Potential impact on breast cancer risk of circulating insulin-like growth factor I modifications induced by oral HRT in menopause

Growth Hormone/Insulin Growth Factor Axis in Sex Steroid Associated Disorders and Related Cancers

To date, almost all solid malignancies have implicated insulin-like growth factor (IGF) signalling as a driver of tumour growth. However, the remarkable level of crosstalk between sex hormones, the IGF-1 receptor (IGF-1R) and its ligands IGF-1 and 2 in endocrine driven cancers is incompletely understood. Similar to the sex steroids, IGF signalling is essential in normal development as well as growth and tissue homoeostasis, and undergoes a steady decline with advancing age and increasing visceral adiposity. Interestingly, IGF-1 has been found to play a compensatory role for both estrogen receptor (ER) and androgen receptor (AR) by augmenting hormonal responses in the absence of, or where low levels of ligand are present. Furthermore, experimental, and epidemiological evidence supports a role for dysregulated IGF signalling in breast and prostate cancers. Insulin-like growth factor binding protein (IGFBP) molecules can regulate the bioavailability of IGF-1 and are frequently expressed in these hormonally regulated tissues. The link between age-related disease and the role of IGF-1 in the process of ageing and longevity has gained much attention over the last few decades, spurring the development of numerous IGF targeted therapies that have, to date, failed to deliver on their therapeutic potential. This review will provide an overview of the sexually dimorphic nature of IGF signalling in humans and how this is impacted by the reduction in sex steroids in mid-life. It will also explore the latest links with metabolic syndromes, hormonal imbalances associated with ageing and targeting of IGF signalling in endocrine-related tumour growth with an emphasis on post-menopausal breast cancer and the impact of the steroidal milieu.

Differential effects of various progestogens on metabolic risk factors for breast cancer

Biological and epidemiological findings suggest that metabolic factors - insulin, insulin-like growth factor-I (IGF-I) and sex hormone-binding globulin (SHBG) - are involved in the development and promotion of breast cancer. Estrogens, particularly if administered orally, counteract metabolic factors that increase breast cancer risk, i.e. they reduce insulin and IGF-I and increase SHBG. This could contribute toward explaining epidemiological data showing that unopposed oral estrogens do not increase breast cancer risk, or do so only modestly. In contrast to natural progesterone and progesterone-derived progestins, progestins endowed with androgenic (or glucocorticoid) activity negatively influence these metabolic factors, counteracting the favorable effects of estrogens. While most biological and epidemiological findings suggest that natural progesterone does not augment breast cancer risk, available data show an increased risk with synthetic progestins - with the possible exception of progesterone-derived dydrogesterone. Different mechanisms for different progestins could possibly be involved. Differences from progesterone with regard to pharmacokinetics and pharmacodynamics, potency, interaction with the two isoforms of the progesterone receptor, and binding to other steroid receptors could all be relevant. These remain theoretical speculations for the time being, but the possibility that some progestins increase breast cancer risk through their negative influence on metabolic factors cannot be rejected.

Oral 17beta-estradiol and sequential progesterone in menopause: effects on insulin-like growth factors and their binding proteins

OBJECTIVE

We evaluated the acute effects of low-dose oral estradiol and sequential progesterone on the insulin-like growth factor (IGF)/growth hormone (GH) axis, IGF-binding proteins (IGFBPs) 1 and 3, and plasma levels of sex hormone-binding globulin (SHBG) in postmenopausal subjects.

STUDY DESIGN

Thirty healthy normal-weight women (mean age: 54.2 +/- 5.7 years) spontaneously postmenopausal for at least 6 months were enrolled. None had used hormone replacement therapy (HRT). Appropriate investigations excluded renal, glucose, lipid and coagulation abnormalities. Breast X-ray and endometrial ultrasound examinations excluded organic pathologies. They received oral cyclical HRT for 1 year, based on the administration of oral estradiol (1 mg/day) for 28 consecutive days plus progesterone (200 mg/day) from day 15 to day 28; out of the whole group, 15 subjects received progesterone orally (group A), while in 15 progesterone was administered transvaginally (group B). On the day before treatment (T0), on day 14 (T14) and on day 28 (T28) of the first cycle, plasma levels of estradiol, progesterone, SHBG, GH, IGF-I and -II, IGFBP-1 and -3, insulin and C-peptide were assayed in all patients. The same parameters were evaluated at T14 and T28 during the 12th month of treatment.

