Hormones and cancer in humans

Hormones play a major role in the aetiology of several of the commonest cancers worldwide, including cancers of the endometrium, breast and ovary in women and cancer of the prostate in men. It is likely that the main mechanisms by which hormones affect cancer risk are by controlling the rate of cell division, the differentiation of cells and the number of susceptible cells. Hormones have very marked effects on cell division in the endometrium; oestrogens stimulate mitosis whereas progestins oppose this effect. The risk for endometrial cancer increases with late menopause, oestrogen replacement therapy and obesity, and decreases with parity and oral contraceptive use; thus risk increases in proportion to the duration of exposure to oestrogens unopposed by progestins, probably because unopposed oestrogens stimulate endometrial cell division. The effects of hormones on breast epithelial cell division in non-pregnant women are much less clear-cut than their effects on the endometrium, but both oestrogens and progestins appear to stimulate mitosis. Breast cancer risk increases with early menarche, late menopause and oestrogen replacement therapy, probably due to increased exposure of the breasts to oestrogen and/or progesterone. Early first pregnancy and multiparity reduce the risk for breast cancer, probably due to the hormonally-induced differentiation of breast cells and the corresponding reduction in the number of susceptible cells. Hormones do not have marked direct effects on the epithelial cells covering the ovaries, but hormones stimulate ovulation which is followed by cell division during repair of the epithelium. Risk for ovarian cancer increases with late menopause and decreases with parity and oral contraceptive use, suggesting that the lifetime number of ovulations may be a determinant of risk. For all three of these cancers risk changes within a few years of changes in exposure to sex hormones and some of the changes in risk persist for many years, indicating that hormones can affect both early and late stages of carcinogenesis. Understanding of the role of sex hormones in the aetiology of prostate cancer and of some rarer cancers is less complete.     

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.     

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".     

Aromatization inhibition alone or in combination with GnRH agonists for the treatment of premenopausal breast cancer patients.

Aromatase inhibition in postmenopausal women causes a marked fall in the plasma levels of oestrogens and is an effective treatment for breast cancer, however, trials with aminoglutethimide found that this aromatase inhibitor was ineffective in suppressing plasma oestrogen levels in premenopausal breast cancer patients. We found that the more potent inhibitor, 4-hydroxyandrostenedione (4-OHA), which can suppress oestrogen synthesis in rodents and non-human primates with intact ovarian function, was also unsuccessful as an oestrogen suppressant in premenopausal women at its maximum tolerated dose (500 mg/week i.m.). GnRH agonists are effective suppressants of ovarian oestrogen synthesis but oestrogen production from peripheral sites is unaffected. Our studies of a combination of the GnRH agonist goserelin and 4-OHA demonstrated that the combination caused greater oestrogen suppression than goserelin alone and led to objective clinical response in 4/6 breast cancer patients after their relapse from treatment with goserelin as a single agent. The combination of a GnRH agonist and an aromatase inhibitor should be subjected to clinical trials.     

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.     

Local uptake and synthesis of oestrone in normal and malignant postmenopausal breast tissues

Uptake and local formation of oestrone (E1) were studied in vivo by a double isotopic technique in normal and malignant breast tissues from 24 postmenopausal women with breast cancer. Active uptake of radio-labelled E1 beyond plasma was found both in normal and malignant tissue, the effect being significantly greater in non-malignant compared with cancer tissue. The presence of local E1 formation was also demonstrated in most samples. Both uptake and synthesis positively correlated with total amount of radioactive E1 found in the tissues. Uptake appeared to make a greater contribution to E1 levels within the breast than in situ synthesis, although there were marked variations between specimens from different patients and the relative proportion of synthesis to uptake was higher in tumour compared with non-malignant tissue. These results demonstrate quantitative differences in the different compartments by which postmenopausal breasts obtain oestrogen and highlight variations between individual breasts. This may be important in optimising oestrogen deprivation therapy for postmenopausal patients with hormone-dependent cancers.     

