Relationship between risk factors for breast cancer and hormonal status

Modern reproductive patterns associated with estrogen receptor positive but not negative breast cancer susceptibility

It has long been accepted that modern reproductive patterns are likely contributors to breast cancer susceptibility because of their influence on hormones such as estrogen and the importance of these hormones in breast cancer. We conducted a meta-analysis to assess whether this ‘evolutionary mismatch hypothesis’ can explain susceptibility to both estrogen receptor positive (ER-positive) and estrogen receptor negative (ER-negative) cancer. Our meta-analysis includes a total of 33 studies and examines parity, age of first birth and age of menarche broken down by estrogen receptor status. We found that modern reproductive patterns are more closely linked to ER-positive than ER-negative breast cancer. Thus, the evolutionary mismatch hypothesis for breast cancer can account for ER-positive breast cancer susceptibility but not ER-negative breast cancer.

Body mass index and breast cancer risk according to postmenopausal estrogen-progestin use and hormone receptor status

To assess the joint relationships among body mass index, menopausal status, and breast cancer according to breast cancer subtype and estrogen-progestin medication use, we conducted a meta-analysis of 89 epidemiologic reports published in English during 1980-2012 identified through a systematic search of bibliographic databases. Pooled analysis yielded a summary risk ratio of 0.78 (95% confidence interval (CI): 0.67, 0.92) for hormone receptor-positive premenopausal breast cancer associated with obesity (body mass index (weight (kg)/height (m)(2)) ≥30 compared with <25). Obesity was associated with a summary risk ratio of 1.39 (95% CI: 1.14, 1.70) for receptor-positive postmenopausal breast cancer. For receptor-negative breast cancer, the summary risk ratios of 1.06 (95% CI: 0.70, 1.60) and 0.98 (95% CI: 0.78, 1.22) associated with obesity were null for both premenopausal and postmenopausal women, respectively. Elevated postmenopausal breast cancer risk ratios associated with obesity were limited to women who never took estrogen-progestin therapy, with risk ratios of 1.42 (95% CI: 1.30, 1.55) among never users and 1.18 (95% CI: 0.98, 1.42) among users; too few studies were available to examine this relationship according to receptor subtype. Future research is needed to confirm whether obesity is unrelated to receptor-negative breast cancer in populations of postmenopausal women with low prevalence of hormone medication use.

Risk factors according to estrogen receptor status of breast cancer patients in Trivandrum, South India

Estrogen receptor (ER) status is an important biomarker in defining subtypes of breast cancer differing in antihormonal therapy response, risk factors and prognosis. However, little is known about association of ER status with various risk factors in the developing world. Our case-control study done in Kerala, India looked at the associations of ER status and risk factors of breast cancer. From 2002 to 2005, 1,208 cases and controls were selected at the Regional Cancer Center (RCC), Trivandrum, Kerala, India. Information was collected using a standardized questionnaire, and 3-way analyses compared ER+/ER- cases, ER+ cases/controls and ER- cases/controls using unconditional logistic regression to calculate odds ratios and 95% confidence intervals. The proportion of ER- cases was higher (64.1%) than ER+ cases. Muslim women were more likely to have ER- breast cancer compared to Hindus (OR = 1.48, 95% CI = 1.09, 2.02), an effect limited to premenopausal group (OR = 1.87, 95% CI = 1.26, 2.77). Women with higher socioeconomic status were more likely to have ER+ breast cancer (OR = 1.48, 95% CI = 1.11, 1.98). Increasing BMI increased likelihood of ER- breast cancer in premenopausal women (p for trend < 0.001). Increasing age of marriage was positively associated with both ER+ and ER- breast cancer. Increased breastfeeding and physical activity were in general protective for both ER+ and ER- breast cancer. The findings of our study are significant in further understanding the relationship of ER status and risk factors of breast cancer in the context of the Indian subcontinent.