RESULTS

At T14, we observed significant increases in the levels of estradiol (from 20 +/- 16 to 115 +/- 71 pg/ml, p < 0.001), SHBG (from 132 +/- 42 to 182 +/- 55 nmol/l, p < 0.001) and IGFBP-1 (from 92 +/- 57 to 127 +/- 87 ng/ml, p < 0.004), while the level of IGF-I decreased (from 197 +/- 138 to 129 +/- 85 ng/ml, p < 0.003). At T28, progesterone levels were significantly higher in the women receiving it orally than transvaginally (8.4 +/- 6.1 vs. 3.7 +/- 3.2 ng/ml, p < 0.025). However, while oral progesterone did not affect the estrogen-induced variations, transvaginal progesterone abrogated the increase in the levels of IGFBP-1. The levels of IGF-II, IGFBP-3, GH, glucose, C-peptide and insulin did not change at any time. At 1 year, the values maintained the same trends. The estrogen-induced variations of SHBG were correlated directly with those of estradiol (r = 0.48) and inversely with those of IGF-I (r = -0.424).

CONCLUSIONS

Low-dose oral estradiol reduces plasma levels of IGF-I and increases IGFBP-1 and SHBG concentrations, while GH is unchanged. These effects, significant and immediate, lead us to hypothesize a direct action of estradiol on hepatocytes.

Pregnancy, progesterone and progestins in relation to breast cancer risk

In the last two decades the prevailing opinion, supported by the "estrogen augmented by progesterone" hypothesis, has been that progesterone contributes to the development of breast cancer (BC). Support for this opinion was provided by the finding that some synthetic progestins, when added to estrogen in hormone replacement therapy (HRT) for menopausal complaints, increase the BC risk more than estrogen alone. However, recent findings suggest that both the production of progesterone during pregnancy and the progesterone endogenously produced or exogenously administered outside pregnancy, does not increase BC risk, and could even be protective. The increased BC risk found with the addition of synthetic progestins to estrogen in HRT seems in all likelihood due to the fact that these progestins (medroxyprogesterone acetate and 19-nortestosterone-derivatives) are endowed with some non-progesterone-like effects which can potentiate the proliferative action of estrogens. The use of progestational agents in pregnancy, for example to prevent preterm birth, does not cause concern in relation to BC risk.

Progestins and progesterone in hormone replacement therapy and the risk of breast cancer

Controlled studies and most observational studies published over the last 5 years suggest that the addition of synthetic progestins to estrogen in hormone replacement therapy (HRT), particularly in continuous-combined regimen, increases the breast cancer (BC) risk compared to estrogen alone. By contrast, a recent study suggests that the addition of natural progesterone in cyclic regimens does not affect BC risk. This finding is consistent with in vivo data suggesting that progesterone does not have a detrimental effect on breast tissue. The increased BC risk found with the addition of synthetic progestins to estrogen could be due to the regimen and/or the kind of progestin used. Continuous-combined regimen inhibits the sloughing of mammary epithelium that occurs after progesterone withdrawal in a cyclic regimen. More importantly, the progestins used (medroxyprogesterone acetate and 19-Nortestosterone-derivatives) are endowed with some non-progesterone-like effects, which can potentiate the proliferative action of estrogens. Particularly relevant seem to be the metabolic and hepatocellular effects (decreased insulin sensitivity, increased levels and activity of insulin-like growth factor-I, and decreased levels of SHBG), which contrast the opposite effects induced by oral estrogen.