Local endocrine effects of aromatase inhibitors within the breast

To determine the effects of aromatase inhibitors on oestrogen uptake, in situ aromatase activity and endogenous oestrogens in the breast, postmenopausal women with large primary ER-rich breast cancers have been treated neoadjuvantly for 3 months with either letrozole (2.5 or 10 mg daily) or anastrozole (1 or 10 mg daily) or exemestane (25 mg daily). Patients were given an infusion of ³H-androstenedione and ¹⁴C-oestrone for 18 h before and at the end of the study period. Blood, tumour and non-malignant breast were taken immediately after each infusion; oestrogens were extracted and purified. Tumour volume was measured before and during treatment at monthly intervals so that endocrinological changes could be related to clinical response. Treatment with each of the aromatase inhibitors was associated with a profound reduction in peripheral aromatase (as monitored by the level of plasma ³H-oestrone). There was no consistent effect on uptake of radioactively labelled oestrogen into breast tumours but a tendency for levels to increase after treatment in non-malignant breast. Conversely, therapy was associated with a marked inhibition of in situ oestrogen synthesis in both tumour and non-malignant breast (in occasional tissues, inhibitors appeared to be less effective but the effect was not related to clinical or pathological responses). Similar decreases were apparent in endogenous levels of oestrone and oestradiol. The absence of in situ aromatase activity tended to be associated with lack of clinical response to aromatase inhibition but the relationship was not absolute, limiting the utility of measurements of tumour aromatase as a predictive indices. Ex vivo studies of tissue aromatase indicated that such measurements consistently underestimate the inhibitory potential of reversible non-steroidal agents (and occasionally paradoxical in vitro increases in aromatase activity were seen with treatment). However, in situ assays demonstrate that new aromatase inhibitors such as anastrozole, exemestane and letrozole have profound effects on the local endocrinology within the postmenopausal breast, these being compatible with the clinico-pathological changes which occur with treatment.     

Molecular epidemiology of breast cancer: genetic variation in steroid hormone metabolism

The age-specific incidence rate of breast cancer in women rises until menopause, levels off and then rises again at a much lower rate indicating a possible hormonal influence on the disease risk. A large amount of evidence has implicated hormones and other compounds with oestrogen activity in the pathogenesis of certain endocrine cancers, particularly breast cancer. Widely dispersed hormone-like chemicals, capable of disrupting the endocrine system and interfering with proliferation, have been described. Compounds such as dioxins, some polychlorinated biphenyls and the plastic ingredient bisphenol-A have been shown to interfere with human reproduction and hormonal regulation. The levels of these foreign compounds as well as the levels of endogenous oestradiol may influence the risk of breast cancer. Endogenous oestradiol is synthesised 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 cancer tissue, express all the necessary enzymes for this synthesis: CYP17, CYP11a, CYP19, hydroxysteroid hydrogenase, steroid sulphatase as well as enzymes further hydroxylating oestradiol such as CYP1A1, CYP3A4, CYP1B1. 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.     

Reduction in serum IL-6 after vacination of breast cancer patients with tumour-associated antigens is related to estrogen receptor status

Elevated serum IL-6 concentrations have been associated with poor prognosis in a variety of cancers, and decreases in serum IL-6 concentrations have been reported after chemotherapy. We have demonstrated that serum IL-6 concentrations are elevated in breast cancer patients [normal women 0.7 +/- 2.5 pg/ml (n=36), breast cancer patients 38.3 +/- 138.7 pg/ml (n = 111)]. After vaccination of breast cancer patients with a combination of tumour-associated antigens and biological adjuvants (IL-2 and GM-CSF), the concentration of IL-6 decreased significantly (P<0.05) to 8.1 +/- 14.6 pg/ml (n=85). Other studies have shown that oestrogen suppresses IL-6 production in oestrogen receptor positive breast cancer cells. We have demonstrated that the decrease in IL-6 associated with vaccination is related to the oestrogen receptor status of the tumours from breast cancer patients, as a decrease in IL-6 from 124.0 +/- 267.5 pg/ml (n=26) to 6.2 +/- 11.0 pg/ml (n=34) only occurs in patients with oestrogen receptor negative tumours. The IL-6 concentration in breast cancer patients with oestrogen receptor positive tumours remained unchanged (9.5 pg/ml before vaccination, and 9.3 pg/ml after vaccination). These results suggest that postmenopausal women with oestrogen receptor negative breast cancers, who do not respond well to either hormonal therapy with tamoxifen or adjuvant chemotherapy, may have a significant response to vaccination with autologous tumour-associated antigens.     

