Estrogen use and breast cancer. Interaction with body mass

Variability of breast cancer risk in observational studies of hormone replacement therapy: a meta-regression analysis

OBJECTIVES

A re-analysis of data from 51 epidemiological studies reported a significant 14% increase in the risk of breast cancer associated with the use of hormone replacement therapy (HRT). Unlike randomized trials, these observational studies varied in design and methods. This study was conducted to explore the impact of study design factors on the rate ratio.

METHODS

We performed a meta-regression analysis of 39 epidemiological studies of HRT and breast cancer. The rate ratio of breast cancer associated with ever use of HRT was evaluated in relation to study design, study period, country, primary study objective, method of exposure measurement, age control, adjustment factors related to reproduction and menopause, and the presence of breast cancer surveillance. We used stepwise multiple regression analysis, weighted by the inverse of the variance of the logarithm of the rate ratio, to estimate ratios of rate ratios for these factors.

RESULTS

Exposure measured by personal interview and/or medical record review was associated with a 14% lower rate ratio estimate as compared with telephone interview or self-administered questionnaire (P = 0.018). Among studies that did not adjust for age at menopause, the rate ratio was 12% lower if the primary objective was HRT effect than not (P = 0.016), while it was 43% higher among studies that adjusted for age at menopause (P = 0.042). An index that included as six desirable design features, breast cancer surveillance, matching of controls, more reliable exposure information, adjustment for age at menopause and reproductive risk factors, and as primary objective the effect of HRT suggests that studies with none of these properties would lead to a rate ratio estimate of 1.14 (95% CI: 1.00-1.29) while studies with all six properties would produce a rate ratio of 0.98 (95% CI: 0.83-1.15).

CONCLUSIONS

Design factors of epidemiological studies could be an alternative explanation for the reported 14% increase in the risk of breast cancer associated with the use of HRT.

Postmenopausal estrogen use and invasive versus in situ breast cancer risk

To examine the effect of cancer histopathology on the relationship between estrogen-replacement therapy (ERT) use and breast cancer risk, we performed a case-control study of 109 postmenopausal women 45 years or older with in situ or invasive breast cancer matched to 545 controls. When in situ and invasive tumors were combined, the overall odds ratio (OR) describing the association between ERT use and breast cancer risk was not statistically significantly elevated (adjusted OR = 1.48, 95% confidence interval [CI] = 0.89-2.47). When the analyses were confined to women with invasive disease, risk estimates were uniformly higher (adjusted OR = 1.85, 95% CI = 1.00-3.45). In contrast, the overall estimate for the relationship between ERT use and in situ breast cancer was close to 1 (adjusted OR = 1.08, 95% CI = 0.42-2.77). The positive association between ERT use and invasive breast cancer we observed, and the lack of association in women with in situ disease, may represent a distinct biological difference or may be related to the small sample size of our study.

Breast cancer and hormone replacement therapy: collaborative reanalysis of data from 51 epidemiological studies of 52,705 women with breast cancer and 108,411 women without breast cancer. Collaborative Group on Hormonal Factors in Breast Cancer

BACKGROUND

The Collaborative Group on Hormonal Factors in Breast Cancer has brought together and reanalysed about 90% of the worldwide epidemiological evidence on the relation between risk of breast cancer and use of hormone replacement therapy (HRT).

METHODS

Individual data on 52,705 women with breast cancer and 108,411 women without breast cancer from 51 studies in 21 countries were collected, checked, and analysed centrally. The main analyses are based on 53,865 postmenopausal women with a known age at menopause, of whom 17,830 (33%) had used HRT at some time. The median age at first use was 48 years, and 34% of ever-users had used HRT for 5 years or longer. Estimates of the relative risk of breast cancer associated with the use of HRT were obtained after stratification of all analyses by study, age at diagnosis, time since menopause, body-mass index, parity, and the age a woman was when her first child was born.