Breast cancer risk in relation to different types of hormone replacement therapy in the E3N-EPIC cohort

Most epidemiological studies have shown an increase in breast cancer risk related to hormone replacement therapy (HRT) use. A recent large cohort study showed effects of similar magnitude for different types of progestogens and for different routes of administration of estrogens evaluated. Further investigation of these issues is of importance. We assessed the risk of breast cancer associated with HRT use in 54,548 postmenopausal women who had never taken any HRT 1 year before entering the E3N-EPIC cohort study (mean age at inclusion: 52.8 years); 948 primary invasive breast cancers were diagnosed during follow-up (mean duration: 5.8 years). Data were analyzed using multivariate Cox proportional hazards models. In this cohort where the mean duration of HRT use was 2.8 years, an increased risk in HRT users compared to nonusers was found (relative risk (RR) 1.2 [95% confidence interval 1.1-1.4]). The RR was 1.1 [0.8-1.6] for estrogens used alone and 1.3 [1.1-1.5] when used in combination with oral progestogens. The risk was significantly greater (p <0.001) with HRT containing synthetic progestins than with HRT containing micronized progesterone, the RRs being 1.4 [1.2-1.7] and 0.9 [0.7-1.2], respectively. When combined with synthetic progestins, both oral and transdermal/percutaneous estrogens use were associated with a significantly increased risk; for transdermal/percutaneous estrogens, this was the case even when exposure was less than 2 years. Our results suggest that, when combined with synthetic progestins, even short-term use of estrogens may increase breast cancer risk. Micronized progesterone may be preferred to synthetic progestins in short-term HRT. This finding needs further investigation.

Progestins and their effects on the breast

Nowadays, when the available scientific data on the in vivo effects of progestins on mammary gland tissue remain controversial, it is of utmost importance to establish adequate criteria to evaluate their actions. One of the reasons for this situation is that a variety of progestins have been studied using a number of different study designs. In addition, data relating to the effects of progestins on breast tissue have been interpreted differently from country to country. Recent data indicate that some progestins clearly oppose the favourable effects of estrogens on a number of important metabolic processes, e.g. influencing insulin-like-growth-factor (IGF)-1 serum levels. IGF-1 is a mitogenic and antiapoptotic peptide involved in growth regulation of breast epithelial cells. Circulating IGF-1 exerts endocrine action, it regulates growth hormone secretion by a negative feedback mechanism. In the past few years, both laboratory investigations and epidemiologic studies provided strong evidence that the IGF-1/growth hormone axis is involved in human cancer risk [Maturitas 29 (1998) 61; Horm. Res. 51 (1999) 34; Eur. J. Cancer 36 (2000) 1224; Maturitas 41 (2002) 299] Some progestins also have effects on the enzymes in breast tissue that are responsible for the local synthesis of estradiol. Thus, whilst progestins without androgenic action have been found to markedly inhibit these enzymes, an equivalent degree of inhibition is not achieved with testosterone-derivatives. Therefore, special attention should be paid to the various partial actions of the different progestins and their effects on breast tissue. Furthermore, factors such as the duration of breast tissue exposure to progestin activity, the influence of different regimens on protective apoptotic mechanisms in the breasts, as well as dose levels and the degree of mammary gland tissue differentiation throughout treatment, should also be considered.

Estrogen agonists/antagonists may down-regulate growth hormone signaling in hepatocytes--an explanation for their impact on IGF-I, IGFBP-1, and lipoprotein(a)

Estrogen agonists/antagonists, when administered orally, exert a range of effects on hepatic function, some of which are potentially protective. These effects include reduced synthesis of IGF-I and apolipoprotein(a), and increased synthesis of IGFBP-1--shifts which arguably could decrease risk for vascular disease and certain cancers. These effects are diametrically opposite to those of growth hormone (GH), which boosts hepatic production of IGF-I and apolipoprotein(a), while suppressing that of IGFBP-1. Thus, a parsimonious explanation of these phenomena is that oral estrogen blunts the efficiency of GH signaling in the liver. Oral androgenic progestins may have the reverse effect. It may be of particular value to determine whether certain estrogen agonists/antagonists can exert relatively 'hepatospecific' activity when administered orally--thus enabling down-regulation of systemic IGF-I activity and of lipoprotein(a), without however inducing a significant increase in systemic estrogen activity. Preliminary evidence suggests that flax lignans and perhaps other phytoestrogens may have potential in this regard.