Exemestane,a new steroidal aromatase inhibitor of clinical relevance

Breast cancer is the leading cause of death among women and the contribution of circulating oestrogens to the growth of some mammary tumours has been recognized. Consequently, suppression of oestrogen action by inhibition of their biosynthesis at the androstenedione-oestrone aromatization step, by means of selective inhibitors of the enzyme aromatase, has become an effective therapeutic option for the treatment of hormone-dependent breast cancer. Exemestane (6-methylenandrosta-1,4-diene-3,17-dione) is a novel steroidal irreversible aromatase inhibitor recently approved and introduced into the global market under the name Aromasin. The design, laboratory and viable syntheses of exemestane, starting from a variety of steroidal precursors, are presented and discussed. Data from biochemical and pharmacological studies as well as the clinical impact of the compound are briefly reviewed. The drug is an orally active and well-tolerated hormonal therapy for postmenopausal patients with advanced breast cancer that has become refractory to standard current hormonal therapies.     

Specific expression of human pS2 gene in breast cancer

The hormone-dependence of some human breast cancers is well recognized. However, the molecular mechanisms responsible for the growth stimulation of these cancers by oestrogens are still poorly understood. With the hope of elucidating these mechanisms, we have recently cloned and studied the structure-function relationship of the human oestrogen and progestin receptors, and also undertaken a study aimed at characterizing genes whose expression is controlled by oestrogens in hormone-dependent breast cancers. We review here our findings concerning one of these genes and its expression products, the pS2 gene. We discuss also whether a systematic determination of pS2 gene expression in breast cancer biopsies could be useful to establish a new biochemical classification of these cancers which may be useful to improve the diagnosis of hormone-dependent cancers.     

Frequent chest X-ray fluoroscopy and breast cancer incidence among tuberculosis patients in Massachusetts

The incidence of breast cancer was determined in 4940 women treated for tuberculosis between 1925 and 1954 in Massachusetts. Among 2573 women examined by X-ray fluoroscopy an average of 88 times during lung collapse therapy and followed for an average of 30 years, 147 breast cancers occurred in contrast to 113.6 expected [observed/expected (O/E) = 1.29; 95% confidence interval (CI) = 1.1-1.5]. No excess of breast cancer was seen among 2367 women treated by other means: 87 observed versus 100.9 expected. Increased rates for breast cancer were not apparent until about 10 to 15 years after the initial fluoroscopy examination. Excess risk then remained high throughout all intervals of follow-up, up to 50 years after first exposure. Age at exposure strongly influenced the risk of radiation-induced breast cancer with young women being at highest risk and those over age 40 being at lowest risk [relative risk (RR) = 1.06]. Mean radiation dose to the breast was estimated to be 79 cGy, and there was strong evidence for a linear relationship between dose and breast cancer risk. Allowing for a 10-year minimum latent period, the relative risk at 1 Gy was estimated as 1.61 and the absolute excess as 10.7 per 10(4) woman-years per gray. When compared to other studies, our data suggest that the breast is one of the most sensitive tissues to the carcinogenic force of radiation, that fractionated exposures are similar to single exposures of the same total dose in their ability to induce breast cancer, that risk remains high for many years after exposure, and that young women are especially vulnerable to radiation injury.     

Factors influencing aromatase activity in the breast

Particularly in postmenopausal women, peripheral aromatase appears to be the major source of oestrogens which may encourage the growth of hormone-dependent tumours. Studies have therefore been undertaken to determine factors which influence biosynthesis of oestrogens within breast tissues. Aromatase activity was measured in (i) breast cancers by incubating tumour homogenates with [7³H]testosterone and characterizing the production of radioactively-labelled oestradiol and (ii) breast fat by incubation of sub-cellular fractions of fibroblast cell lines with [1ß³H]androstenedione and monitoring the formation of ³H₂O. Evidence has been presented that (i) certain treatment regimes for cancer profoundly influence aromatase activity in breast tumours, (ii) aromatase activity is elevated in breast fat associated with malignancy and (iii) breast-derived fluids and extracts can markedly affect aromatase activity in cultured fibroblasts of breast fat.     

Case-control study of oestrogen replacement therapy and risk of cervical cancer.