Energy balance, physical activity, and cancer risk

This chapter posits that cancer is a complex and multifactorial process as demonstrated by the expression and production of key endocrine and steroid hormones that intermesh with lifestyle factors (physical activity, body size, and diet) in combination to heighten cancer risk. Excess weight has been associated with increased mortality from all cancers combined and for cancers of several specific sites. The prevalence of obesity has reached epidemic levels in many parts of the world; more than 1 billion adults are overweight with a body mass index (BMI) exceeding 25. Overweight and obesity are clinically defined indicators of a disease process characterized by the accumulation of body fat due to an excess of energy intake (nutritional intake) relative to energy expenditure (physical activity). When energy intake exceeds energy expenditure over a prolonged period of time, the result is a positive energy balance (PEB), which leads to the development of obesity. This physical state is ideal for intervention and can be modulated by changes in energy intake, expenditure, or both. Nutritional intake is a modifiable factor in the energy balance-cancer linkage primarily tested by caloric restriction studies in animals and the effect of energy availability. Restriction of calories by 10 to 40% has been shown to decrease cell proliferation, increasing apoptosis through anti-angiogenic processes. The potent anticancer effect of caloric restriction is clear, but caloric restriction alone is not generally considered to be a feasible strategy for cancer prevention in humans. Identification and development of preventive strategies that "mimic" the anticancer effects of low energy intake are desirable. The independent effect of energy intake on cancer risk has been difficult to estimate because body size and physical activity are strong determinants of total energy expenditure. The mechanisms that account for the inhibitory effects of physical activity on the carcinogenic process are reduction in fat stores, activity related changes in sex-hormone levels, altered immune function, effects in insulin and insulin-like growth factors, reduced free radical generation, and direct effect on the tumor. Epidemiologic evidence posits that the cascade of actions linking overweight and obesity to carcinogenesis are triggered by the endocrine and metabolic system. Perturbations to these systems result in the alterations in the levels of bioavailable growth factors, steroid hormones, and inflammatory markers. Elevated serum concentrations of insulin lead to a state of hyperinsulinemia. This physiological state causes a reduction in insulin-like growth factor-binding proteins and promotes the synthesis and biological activity of insulin-like growth factor (IGF)-I, which regulates cellular growth in response to available energy and nutrients from diet and body reserves. In vitro studies have clearly established that both insulin and IGF-I act as growth factors that promote cell proliferation and inhibit apoptosis. Insulin also affects on the synthesis and biological availability of the male and female sex steroids, including androgens, progesterone, and estrogens. Experimental and clinical evidence also indicates a central role of estrogens and progesterone in regulating cellular differentiation, proliferation, and apoptosis induction. Hyperinsulinemia is also associated with alterations in molecular systems such as endogenous hormones and adipokines that regulate inflammatory responses. Obesity-related dysregulation of adipokines has the ability to contribute to tumorigenesis and tumor invasion via metastatic potential. Given the substantial level of weight gain in industrialized countries in the last two decades, there is great interest in understanding all of the mechanisms by which obesity contributes to the carcinogenic process. Continued focus must be directed to understanding the various relationships between specific nutrients and dietary components and cancer cause and prevention. A reductionist approach is not sufficient for the basic biological mechanisms underlying the effect of diet and physical activity on cancer. The joint association between energy balance and cancer risk are hypothesized to share the same underlying mechanisms, the amplification of chemical mediators that modulate cancer risk depending on the responsiveness to those hormones to the target tissue of interest. Disentangling the connection between obesity, the insulin-IGF axis, endogenous hormones, inflammatory markers, and their molecular interaction is vital.

Body weight and incidence of breast cancer defined by estrogen and progesterone receptor status--a meta-analysis

Epidemiological evidence indicates that the association between body weight and breast cancer risk may differ across menopausal status as well as the estrogen receptor (ER) and progesterone receptor (PR) tumor status. To date, no meta-analysis has been conducted to assess the association between body weight and ER/PR defined breast cancer risk, taking into account menopausal status and study design. We searched MEDLINE for relevant studies published from January 1, 1970 through December 31, 2007. Summarized risk estimates with 95% confidence intervals (CIs) were calculated using a random-effects model. The summarized results of 9 cohorts and 22 case-control studies comparing the highest versus the reference categories of relative body weight showed that the risk for ER+PR+ tumors was 20% lower (95% CI=-30% to -8%) among premenopausal (2,643 cases) and 82% higher (95% CI=55-114%) among postmenopausal (5,469 cases) women. The dose-response meta-analysis of ER+PR+ tumors showed that each 5-unit increase in body mass index (BMI, kg/m2) was associated with a 33% increased risk among postmenopausal women (95% CI=20-48%) and 10% decreased risk among premenopausal women (95% CI=-18% to -1%). No associations were observed for ER-PR- or ER+PR- tumors. For discordant tumors ER+PR- (pre) and ER-PR+ (pre/post) the number of cases were too small (<200) to interpret results. The relation between body weight and breast cancer risk is critically dependent on the tumor's ER/PR status and the woman's menopausal status. Body weight control is the effective strategy for preventing ER+PR+ tumors after menopause.