Modification of serum IGF-I, IGFBPs and SHBG levels by different HRT regimens

During the menopause, levels of SHBG, IGF-I and IGFBPs are significantly modified by the use of different HRT regimens.

OBJECTIVE

The aim of this study is to evaluate the influence of three different HRT regimens on serum levels of SHBG, IGF-I, IGFBP-1 and IGFBP-3 in postmenopausal women.

METHODS

41 postmenopausal women requesting HRT were enrolled in the study. Subjects were divided in three groups according to the therapy assigned; Group A: estradiol 2 mg/day+cyproterone acetate 1 mg/day in a cyclic sequential regimen; Group B: estradiol hemihydrate 2 mg/day plus norethisterone acetate (NETA) 1 mg/day in a continuous combined regimen; Group C: estradiol hemihydrate 1 mg/day plus NETA 0.5 mg/day in a continuous combined regimen. Blood samples were drawn before the start of hormonal treatment and after 6 months of HRT. Levels of SHBG, IGF-I, IGFBP-1 and IGFBP-3 in the serum were measured by means of a specific immunoassay.

RESULTS

In group A, a significant increase of SHBG, no change of IGFBPs and a significant decrease of IGF-I were observed; in group B and in group C, no significant variations for any of the parameters were recorded.

CONCLUSIONS

The association of cyproterone acetate to oral estradiol determines a significant reduction of IGF-I levels and an increase of SHBG; nevertheless, it does not seem to influence the serum levels of the IGF-I binding proteins. The treatment with oral continuous combined estrogens plus androgenic progestins, at low doses, produces minor, not significant, changes in the circulating levels of IGF-I, SHBG and IGFBPs.

A low-fat, whole-food vegan diet, as well as other strategies that down-regulate IGF-I activity, may slow the human aging process

A considerable amount of evidence is consistent with the proposition that systemic IGF-I activity acts as pacesetter in the aging process. A reduction in IGF-I activity is the common characteristic of rodents whose maximal lifespan has been increased by a wide range of genetic or dietary measures, including caloric restriction. The lifespans of breeds of dogs and strains of rats tend to be inversely proportional to their mature weight and IGF-I levels. The link between IGF-I and aging appears to be evolutionarily conserved; in worms and flies, lifespan is increased by reduction-of-function mutations in signaling intermediates homologous to those which mediate insulin/IGF-I activity in mammals. The fact that an increase in IGF-I activity plays a key role in the induction of sexual maturity, is consistent with a broader role for-IGF-I in aging regulation. If down-regulation of IGF-I activity could indeed slow aging in humans, a range of practical measures for achieving this may be at hand. These include a low-fat, whole-food, vegan diet, exercise training, soluble fiber, insulin sensitizers, appetite suppressants, and agents such as flax lignans, oral estrogen, or tamoxifen that decrease hepatic synthesis of IGF-I. Many of these measures would also be expected to decrease risk for common age-related diseases. Regimens combining several of these approaches might have a sufficient impact on IGF-I activity to achieve a useful retardation of the aging process. However, in light of the fact that IGF-I promotes endothelial production of nitric oxide and may be of especial importance to cerebrovascular health, additional measures for stroke prevention-most notably salt restriction-may be advisable when attempting to down-regulate IGF-I activity as a pro-longevity strategy.