FINDINGS

Among current users of HRT or those who ceased use 1-4 years previously, the relative risk of having breast cancer diagnosed increased by a factor of 1.023 (95% CI 1.011-1.036; 2p=0.0002) for each year of use; the relative risk was 1.35 (1.21-1.49; 2p=0.00001) for women who had used HRT for 5 years or longer (average duration of use in this group 11 years). This increase is comparable with the effect on breast cancer of delaying menopause, since among never-users of HRT the relative risk of breast cancer increases by a factor of 1.028 (95% CI 1.021-1.034) for each year older at menopause. 5 or more years after cessation of HRT use, there was no significant excess of breast cancer overall or in relation to duration of use. These main findings did not vary between individual studies. Of the many factors examined that might affect the relation between breast cancer risk and use of HRT, only a woman's weight and body-mass index had a material effect: the increase in the relative risk of breast cancer associated with long durations of use in current and recent users was greater for women of lower than of higher weight or body-mass index. There was no marked variation in the results according to hormonal type or dose but little information was available about long durations of use of any specific preparation. Cancers diagnosed in women who had ever used HRT tended to be less advanced clinically than those diagnosed in never-users. In North America and Europe the cumulative incidence of breast cancer between the ages of 50 and 70 in never-users of HRT is about 45 per 1000 women. The cumulative excess numbers of breast cancers diagnosed between these ages per 1000 women who began use of HRT at age 50 and used it for 5, 10, and 15 years, respectively, are estimated to be 2 (95% CI 1-3), 6 (3-9), and 12 (5-20). Whether HRT affects mortality from breast cancer is not known.

INTERPRETATION

The risk of having breast cancer diagnosed is increased in women using HRT and increases with increasing duration of use. This effect is reduced after cessation of use of HRT and has largely, if not wholly, disappeared after about 5 years. These findings should be considered in the context of the benefits and other risks associated with the use of HRT.

Hormone replacement therapy and risk for breast cancer

Because breast cancer will develop in one of every nine American women, even a small increase in risk associated with a widespread exposure is of substantial public health concern. Although most studies have not found ever use of estrogens to be a risk factor for breast cancer, it is not yet resolved whether current or long-term users experience some increase in risk. Given the fact that the indications for menopausal estrogen use have changed substantially over time, from short-term use for the relief of menopausal symptoms to long-term use for lifetime reduction of conditions such as cardiovascular disease and osteoporosis, it is imperative that the effects of long-term estrogen replacement on the risk for breast cancer be resolved. These studies are not without associated methodologic difficulties, with the ultimate interpretation of the association possibly dependent on the results of controlled clinical trials. Although such investigations are currently underway, the results will not be available for many years. To address more immediate concerns, continued emphasis should be placed on well-designed case-control and cohort studies. For the results to be reliable, attention must be directed to the effects of selection, recall and surveillance biases, confounding factors, detailed exposure relationships, subgroup variations, and disease associations. In addition, given the increasing trend for estrogens to be prescribed in combination with progestogens, the effects on breast tissue of this combined therapy merit immediate attention.

Does hormone replacement therapy increase the risk of breast cancer?

The data contained in the literature about breast cancer risk and hormone replacement therapy is reviewed. Many studies with different methodologies have been published. Analysis of classical papers or of meta-analysis do not support the view that short-term use of hormone replacement therapy significantly increases the risk of breast cancer. In some clinical situations such as family history of breast cancer, high dose estrogens and especially in the case of long term treatment over 10 years, risk of cancer could be increased and requires a specific clinical management. Despite of the absence of double blind placebo-controlled trial, there is no strong data available to oppose the use of estrogen replacement therapy because of an hypothetic increased risk of breast cancer. Using a low posology for less than 5 years in correctly managed women is a safe attitude.