Relation of serum levels of estrogen and dehydroepiandrosterone sulfate to hormone receptor status among postmenopausal women with breast cancer

BACKGROUND

It is hypothesized that breast cancer may consist of heterogeneous diseases with different hormonal environments classified by hormone receptor status. Epidemiologic studies evaluating risk factors for breast cancer by hormone receptor status have supported the hypothesis. However, there are inconsistencies in the risk factor profiles by estrogen receptor (ER) and progesterone receptor (PR) across the studies. To clarify the heterogeneity of the disease, it is necessary to understand not only risk factor profiles but also the biologic characteristics such as the relationships among endogenous sex hormone levels and hormone receptors.

METHODS

We measured serum levels of estrone (E1), estradiol (E2), dehydroepiandrosterone sulfate (DHEAS), and sex hormone-binding globulin (SHBG) in 142 postmenopausal women aged 50 and over with primary breast cancer who had undergone surgical treatment, and investigated the heterogeneity in the relations of endogenous sex hormone levels to hormone receptor status, using the case-series study method. Subjects were categorized into 3 classes based on tertiles of each hormone level in receptor-negative subjects, and odds ratios (ORs) for receptor-positive status compared with receptor-negative status were computed, taking the lowest category as a reference category.

RESULTS

There were clear trends toward higher serum levels of E1, E2, and DHEAS in women with PR+ cancer. The case-series approach revealed that PR+ status might be strongly associated with serum sex hormone levels. In particular, the OR of PR+ was large for a high DHEAS level (OR for the highest category=4.28). No significant association between serum hormone levels and ER status was observed.

CONCLUSION

The association of serum sex hormone levels with hormone receptor status may differ by PR status, but not by ER status. This finding suggests that PR status may be related to the heterogeneity in hormonal environments associated with breast cancer risk.

Risk factors for hormone receptor-defined breast cancer in postmenopausal women

The effect of classic breast cancer risk factors on hormone receptor-defined breast cancer is not fully clarified. We explored these associations in a Swedish population-based study. Postmenopausal women ages 50 to 74 years, diagnosed with invasive breast cancer during 1993 to 1995, were compared with 3,065 age frequency-matched controls. We identified 332 estrogen receptor (ER-) and progesterone receptor (PR-) negative, 286 ER+PR-, 71 ER-PR+, 1,165 ER+PR+, and 789 tumors with unknown receptor status. Unconditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). Women ages >or=30 years, compared with those ages 20 to 24 years at first birth, were at an increased risk of ER+PR+ tumors (OR, 1.5; 95% CI, 1.2-1.8) but not ER-PR- tumors (OR, 1.1; 95% CI, 0.8-1.6). Women who gained >or=30 kg in weight during adulthood had an approximately 3-fold increased relative risk of ER+PR+ tumors (OR, 2.7; 95% CI, 1.9-3.8), but no risk increase of ER-PR- tumors (OR, 1.0; 95% CI, 0.5-2.1), compared with women who gained <10 kg. Compared with never users, women who used menopausal estrogen-progestin therapy for at least 5 years were at increased risk of ER+PR+ tumors (OR, 3.0; 95% CI, 2.1-4.1) but not ER-PR- tumors (OR, 1.3; 95% CI, 0.7-2.5). In conclusion, other risk factors were similarly related to breast cancer regardless of receptor status, but high age at first birth, substantial weight gain in adult age, and use of menopausal estrogen-progestin therapy were more strongly related to receptor-positive breast cancer than receptor-negative breast cancer.