Pathologic and biological prognostic factors of breast cancers in short- and long-term hormone replacement therapy users

BACKGROUND

Breast cancer tumors occurring in hormone replacement therapy (HRT) users are less aggressive, but no studies have compared tumor aggressiveness among HRT users by length and mode of therapy.

METHODS

A total of 1105 consecutive postmenopausal patients treated for operable breast cancer at the European Institute of Oncology were identified. Women exposed to HRT were compared with HRT nonusers by clinical stage at presentation and pathologic and biological tumor characteristics. HRT duration and administration modality were analyzed in relation to tumor characteristics in the HRT group.

RESULTS

Better stage distribution, including smaller pathologic tumor diameter and fewer involved axillary lymph nodes, was seen in the HRT group. Estrogen receptor-positive tumors were more frequent in the control group, but this tendency was reversed with longer exposure to HRT. Histological grade III tumors were less frequent in the HRT group. More favorable prognostic factors were associated with HRT >5 years. The proliferative fraction was higher in patients with exposure <1 vs. >5 years and in oral versus transdermal users.

CONCLUSIONS

Breast cancers developing during HRT have better prognostic characteristics than those seen in HRT nonusers. A trend toward better prognostic characteristics with increasing duration of HRT was seen.

Breast cancer and hormone replacement therapy: putting the risk into perspective

Data on hormone replacement therapy and breast cancer risk come from a number of observational studies (mostly American studies). Those published up to 1995 were reanalyzed by the Collaborative Group on Hormonal Factors in Breast Cancer (CGHFBC). They involved populations where exceedingly high estrogen doses were used as first-line therapy, and a progestin was added in a minority of women. Overall, the CGHFBC reanalysis found that the relative risk increased by 0.023 for each year of use (with an absolute excess risk of two or six cases out of 1000 women treated for 5 or 10 years, respectively). Further American studies, published in 2000 and involving populations where lower doses were used, showed a risk increase of 0.01 per year of estrogen-only use. Both the CGHFBC reanalysis and the further studies did not find an increase of risk in treated overweight women. Possibly, overweight women already have a maximal estrogenic stimulus on the breast due to extraglandular estrogen production. An additional explanation could be that oral estrogens, through their hepatocellular effects, reverse some biological features of obesity (e.g. decreased sex hormone binding globulin level and increased insulin-like growth factor-I bioactivity) that potentially increase breast cancer risk, so balancing the estrogen stimulation. The CGHFBC reanalysis did not show a substantial difference in breast cancer risk between the majority using estrogen alone and the small minority using estrogen plus progestin. Conversely, Swedish studies and the recent American studies suggest that the risk increase could be higher with the addition of a progestin, compared with estrogen-only use. The biological effect of progesterone/progestins on the breast tissue is controversial. Even if the observed increase in risk could be partially ascribed to non-progesterone-like effects of some progestins (e.g. opposing the hepatocellular effects of oral estrogens) and also (in the American studies) to use-bias, a detrimental action due to progesterone-like effects cannot be excluded. However, the theoretical possibility exists that low doses of oral estrogens, plus a progestin providing progesterone-like effects only, will be shown to be associated with a limited breast cancer risk increase.

Modulation of adipocyte lipoprotein lipase expression as a strategy for preventing or treating visceral obesity

