation of the terminal duct lobular units as well as in breast density. These data, taken together, provide substantial evidence that progestins are mitogenic on the human breast when given long term to postmenopausal women. To critically evaluate the observational studies regarding breast cancer risk from progestins, we developed a set of stringent criteria for acceptance of individual studies. Four of the five studies meeting these criteria reported a greater risk of breast cancer with combination estrogen/progestin regimens than with estrogen alone. More importantly, the first randomized, prospective, controlled trial of the risk of breast cancer with an estrogen/progestin combination (the Women's Health Initiative Study) has now been published. This study reported a 26% increased relative risk of breast cancer with the estrogen/progestin combination. Based upon these data, we believe that progestins do add to the risk of breast cancer over and above that imparted by estrogen alone. The attributable risk during use for 5 years or less is small but increases logarithmically during long-term use. The majority of data regarding progestins are derived from regimens using MPA. However, we conclude from our analysis that the burden of proof regarding progestins has now shifted. One must now prove that an estrogen/progestin combination is safe with respect to breast cancer rather than having to prove it harmful.     

Menopausal hormone therapy and cancer: Changing clinical observations of target site specificity

Menopausal hormone therapy with estrogen plus progestin or estrogen alone (for women with prior hysterectomy) is still used by millions of women for climacteric symptom management throughout the world. Until 2002, hormone therapy influence on cancer risk and other chronic diseases was determined through observational study reports. Since then, results from the Women’s Health Initiative randomized, placebo-controlled hormone therapy trials have substantially changed concepts regarding estrogen plus progestin and estrogen alone influence on the most common cancers in postmenopausal women. In these trials, estrogen plus progestin significantly increased breast cancer incidence and deaths from breast cancer, significantly increased deaths from lung cancer, significantly decreased endometrial cancer, and did not have a clinically significant influence on colorectal cancer. In contrast, estrogen alone use in women with prior hysterectomy significantly reduced breast cancer incidence and deaths from breast cancer without significant influence on colorectal cancer or lung cancer. These complex results are discussed in the context of known potential mediating mechanisms of action involved in interaction with steroid hormone receptors.