Body weight and postmenopausal breast cancer risk defined by estrogen and progesterone receptor status among Swedish women: A prospective cohort study

Although obesity is one of the established risk factors for postmenopausal breast cancer, it is not clear whether this positive association differs across estrogen receptor (ER) and progesterone receptor (PR) status of breast tumors. We evaluated the association between body weight and ER/PR defined breast cancer risk stratified by postmenopausal hormone (PMH) use and a family history of breast cancer in the population-based Swedish Mammography Screening Cohort comprising 51,823 postmenopausal women. Relative body weight was measured by body mass index (kg/m2) based on self-reported weight and height collected in 1987 and 1997. Relative risks (RRs) were estimated by hazard ratios derived from Cox proportional hazards regression models. During an average of 8.3-year follow-up, 1,188 invasive breast cancer cases with known ER and PR status were diagnosed. When comparing to normal weight group, we observed a positive association between obesity and risk for the development of ER+ PR+ tumors (RR = 1.67, 95% CI = 1.34-2.07) and an inverse association for the development of all PR- tumors (RR = 0.68, 95% CI = 0.47-0.98). Statistically significant heterogeneity was observed in the RRs between ER+ PR+ tumors and all PR- tumors (p(heterogeneity) < 0.0001). The positive association of obesity with the development of ER+ PR+ tumors was confined to never-users of PMHs (RR = 1.90 (CI 95%:1.38-2.61)) and to those without a family history of breast cancer (RR = 1.82 (CI 95%:1.45-2.29)). Our results support the hypothesis that excess endogenous estrogen due to obesity contributes to an increased risk of ER+ PR+ postmenopausal breast cancer.

What can be learnt from models of incidence rates?

Models of breast cancer incidence have evolved from the observation by Armitage and Doll in the 1950s that the pattern of incidence by age differs for reproductive cancers from those of other major malignancies. Both two-stage and multistage models have been applied to breast cancer incidence. Consistent across modeling approaches, risk accumulation or the rate of increase in breast cancer incidence is most rapid from menarche to first birth. Models that account for the change in risk after menopause and the temporal sequence of reproductive events summarize risk efficiently and give added insights to potentially important mechanistic features. First pregnancy has an adverse impact on progesterone receptor negative tumors, while increasing parity reduces the risk of estrogen/progesterone receptor positive tumors but not estrogen/progesterone receptor negative tumors. Integrated prediction models that incorporate prediction of carrier status for highly penetrant genes and also account for lifestyle factors, mammographic density, and endogenous hormone levels remain to be efficiently implemented. Models that both inform and reflect the emerging understanding of the molecular and cell biology of carcinogenesis are still a long way off.

Association of physical activity with hormone receptor status: the Shanghai Breast Cancer Study

Evidence exists that breast tumors differing by estrogen receptor (ER) and progesterone receptor (PR) status may be phenotypically distinct diseases resulting from dissimilar etiologic processes. Few studies have attempted to examine the association of physical activity with breast cancer subtype. Such research may prove instructive into the biological mechanisms of activity. Consequently, this investigation was designed to assess the relationship between physical activity and hormone receptor-defined breast cancers in a population of Asian women in which the distribution of receptor types differed from traditional Western populations. Participants, ages 25 to 64 years, were recruited into this population-based, case-control study of breast cancer conducted in Shanghai, China from August 1996 to March 1998. Histologically confirmed breast cancer cases with available receptor status information (n = 1001) and age frequency-matched controls (n = 1,556) completed in-person interviews. Polytomous logistic regression was used to model the association between measures of activity with each breast cancer subtype (ER+/PR+, ER-/PR-, ER+/PR-, and ER-/PR+) using the control population as the reference group. Exercise in both adolescence and the last 10 years was associated with a decreased risk of both receptor-positive (ER+/PR+) and receptor-negative (ER-/PR-) breast cancers in both premenopausal and postmenopausal women (odds ratios, 0.44 and 0.51 and 0.43 and 0.21, respectively). Sweating during exercise within the last 10 years was also associated with decreased risk for receptor-positive and receptor-negative breast cancers among postmenopausal women (odds ratios, 0.58 and 0.28, respectively). These findings suggest that physical activity may reduce breast cancer risk through both hormonal and nonhormonal pathways.

Breast cancer risk factors according to joint estrogen receptor and progesterone receptor status

BACKGROUND

We investigated risk factor patterns for subtypes of breast cancer characterized by joint estrogen receptor (ER) and progesterone receptor (PR) status in a hospital-based case-control study.

METHODS

ER and PR tumor status were determined immunohisotchemically. Risk factors of interest were entered into a multiple polychotomous logistic regression model simultaneously; odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Using this model, cases in the four tumor subtypes (ER+PR+, ER-PR-, ER+PR-, ER-PR+) were compared simultaneously to controls. A Wald test for heterogeneity across the four subtypes was conducted, as well as a case-case comparison between the two most biologically disparate subtypes, ER+PR+ and ER-PR-.