Biological and endocrinological insights into the possible breast cancer risk from menopausal estrogen replacement therapy

The question of whether estrogen therapy increases the risk of breast cancer is reviewed. Despite more than 60 epidemiological studies and several meta-analyses over a five-decade period, there is no consensus about the answer. At present, the majority of investigators agree that short-term or medium-term therapy (less than 10 years) poses no measurable risk; some, but not all, investigators feel that there is a modest risk with long-term therapy (more than 15 years). Even this semi-consensus is clouded by the startling and clear-cut finding of the largest ever epidemiological study, the Nurses Surveillance Study, that a small increase in risk with estrogen therapy occurred only in women who also ingested alcohol, itself a known risk factor for breast cancer; women who did not ingest alcohol were at no increased risk. Because virtually none of the other epidemiological studies has controlled for alcohol ingestion, the conclusions of all of them are placed in doubt. To try to shed light on this problem, the 60-year-old studies of Lacassagne et al. on the induction of breast cancer in mice by estrogens were reviewed. They found that the magnitude and timing of the inducing effect of estrogen depended on the spontaneous breast cancer incidence in the mouse strain studied: in no-incidence strains, no cancer was induced; in high-incidence strains, induction was rapid and universal; in low-incidence strains, only a low percentage of animals had cancer induced, and it required prolonged estrogen administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimate of breast cancer risk reduction with weight loss

Upper body fat localization has been associated with an increased risk of cancer. This study demonstrated that 64.2% of 124 women with at least a 4.5-kg weight loss decreased their upper body fat localization, as measured by a reduction in their suprailiac-thigh skin fold ratio and other skin fold thicknesses associated with upper body fat localization. Based on a risk model previously developed for breast cancer and upper body fat localization, a reduction in estimated breast cancer relative risk of 45% was calculated for the entire group of women who lost 4.5 kg or more in weight. Greater weight loss further reduced upper body fat localization and estimated breast cancer risk based on this model.

Obesity, body fat distribution, and sex hormones in breast cancer patients

This study addresses the relationship between female sex hormones, obesity, body fat distribution, and breast cancer. Increasing obesity correlated with a progressive fall in sex hormone-binding globulin (SHBG) level and an increase in testosterone level. Premenopausal breast cancer patients were found to have significantly lower levels of SHBG compared with age-matched and weight-matched controls. This difference in SHBG level was not noted in postmenopausal breast cancer patients. The SHBG level decreased with increasing upper body fat localization in breast cancer patients and controls. This effect was more marked in breast cancer patients which may explain our earlier finding that women with upper body fat localization are at increased risk for developing breast cancer.

Obesity and body fat distribution and breast cancer prognosis

This study addresses the effect of obesity and body fat distribution on axillary lymph node involvement, tumor size, and estrogen receptor (ER) level in breast cancer patients. Anthropometric measurements were prospectively obtained on 248 consecutively and newly diagnosed women with invasive breast cancer. The anthropometric measurements evaluated were abdomen, thigh, subscapular, and midaxillary skinfolds; weight; and height. Weight and Quetelet Index (kg/m2) were significantly (P = 0.001) associated with lymph node involvement in postmenopausal patients. The abdomen:thigh skinfold ratio was significantly higher in premenopausal patients (P = 0.004) and postmenopausal (P = 0.03) without axillary node involvement compared with women with 4+ axillary node involvement. The abdomen:thigh skinfold was higher (P = 0.05) in women with smaller breast cancers (less than 2.0 cm) and higher ER levels. Weight and Quetelet Index did not affect tumor size or ER level. This study demonstrated that obese postmenopausal women who developed breast cancer tend to have more axillary node involvement than their leaner counterparts. Generalized obesity did not affect tumor size or ER level. Premenopausal and postmenopausal women with upper body fat distribution appear to be a subset of women who have a more favorable prognosis as measured by less lymph node involvement, smaller tumors, and higher levels of ER in their tumors.

What can a woman do about her risk of dying of breast cancer?