As compared to subcutaneous adipocytes, visceral adipocytes have high basal lipolysis, are highly sensitive to catecholamines, and are poorly sensitive to insulin; these traits are amplified when visceral adipocytes hypertrophy. As a result, enlarged visceral fat stores tend to flood the portal circulation with free fatty acids at metabolically inappropriate times when fatty acids are unlikely to be oxidized, thus exposing tissues to excessive free fatty acid levels and giving rise to the insulin resistance syndrome. A logical approach to preventing or correcting visceral obesity is to down-regulate the lipoprotein lipase (LPL) activity of visceral adipocytes relative to that expressed in subcutaneous adipocytes and skeletal muscle. IGF-I activity appears to be a primary determinant of visceral LPL activity in humans; systemic IGF-I activity is decreased when diurnal insulin secretion is low, when hepatocytes detect a relative paucity of certain essential amino acids, and when estrogens are administered orally. The ability of alpha-glucosidase inhibitor therapy to selectively reduce visceral adiposity suggests that down-regulation of diurnal insulin secretion and/or IGF-I activity may indeed have a greater impact on LPL activity in visceral fat than in subcutaneous fat. Thus, low-glycemic-index, vegan, high-protein, or hypocaloric diets can be expected to decrease visceral LPL activity, as can postmenopausal estrogen therapy. Furthermore, estrogen enhances the LPL activity of non-pathogenic gluteofemoral fat cells, whereas testosterone decreases visceral LPL activity in men; this may explain why sex hormone replacement in middle-aged people of both sexes has a favorable impact on visceral fat and insulin sensitivity. Beta-adrenergic activity suppresses transcription of LPL in adipocytes; this phenomenon may contribute to the favorable impact of exercise training on visceral obesity; conceivably, preadministration of safe drugs that boost catecholamine activity (caffeine, yohimbine) could potentiate this beneficial effect of exercise. Glucocorticoids selectively increase the LPL activity of visceral adipocytes; while there is currently no convincing evidence that psychological stress is a major determinant of visceral adiposity, or that stress management techniques can help to correct visceral obesity, reports that anxiolytic therapy can improve glycemic control in type 2 diabetes should encourage further research along these lines.

Concurrent administration of sustained-release bezafibrate may counteract the increased thrombotic risk associated with oral estrogen therapy

Although hormone replacement therapy (HRT) can have many favorable effects on serum lipids and on vascular endothelium that presumably mediate the decreased risk for heart attack and stroke associated with HRT in observational epidemiology, oral estrogen also has various pro-coagulant effects: increases in serum triglycerides and factor VII activity, decreases in serum antithrombin III and protein S. This may explain the increased risk for venous thromboembolism observed with HRT and oral contraceptives, as well as the temporary increase in coronary risk noted when women with preexisting coronary disease initiate HRT. The well-tolerated hypolipidemic agent bezafibrate has anticoagulant actions that are diametrically opposed to the procoagulant effects of oral estrogen: namely, reductions in serum triglycerides and factor VII activity, and an increase in antithrombin III. However, bezafibrate could be expected to complement the protective effects of oral estrogen on serum lipids and on serum IGF-I activity. Thus, there is reason to believe that concurrent bezafibrate administration would minimize any thrombotic risk associated with HRT or oral contraception, while amplifying the health benefits of oral estrogen, and would make it more feasible to administer these therapies in women at increased vascular risk. These predictions require confirmation in controlled clinical studies. Certain natural hypolipidemic agents may also have potential as adjuvants to oral estrogen, but their effects on hemostasis require further investigation.

Genetic factors related to racial variation in plasma levels of insulin-like growth factor-1: implications for premenopausal breast cancer risk