RESULTS

The receptor status distribution was as follows: 33% ER+PR+, 34% ER-PR-, 20% ER+PR-, and 13% ER-PR+. Among 317 cases and 401 controls, we found significant heterogeneity across the four tumor subtypes for older age at first full-term pregnancy (p=0.04) and post-menopausal status (p=0.04). For older age at first full-term pregnancy, an elevated risk was found for the ER+PR- subtype (OR=2.5; 95% CI: 1.2-5.1). For post-menopausal status, elevated risks were found for both the ER+PR+ (OR=2.4; 95% CI: 1.1-4.9) and ER+PR- (OR=7.2; 95% CI: 2.4-21.7) subtypes. From the case-case comparisons, we found that cases, who had consumed alcohol for more than 1 year were 3.4 times more likely to have ER+PR+ tumors than ER-PR- tumors (95% CI: 1.4-8.4).

CONCLUSIONS

Certain breast cancer risk factors may vary by ER and PR status, and joint ER/PR status should be taken into account in future studies of risk factor estimates.

Etiology of Hormone Receptor–Defined Breast Cancer: A Systematic Review of the Literature

Breast cancers classified by estrogen receptor (ER) and/or progesterone receptor (PR) expression have different clinical, pathologic, and molecular features. We examined existing evidence from the epidemiologic literature as to whether breast cancers stratified by hormone receptor status are also etiologically distinct diseases. Despite limited statistical power and nonstandardized receptor assays, in aggregate, the critically evaluated studies (n = 31) suggest that the etiology of hormone receptor–defined breast cancers may be heterogeneous. Reproduction-related exposures tended to be associated with increased risk of ER-positive but not ER-negative tumors. Nulliparity and delayed childbearing were more consistently associated with increased cancer risk for ER-positive than ER-negative tumors, and early menarche was more consistently associated with ER-positive/PR-positive than ER-negative/PR-negative tumors. Postmenopausal obesity was also more consistently associated with increased risk of hormone receptor–positive than hormone receptor–negative tumors, possibly reflecting increased estrogen synthesis in adipose stores and greater bioavailability. Published data are insufficient to suggest that exogenous estrogen use (oral contraceptives or hormone replacement therapy) increase risk of hormone-sensitive tumors. Risks associated with breast-feeding, alcohol consumption, cigarette smoking, family history of breast cancer, or premenopausal obesity did not differ by receptor status. Large population-based studies of determinants of hormone receptor–defined breast cancers defined using state-of-the-art quantitative immunostaining methods are needed to clarify the role of ER/PR expression in breast cancer etiology.

Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83?000 women with breast cancer from 16 countries

BACKGROUND

The Collaborative Group on Hormonal Factors in Breast Cancer has brought together the worldwide epidemiological evidence on the possible relation between breast cancer and previous spontaneous and induced abortions.

METHODS

Data on individual women from 53 studies undertaken in 16 countries with liberal abortion laws were checked and analysed centrally. Relative risks of breast cancer--comparing the effects of having had a pregnancy that ended as an abortion with those of never having had that pregnancy--were calculated, stratified by study, age at diagnosis, parity, and age at first birth. Because the extent of under-reporting of past induced abortions might be influenced by whether or not women had been diagnosed with breast cancer, results of the studies--including a total of 44000 women with breast cancer--that used prospective information on abortion (ie, information that had been recorded before the diagnosis of breast cancer) were considered separately from results of the studies--including 39000 women with the disease--that used retrospective information (recorded after the diagnosis of breast cancer).

FINDINGS

The overall relative risk of breast cancer, comparing women with a prospective record of having had one or more pregnancies that ended as a spontaneous abortion versus women with no such record, was 0.98 (95% CI 0.92-1.04, p=0.5). The corresponding relative risk for induced abortion was 0.93 (0.89-0.96, p=0.0002). Among women with a prospective record of having had a spontaneous or an induced abortion, the risk of breast cancer did not differ significantly according to the number or timing of either type of abortion. Published results on induced abortion from the few studies with prospectively recorded information that were not available for inclusion here are consistent with these findings. Overall results for induced abortion differed substantially between studies with prospective and those with retrospective information on abortion (test for heterogeneity between relative risks: chi2(1) =33.1, p<0.0001).