Every day, American women are told that one in ten will develop breast cancer, and some groups perceive their risk to be so high as to justify immediate bilateral mastectomy. Many associations with breast cancer have been identified, including a history of benign breast diseases, in situ carcinoma, a family history of breast cancer, prolonged menstruation as a result of early menarche or delayed menopause, few or late pregnancies, excessive alcohol intake, obesity, and possibly the use of estrogens as oral contraceptives or postmenopausal replacement therapy. In spite of these associations, our understanding of either the cause(s) of breast cancer or the sequence of events leading to a diagnosis of breast cancer is still inadequate to make global public health recommendations regarding life style--or even to initiate well-designed studies. The epidemiologic evidence strongly suggests, however, that events relatively early in a woman's life are more important than later events, even though most of the risk of developing breast cancer will be expressed after the age of 75. Possibly one of the greatest contributions we can make to our patients' welfare is to share the knowledge that the risk of dying of breast cancer is considerably smaller than the risk of developing breast cancer; that the risk of early death from breast cancer rarely exceeds 10% in even the highest risk groups; and that the life styles most likely to reduce the risk of cardiovascular disease and other scourges of womankind are also those most likely to reduce the risk of developing breast cancer.

The role of exogenous hormones in the epidemiology of breast, ovarian and endometrial cancer

This review focuses on the effects of oral contraceptives (OC) and estrogen replacement therapy (ERT) on the risk of breast, ovarian and endometrial cancer. The relationship between OC and cancer risk is first placed in a historical perspective. Since 1960, when OC were introduced, the hormonal composition of OC as well as the characteristics of the OC user have changed considerably. Studies conducted in the 1970s were generally reassuring, but it was not until the 1980s that studies could evaluate the effect of prolonged OC use after an extended follow-up period. Although the relationship between breast cancer and OC has been investigated in about 40 studies, the issue still remains essentially unresolved. Most studies report no association between ever use of OC and breast cancer risk. Several studies find increased risk for prolonged use and other studies report elevated risks for women who used OC very early in their reproductive years. The inconsistent results of recent studies are attributed to bias or to geographical variation in latency period elapsed, types of OC preparations, or prevalence of other risk factors. In contrast, the use of combined OC has consistently been shown to reduce the risk of ovarian and endometrial cancer. The risk further decreases with increasing duration of use and the protective effect seems to persist in ex-users for at least 5 years. Some evidence indicates that higher parity reduces the protective effect. Though studies relating ERT to breast cancer are far from consistent, overall, there is evidence for a moderately increased risk with high dose and/or long duration. The effect seems to be modified by mode of administration (injections vs. pills) and by type of ERT, but this needs confirmation. The number of adequate studies on the relationship between ERT and ovarian cancer is too small to draw firm conclusions. The positive relationship between ERT and endometrial cancer is now well established. The ERT effect is dose- and duration-dependent and is characterized by a short latency period. The cyclic addition of progesterone (greater than 10 days/cycle) may reduce the risk increase.

The cancer question: an overview of recent epidemiologic and retrospective data

Unopposed estrogen stimulates mitotic activity in endometrial and breast tissue. Numerous case-control studies have evaluated the relationship between estrogen use and the risk of endometrial and breast cancers. In general, exogenous, unopposed estrogen use increases the risk of endometrial cancer by tenfold and of breast cancer by twofold after long-term use of high doses. Estrogen's positive effects on osteoporosis and coronary heart disease must be considered when evaluating the potential risks associated with its use in postmenopausal women.

Cardiovascular benefits of estrogen replacement therapy

Epidemiologic case-study and cohort-study data concerning effects of estrogen replacement therapy on the risk of cardiovascular disease in postmenopausal women are reviewed. Although there is conflicting literature, most research strongly suggests that estrogens, and estrogen replacement therapy in particular, reduce the risk of cardiovascular disease. Such reduced risk in estrogen users is most likely mediated in part by the beneficial effects of estrogen therapy on lipid metabolism. Risks associated with the use of estrogens and possible effects when progestational agents are added to an estrogen regimen are also discussed.