The oral contraceptive pill is associated with a modest increase in the risk of early-onset breast cancer in the general population, but it is possible that the risk is higher in certain subgroups of women. The relative risk of breast cancer associated with oral contraceptive use has been reported to be higher for African-American women than for white women. African-American women also have a higher incidence of premenopausal breast cancer than white women. Circulating levels of insulin-like growth factor-1 (IGF-I) vary between ethnic groups and are positively associated with the risk of premenopausal breast cancer. In general, the plasma level of IGF-I is lower in women who take oral contraceptives than in women who do not. In an attempt to explain the observed ethnic difference in IGF-I levels with oral contraceptive use, we sought to identify polymorphic variants of genes that are associated with IGF-I levels and estrogen metabolism. We measured IGF-I and IGFBP-3 plasma levels in 503 nulligravid women between the ages of 17 and 35. All women filled out a questionnaire that included information about ethnic background and oral contraceptive use. Samples of DNA were used to genotype the women for known polymorphic variants in the IGF1, AIB1, and CYP3A4 genes. Black women had significantly higher mean IGF-I levels than white women (330 ng/ml versus 284 ng/ml; P = 0.001, adjusted for age and oral contraceptive use). IGF-I levels were significantly suppressed by oral contraceptives in white women (301 ng/ml versus 267 ng/ml; P = 0.0003), but not in black women. Among oral contraceptive users, the IGF-I level was positively associated with the absence of the IGF1 19-repeat allele (338 ng/ml versus 265 ng/ml; P = 0.00007), with the presence of the CYP3A4 variant allele (320 ng/ml versus 269 ng/ml; P = 0.01), and with the presence of the AIB1 26-repeat allele (291 ng/ml versus 271; P = 0.08). After adjusting for genotypes, ethnic group was no longer a significant predictor of the IGF-I level. IGF-I levels are higher among black than white women. Polymorphic variants in the CYP3A4, IGF1, and AIB1 genes are associated with increases in the plasma levels of IGF-I among oral contraceptive users and the variant alleles are much more common in black women than in white women. The high incidence of premenopausal breast cancer among black women may be mediated through genetic modifiers of circulating levels of IGF-I.

Androgenic progestins amplify the breast cancer risk associated with hormone replacement therapy by boosting IGF-I activity

Recent epidemiology indicates that unopposed oral estrogen replacement therapy has a surprisingly small impact on breast cancer risk--little if any in overweight women--whereas combined regimens featuring synthetic progestins are attended by a much larger increase in this risk. These findings may reflect the fact that oral estrogen acts on the liver to down-regulate systemic IGF-I activity, whereas concurrent administration of androgens--including the androgenic progestins often used in replacement therapy--abrogates this effect. Increased systemic IGF-I activity has been linked to increased breast cancer risk, and may be largely responsible for the greater incidence of breast cancer in overweight postmenopausal women--who thus should have the most to gain from suppression of IGF-I activity by oral estrogen. Down-regulation of IGF-I may likewise account for the marked reduction in colon cancer risk associated with current estrogen replacement therapy. Fortunately, natural progesterone--now available in micronized oral preparations--does not oppose the hepatic effects of oral estrogen, and moreover may be preferable to androgenic progestins with respect to vascular function. Oral replacement therapy featuring micronized progesterone, if administered throughout postmenopausal life, can be expected to have a highly positive impact on vascular health, bone density, and risks for Alzheimer's disease and colon cancer--benefits which, in most women, may vastly outweigh the associated increase in risk for breast and endometrial cancers.

Suppression of dolichol synthesis with isoprenoids and statins may potentiate the cancer-retardant efficacy of IGF-I down-regulation

Agents that inhibit the synthesis of mevalonate or of downstream isoprenoids block the G1-S transition and induce apoptosis in many cell lines; these agents include statins, phenylacetate, and a range of cyclic and acyclic isoprenoids. This cytostatic effect is mediated primarily by decreased availability of dolichol; this deficit impedes the glycosylation of nascent IGF-I receptors, preventing their transfer to the cell surface. In most tissues as well as transformed cell lines, IGF-I activity is crucial for transition to S phase, and also prevents apoptosis. Thus, down-regulation of serum levels of free IGF-I - as may be achieved by caloric restriction, low-fat vegan diets, and various estrogen agonists/antagonists - may represent a useful strategy for preventing and controlling cancer; however, a compensatory up-regulation of tissue expression of IGF-I receptors limits the efficacy of such an approach. Concurrent use of agents that inhibit dolichol synthesis can be expected to prevent an increase in plasma membrane IGF-I receptors, thus potentiating the cancer-retardant efficacy of IGF-I down-regulation. Since dolichol and IGF-I appear to be essential for angiogenesis, these measures may also prove useful for control of pathogenic neovascularization.