INTERPRETATION

Pregnancies that end as a spontaneous or induced abortion do not increase a woman's risk of developing breast cancer. Collectively, the studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions.

Risk factors for breast cancer according to estrogen and progesterone receptor status

BACKGROUND

Evaluations of epidemiologic risk factors in relation to breast cancer classified jointly by estrogen receptor (ER) and progesterone receptor (PR) status have been inconsistent. To address this issue, we conducted a prospective evaluation of risk factors for breast cancer classified according to receptor status.

METHODS

During 1 029 414 person-years of follow-up of 66 145 women participating in the Nurses' Health Study from 1980 through 2000, we identified 2096 incident cases of breast cancer for which information on ER/PR status was available: 1281 were ER+/PR+, 318 were ER+/PR-, 80 were ER-/PR+, and 417 were ER-/PR-. We fit a log-incidence model of breast cancer and used polychotomous logistic regression to compare coefficients for breast cancer risk factors in patients with different ER/PR status. To test for differences in risk factor odds ratios based on marginal ER/PR categories, we evaluated ER status controlling for PR status and vice versa. The predictive ability of our log-incidence model to discriminate between women who would develop ER+/PR+ breast cancer and those who would not (and similarly for ER-/PR- breast cancer) was evaluated by using receiver operator characteristic curve analysis. All statistical tests were two-sided.

RESULTS

We observed statistically significant heterogeneity among the four ER/PR categories for some risk factors (age, menopausal status, body mass index [BMI] after menopause, the one-time adverse effect of first pregnancy, and past use of postmenopausal hormones) but not for others (benign breast disease, family history of breast cancer, alcohol use, and height). The one-time adverse association of first pregnancy with incidence was present for PR- but not for PR+ tumors after controlling for ER status (P =.007). However, the association of BMI after menopause with incidence was present for PR+ but not PR- tumors (P =.005). Statistically significant differences in the incidence of ER+ and ER- tumors were seen with age, both before and after menopause (P =.003), and with past use of postmenopausal hormones (P =.01). Area under the receiver operator characteristic curve, adjusted for age, was 0.64 (95% confidence interval [CI] = 0.63 to 0.66) for ER+/PR+ tumors and 0.61 (95% CI = 0.58 to 0.64) for ER-/PR- tumors.

CONCLUSIONS

Incidence rates and risk factors for breast cancer differ according to ER and PR status. Thus, to accurately estimate breast cancer risk, breast cancer cases should be divided according to the ER and PR status of the tumor.

Obesity, tamoxifen use, and outcomes in women with estrogen receptor-positive early-stage breast cancer

BACKGROUND

Obesity is associated with both increased breast cancer risk and poorer prognosis after disease onset. However, little is known about the effect of obesity on treatment efficacy. We evaluated the association of obesity with outcomes and with tamoxifen efficacy in women with early-stage, hormone-responsive breast cancer participating in a multicenter cancer cooperative group clinical trial.

METHODS

The cohort consisted of 3385 women enrolled in National Surgical Adjuvant Breast and Bowel Project (NSABP) protocol B-14, a randomized, placebo-controlled trial evaluating tamoxifen for lymph node-negative, estrogen receptor (ER)-positive breast cancer. Hazards of breast cancer recurrence, contralateral breast tumors, other new primary cancers, and several mortality endpoints were evaluated in relation to body mass index (BMI), using statistical modeling to adjust for other prognostic factors. Median follow-up time was 166 months. All statistical tests were two-sided.

RESULTS

The hazard of breast cancer recurrence was the same among obese (BMI > or =30.0 kg/m2) women as compared with underweight and normal-weight women (BMI <25.0; hazard ratio [HR] = 0.98, 95% confidence interval [CI] = 0.80 to 1.18). Contralateral breast cancer hazard was higher in obese women than in underweight/normal-weight women (HR = 1.58, 95% CI = 1.10 to 2.25), as was the risk of other primary cancers (HR = 1.62, 95% CI = 1.16 to 2.24). Compared with normal-weight women, obese women had greater all-cause mortality (HR = 1.31, 95% CI = 1.12 to 1.54) and greater risk of deaths due to causes unrelated to breast cancer (HR = 1.49, 95% CI = 1.15 to 1.92). Breast cancer mortality was not statistically significantly increased for obese women (HR = 1.20, 95% CI = 0.97 to 1.49). Tamoxifen reduced breast cancer recurrence and mortality, regardless of BMI.