OBJECTIVE: To examine the relation between use of oestrogen replacement therapy and risk of cervical cancer. DESIGN: Case-control study. SETTING: Northern Italy. SUBJECTS: 645 women aged 40-75 years with cervical cancer admitted between 1981 and 1993 to university and general hospitals. The control group consisted of 749 women aged 40-75 years admitted to the same hospitals with acute conditions judged to be unrelated to any of the known or suspected risk factors for cervical cancer. MAIN OUTCOME MEASURES: Use of oestrogen replacement therapy and risk of cervical cancer. RESULTS: 40 cases versus 86 controls had ever used oestrogens, and the corresponding multivariate odds ratio was 0.5 (95% confidence interval 0.3 to 0.8). The odds ratios of cervical cancer decreased with duration of use, being 0.6 (0.4 to 1.1) for less than 12 months'' use and 0.5 (0.2 to 1.0) for use for 12 months or more compared with never users. The protection tended to be somewhat stronger for women reporting first oestrogen use before age 50. The odds ratio was 0.9 (0.5 to 1.7) for women who had taken oestrogens within the past 10 years and 0.4 (0.2 to 0.7) for those who had taken them 10 or more years ago. CONCLUSION: These findings suggest that exogenous oestrogens do not increase the risk of cervical cancer and may decrease the risk.     

Cancer incidence and mortality in relation to body mass index in the Million Women Study: cohort study

Objective To examine the relation between body mass index (kg/m²) and cancer incidence and mortality.Design Prospective cohort study.Participants 1.2 million UK women recruited into the Million Women Study, aged 50-64 during 1996-2001, and followed up, on average, for 5.4 years for cancer incidence and 7.0 years for cancer mortality.Main outcome measures Relative risks of incidence and mortality for all cancers, and for 17 specific types of cancer, according to body mass index, adjusted for age, geographical region, socioeconomic status, age at first birth, parity, smoking status, alcohol intake, physical activity, years since menopause, and use of hormone replacement therapy.Results 45 037 incident cancers and 17 203 deaths from cancer occurred over the follow-up period. Increasing body mass index was associated with an increased incidence of endometrial cancer (trend in relative risk per 10 units=2.89, 95% confidence interval 2.62 to 3.18), adenocarcinoma of the oesophagus (2.38, 1.59 to 3.56), kidney cancer (1.53, 1.27 to 1.84), leukaemia (1.50, 1.23 to 1.83), multiple myeloma (1.31, 1.04 to 1.65), pancreatic cancer (1.24, 1.03 to 1.48), non-Hodgkin''s lymphoma (1.17, 1.03 to 1.34), ovarian cancer (1.14, 1.03 to 1.27), all cancers combined (1.12, 1.09 to 1.14), breast cancer in postmenopausal women (1.40, 1.31 to 1.49) and colorectal cancer in premenopausal women (1.61, 1.05 to 2.48). In general, the relation between body mass index and mortality was similar to that for incidence. For colorectal cancer, malignant melanoma, breast cancer, and endometrial cancer, the effect of body mass index on risk differed significantly according to menopausal status.Conclusions Increasing body mass index is associated with a significant increase in the risk of cancer for 10 out of 17 specific types examined. Among postmenopausal women in the UK, 5% of all cancers (about 6000 annually) are attributable to being overweight or obese. For endometrial cancer and adenocarcinoma of the oesophagus, body mass index represents a major modifiable risk factor; about half of all cases in postmenopausal women are attributable to overweight or obesity.     

The role and proposed mechanism by which oestradiol 17β-hydroxysteroid dehydrogenase regulates breast tumour oestrogen concentrations