Non-contraceptive exogenous oestrogen therapy and breast cancer

Previous evidence of an increased risk of breast cancer in association with the use of non-contraceptive exogenous oestrogen therapy has not been consistent. In this population-based case-control study of breast cancer (comprising 451 case-control pairs in all) the relationship between the use of non-contraceptive exogenous oestrogen therapy and the risk of breast cancer was examined in the 281 case subjects and 288 control subjects (262 case-control pairs) who were postmenopausal, since the major reported indication for the use of exogenous oestrogen therapy is for the relief of menopausal symptoms. "Ever use" of exogenous oestrogen therapy was associated with an adjusted relative risk of 1.03 (95% confidence interval, 0.62-1.69). The risk of breast cancer was not associated with the duration of use, years since first use, or years since last use of exogenous oestrogen therapy. Stratified analyses of breast cancer showed a 35% increase in risk in nulliparous women that is associated with the use of exogenous oestrogen therapy, a 40% reduction in risk in women with a history of benign breast disease (both statistically not significant), and a statistically significant 70% reduction in risk in women with a history of bilateral oophorectomy. The results of this study should be weighed against those of several earlier studies which suggest caution in the prescription of replacement oestrogen therapy for those women who are known already to be at an increased risk of breast cancer.

Hormone replacement therapy and breast cancer

Numerous studies on oestrogen replacement therapy have failed to incriminate the use of exogenous oestrogen as a cause of breast cancer in post-menopausal women. Since so many variables influence breast cancer risk, it has not been possible for any single study to evaluate every potential risk factor included in the epidemiological and clinical reports on hormone use and carcinoma of the breast. The relative risk (RR) for breast cancer in oestrogen users has been found to vary from 0.4 to 3.4, with the vast majority of investigators reporting an RR very close to 1.0, or no increased risk at all. There is growing evidence that progesterone deficiency may increase the risk for breast cancer in some women. At least three studies have indicated that the addition of progestogen to oestrogen replacement therapy may significantly decrease the risk for carcinoma of the breast. It was observed that the RR of breast cancer varied from 0.47 to 0.89 in these studies when oestrogen-progestogen users were compared with unopposed oestrogen users. However, it is pointed out that progestogens are not added to oestrogen replacement therapy to negate an increased risk of breast cancer from unopposed oestrogens, since oestrogen therapy does not increase the risk. Combination oestrogen-progestogen therapy is recommended for hormone replacement treatment, even in women who have had a hysterectomy, because it will reduce the risk for breast cancer in some women.

Menopausal oestrogens and breast cancer risk: an expanded case-control study

A study among 1960 post-menopausal breast cancer cases and 2258 controls identified through a nation-wide screening program enabled evaluation of effects of oestrogen use on breast cancer risk. Ever use was not associated with increased risk (RR = 1.0), but a significant trend was observed with increasing years of use, with users of 20 or more years being at a 50% excess risk. Elevations associated with long-term use were apparent across all menopause subgroups (natural, ovaries retained, ovaries removed). Hormones exerted particularly adverse effects in those initiating use subsequent to a diagnosis of benign breast disease, particularly long-term users (RR = 3.0, 95% CI 1.6-5.5). There was also some indication that effects predominated among the lower stage tumours, an observation similar to that observed for endometrial cancer. These findings support a role for oestrogens in the aetiology of breast cancer, although risk appears to be enhanced only after extended periods of use, and not to the extent observed for other hormonally-sensitive tumours.

Proposal to decrease the risk and improve the prognosis of breast cancer

Of 256 patients with breast cancer diagnosed between 1972 and 1981, 102 have died (mortality, 39.8%). More hormone users had negative axillary nodes (57.1%) than did nonusers (41.8%). The mortality of the hormone users (22.2%) was significantly lower (p less than or equal to 0.01) than that of the nonusers (45.5%). In 162 patients whose diagnosis of breast cancer was made prior to 1979, the 5-year survival rate in hormone users was 76.2% compared to 48.1% in nonusers. During the prospective phase of the study from 1975 to 1981, the lowest incidence of breast carcinoma (67.3:100,000) was observed in the estrogen-progestogen users and was significantly lower than that of the untreated group (342.3:100,000) and lower than that expected from both the Third National Cancer Survey and the National Cancer Institute System for Electronic Evaluation and Retrieval (SEER) data (p less than or equal to 0.01). Estrogen therapy does not increase the risk of mammary malignancy, but added progestogen significantly decreases the risk.