CONCLUSIONS

For women with lymph node-negative, ER-positive breast cancer, obesity was not associated with a material increase in recurrence risk or a change in tamoxifen efficacy. However, because obesity was associated with increased risks of contralateral breast cancer, of other primary cancers, and of overall mortality, it may influence long-term outcomes for breast cancer survivors.

Alcohol, tobacco and breast cancer--collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 women without the disease

Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58,515 women with invasive breast cancer and 95,067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19-1.45, P<0.00001) for an intake of 35-44 g per day alcohol, and 1.46 (1.33-1.61, P<0.00001) for >/=45 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5-8.7%; P<0.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1% per 10 g per day, P<0.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers=1.03, 95% CI 0.98-1.07, and for current smokers=0.99, 0.92-1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver.

Hormone receptors in breast cancer: racial differences in distribution and survival

The purpose of this study was to describe hormone receptor status and analyze the effect of receptors on survival from breast cancer. Comparisons were made between African-American and Caucasian racial categories. Breast cancer data from 1990 through 1997 collected by the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program were analyzed. Subjects were 993 Caucasian men, 12,303 African-American women, and 141,045 Caucasian women. The number of African-American men was too small to analyze separately (n = 93). In addition to analysis of estrogen and progesterone receptor status by sex and race, tumor and patient characteristics included age, stage at time of diagnosis, and tumor histology. The proportion of Caucasian men with hormone receptor positive tumors remained relatively high and stable for all ages. In women, the proportion of hormone receptor positive tumors increased with age, with African-American women having the highest proportion of hormone receptor negative tumors. Caucasian men had highest proportions of hormone receptor positive tumors in all histology and stage groups, while African-American women had lowest proportions of hormone receptor positive tumors in all stage and histologic categories. Survival for African-American women was significantly worse for each hormone receptor category. In multivariate analyses, race was a significant independent predictor of survival, but sex was not. Although reasons for differences in hormone receptor status by sex and race are unknown, several hypotheses are discussed with respect to differences in tumor histopathology and risk factors.

Organochlorine exposures influence on breast cancer risk and survival according to estrogen receptor status: a Danish cohort-nested case-control study

BACKGROUND

The relationship between breast cancer and organochlorine exposure is controversial and complex. As estrogen receptor positive and negative breast cancer may represent different entities of the disease, this study was undertaken to evaluate organochlorines influence on breast cancer risk and survival according to receptor status.

METHODS

The background material stems from the Copenhagen City Heart Study (Denmark 1976-78). The breast cancer risk was investigated in a cohort nested case-control design including 161 cases and twice as many breast cancer free controls. The cases served as a cohort in the survival analysis. Serum organochlorine concentrations were determined by gaschromotography.

RESULTS

The observed increased breast cancer risk associated with exposure to dieldrin derived from women who developed an estrogen receptor negative (ERN) tumor (Odds ratio [OR] I vs. IV quartile, 7.6, 95% confidence interval [95% CI] 1.4-46.1, p-value for linear trend 0.01). Tumors in women with the highest dieldrin serum level were larger and more often spread at the time of diagnosis than ERP tumors. The risk of dying was for the remaining evaluated compounds higher among patients with ERP breast cancer when compared to those with ERN. In the highest quartile of polychlorinated biphenyls (SigmaPCB) it was more than 2-fold increased (Relative risk [RR] I vs. IV quartile, 2.5, 95% CI 1.1-5.7), but no dose-response relation was apparent.

CONCLUSION

The results do not suggest that exposure to potential estrogenic organochlorines leads to development of an ERP breast cancer. A possible adverse effect on prognosis of hormone-responsive breast cancers needs to be clarified.