Synthesis of the biologically active oestrogen, oestradiol, within breast tumours makes an important contribution to the high concentrations of oestrogens which are present in malignant breast tissues. In breast tumours, oestrone is preferentially converted to oestradiol by the Type I oestradiol 17β-hydroxysteroid dehydrogenase (E2DH). Several growth factors, such as insulin-like growth factor Type I, and cytokines, such as Tumour Necrosis Factor (TNF), have been shown to stimulate E2DH activity in MCF-7 breast cancer cells. As little is known about the regulation of Type I E2DH expression and activity in other breast cancer cell lines, the expression and activity of this enzyme was examined in other oestrogen receptor positive and also oestrogen receptor negative breast cancer cell lines. As it is possible that E2DH activity may be limited by co-factor availability, the effects of exogenous co-factors on enzyme activity in these cell lines was also investigated. For T47D and BT20 breast cancer cells, the addition of exogenous co-factors was found to enhance enzyme activity. TNF, in addition to stimulating E2DH activity in MCF-7 cells, also increased activity in T47D and MDA-MB-231 cells, although to a lesser extent than in MCF-7 cells. An investigation of signalling pathways involved in the regulation of E2DH activity revealed that stimulation of both the protein kinase C (PKC) and PKA pathways may be involved in regulation of E2DH activity. As several growth factors and cytokines have now been found to be involved in regulating E2DH activity, the role that macrophages and lymphocytes have in supplying these factors and the mechanism by which these factors may stimulate tumour growth, is also reviewed.     

Aromatase, aromatase inhibitors, and breast cancer

Estrogens are known to be important in the growth of breast cancers in both pre and postmenopausal women. As the number of breast cancer patients increases with age, the majority of breast cancer patients are postmenopausal women. Although estrogens are no longer made in the ovaries after menopause, peripheral tissues produce sufficient concentrations to stimulate tumor growth. As aromatase catalyzes the final and rate-limiting step in the biosynthesis of estrogen, inhibitors of this enzyme are effective targeted therapy for breast cancer. Three aromatase inhibitors (AIs) are now FDA approved and have been shown to be more effective than the antiestrogen tamoxifen and are well tolerated. AIs are now a standard treatment for postmenopausal patients. AIs are effective in adjuvant and first-line metastatic setting. This review describes the development of AIs and their current use in breast cancer. Recent research focuses on elucidating mechanisms of acquired resistance that may develop in some patients with long term AI treatment and also in innate resistance. Preclinical data in resistance models demonstrated that the crosstalk between ER and other signaling pathways particularly MAPK and PI3K/Akt is an important resistant mechanism. Blockade of these other signaling pathways is an attractive strategy to circumvent the resistance to AI therapy in breast cancer. Several clinical trials are ongoing to evaluate the role of these novel targeted therapies to reverse resistance to AIs. Article from the special issue on 'Targeted Inhibitors'.     

Oestrogen receptors and survival in early breast cancer.

Oestrogen receptor status was related to survival in 414 patients with primary breast cancer. Women with oestrogen receptors in their tumours survived significantly longer than those without receptors; this was true for both premenopausal and postmenopausal women and also when the patients were subdivided into those with and without axillary metastases. Patients with axillary metastases and no oestrogen receptors in their tumours had the worst prognosis, while women with axillary metastases and oestrogen receptors had a death rate similar to that of women with no axillary metastases and no receptors. Patients without oestrogen receptors and with no axillary metastases were identified as a high-risk group, and it would seem appropriate to include such patients in future trials for adjuvant therapy in early breast cancer.     

Cardioprotective effect of hormone replacement therapy in postmenopausal women: is the evidence biased?

OBJECTIVE--To quantify the effect of selection of relatively healthy women in studies reporting reduced relative risk for cardiovascular disease in postmenopausal women taking hormone replacement therapy. DESIGN--Review of the follow up studies reported in three recent meta-analyses to determine the effect of oestrogen therapy on both total cancer and cardiovascular disease. The same standard statistical methods as in the original analyses were used. MAIN OUTCOME MEASURES--Relative risks of total cancer and cardiovascular disease. RESULTS--In most of the follow up studies the relative risk for total cancer was below 1. The studies that showed the largest reduction in cardiovascular disease also showed the largest reduction in cancer, indicating a healthy cohort effect. Although heterogeneity within the studies prevented pooling, the best estimate for the protective effect on total cancer was a relative risk of 0.83 among women taking oestrogen (95% confidence interval 0.71 to 0.96), while in the same studies the relative risk for cardiovascular disease was 0.57 (0.50 to 0.64). CONCLUSIONS--Unintended selection of relatively healthy women for oestrogen therapy may have influenced the reported beneficial effect of oestrogen therapy on cardiovascular disease. It is unclear how much of the cardioprotection is due to this selection. Universal preventive hormonal replacement therapy for postmenopausal women is unwarranted at present.