Hormone replacement therapy and breast cancer

There is considerable evidence that the risk of breast cancer is related to ovarian function. However, the effect of postmenopausal hormone replacement therapy (HRT) on breast cancer risk continues to be debated in the absence of data from randomised controlled trials. Observational studies suggest that HRT probably promotes the growth of pre-existing breast cancers rather than initiating malignant transformation of breast epithelial cells but without exerting an obviously detrimental effect on disease-specific mortality. The controversy surrounding HRT and breast cancer has become additionally more complex as a result of the dilemma faced by clinicians advising women rendered oestrogen-deficient by breast cancer therapy. Whilst HRT is currently contra-indicated due to theoretical concerns that it will promote disease recurrence, its increasing, ad hoc prescription to symptomatic breast cancer patients has not been associated with an increase in disease recurrence. Large-scale randomised trials of HRT in healthy women and breast cancer survivors are now ongoing but it will be some years before useful clinical information becomes available. Until then, the limitations and biases implicit as a result of the design of observational studies must be borne in mind when interpreting such studies.

HRT and breast cancer risk: a clue for interpreting the available data

Epidemiological and biological data on HRT and breast cancer risk are reviewed. Some aspects deserve consideration. (1) The majority of epidemiological data have been gathered from populations where high estrogen doses (> or = 1.25 mg daily of conjugated estrogens) were used as first line therapy. (2) HRT does not increase the risk in overweight women, even in the series in which a risk increase (in longterm users) is found. This could be as a result of the fact that oral estrogens, through their metabolic and hepatocellular effects, reverse some biological features of obesity (e.g. increased insulin-like growth factor I activity and decreased sex hormone binding globulin level) which potentially increase breast cancer risk, so balancing the estrogen stimulation. (3) The progestin addition seems to increase the risk when the 19 nor-testosterone derivatives are used. These androgenic compounds contrast the metabolic and hepatocellular effects of oral estrogens. To sum up, the possibility does exist that even the longterm use of oral estrogens at the right ('low') dose, with the addition of a non-androgenic progestin, will be shown to be associated with a very limited breast cancer risk increase.

HRT, breast and endometrial cancers: strategies and intervention options

The demand for hormone replacement therapy (HRT) by women who enter the menopause is rapidly increasing in all developed countries. The concern that HRT may enhance morbidity and mortality from malignant diseases still limits the widespread adoption of hormonal treatments. Overall, epidemiological data on cancer incidence and HRT are reassuring, although long-term or inappropriate therapies may slightly increase the risk of developing malignant diseases. Many commercial hormonal compounds are currently available and the safest HRT regimen with regard to cancer risk must be identified. It is equally important that the best strategies for breast and endometrial surveillance in women commencing HRT be outlined, bearing in mind that the diffusion of hormonal therapies may be halted by unnecessary medical interventions.

Insulin-like growth factor I (IGF-I) serum level modifications during transdermal estradiol treatment in postmenopausal women: a possible bimodal effect depending on basal IGF-I values

The objective of this study was to determine the influence of transdermal estradiol administration on insulin-like growth factor I (IGF-I) serum level in a series larger than those published to date. Thirty-nine postmenopausal women with vasomotor symptoms were studied; blood samples (after overnight fast) were obtained just before and at the 6th month of treatment with transdermal estradiol 0.05 mg/day, and serum levels of IGF-I, growth hormone and sex hormone binding globulin (SHBG) were evaluated. Sixteen of the 39 women did not show variations of IGF-I values (group A), while 11 showed an increase (group B) and 12 showed a decrease (group C) by at least 20% with transdermal estradiol treatment. IGF-I basal levels were higher in group C as compared to group A (p < 0.05) and to group B (p < 0.01), intermediate in group A, and lower in group B. Group C showed a significant increase of SHBG values with transdermal estradiol treatment. Transdermal estradiol seems to induce a bimodal effect on IGF-I serum levels, depending on IGF-I basal values. This could be caused by a different responsivity to estrogen action on the liver (the major site of circulating IGF-I production) and also, possibly, by a different degree in insulin sensitivity changes caused by estrogen.