Reproductive factors and breast cancer in New Zealand

A national population-based case-control study was used to assess the influence on breast cancer risk of reproductive factors and the possibility of an interaction with age at diagnosis. A total of 891 women aged 25 to 54 with a first diagnosis of breast cancer, and 1864 control subjects, randomly selected from the electoral rolls, were interviewed. There was a declining risk of breast cancer with increasing age at menarche (p = 0.06), the strongest effect being seen in women aged less than 40. Parous women had a 27% lower risk of breast cancer than nulliparous women, a reduced risk being evident in all but the youngest age group. A falling risk of breast cancer with rising parity was clear only in women diagnosed when aged at least 45 years. Breast cancer risk tended to fall amongst parous women with increasing duration of breastfeeding (p = 0.14); the association was most apparent in the youngest women, while those over 40 years at diagnosis showed no clear negative trend. There was no association of breast cancer risk with age at first full-term pregnancy, time since last full-term pregnancy, abortion (spontaneous or induced), abortion before first full-term pregnancy, or ability to conceive, and there was no trend in risk with age at natural menopause. Women in the highest category of body mass index at age 20 had the lowest risk of breast cancer in the age group studied. When each reproductive factor was formally tested for effect modification by age at diagnosis, the interaction term in logistic models approached statistical significance only for parity (p = 0.07).

A review on family history of breast cancer: screening and counseling proposals for women with familial (non-hereditary) breast cancer

With the aim to specify screening recommendations for women with familial (non-hereditary) breast cancer (FBC) we analysed 59 studies using quantitative methods of pooling. The pooled relative risk (RR) and cumulative probability were used to estimate breast cancer risk. The RRs for women with a family history of breast cancer in a first-degree relative was 2.03 (95% CI 1.09-2.22). The highest RR is observed for women with a family history and atypical hyperplasia in their breast biopsy specimen (RR = 10.87, 95% CI 6.05-19.69). A high cumulative probability before the age of 50 was only found for women with a combination of two risk factors: a family history and atypical hyperplasia, namely 19% (95% CI 11-33%). The cumulative probabilities of women aged 50 to 70 years who have a family history were between 11% (95% CI 9-13%, a family history in combination with age at first birth before 22 years) and 53% (95% CI 35-75%, a family history in combination with atypical hyperplasia). These high risks suggest that women over 50 years of age who have a family history of FBC have to be actively encouraged to participate in a screening program consisting of a biannual palpation by a specialist, an annual mammogram and a monthly self-control. Yearly screening is recommended for women under 50 years of age who have a family history and atypical hyperplasia. These recommendations remain valid until the effectiveness of such screening programs is assessed.

Estrogen receptor status of breast cancer: a marker of different stages of tumor or different entities of the disease?

Breast cancer can be divided into two types according to the estrogen receptor (ER) level of the tumor: ER-positive and ER-negative. Two hypotheses have been raised about the relationship between ER-positive and ER-negative breast tumors. One hypothesis considers ER status as an indicator of a different stage of the disease. The other regards ER-positive and ER-negative tumors as different entities. For both etiological and biological studies of breast cancer it is important to know which hypothesis is correct. In this paper, we review evidence for and against each hypothesis and suggest issues to be addressed in future studies.

Association between family history of cancer and breast cancer defined by estrogen and progesterone receptor status

There are recent data to suggest that risk factors for breast cancer may differ according to whether the tumor expresses detectable levels of the estrogen receptor (ER) and progesterone receptor (PR). While a family history of breast cancer is one of the most consistent predictors of the disease, we recently reported a modest inverse association with ER+PR- tumors. However, the definition of a family history of cancer did not consider second-degree relatives or cancer sites that may be etiologically related. The current report presents additional data analysis from the Iowa Women's Health Study, a prospective population-based cohort study conducted among 41,837 postmenopausal women. At baseline in 1986, respondents provided information on family history of cancers of the breast, ovaries, or uterus/endometrium in their mothers, sisters, daughters, maternal and paternal grandmothers, and maternal and paternal aunts. Data on family history of prostate cancer in fathers and brothers and age at onset of breast cancer in mothers and sisters were collected in 1992. Cohort members were followed for cancer incidence through the statewide tumor registry. After 7 years and more than 235,000 person-years of follow-up, 939 incident cases of breast cancer were identified. Information was obtained from the tumor registry on ER (+/-) and PR (+/-) status for 610 cases (65.0%). A family history of breast cancer in first-degree relatives was associated with increased risk (relative risk [PR] = 1.4; 95% confidence interval [CI]: 1.1-1.6) for all receptor-defined subtypes of breast cancer except ER+PR- tumors (RR = 0.7; 95% CI: 0.3-1.4). These results were unchanged when data on second-degree relatives were included. When the onset of breast cancer in relatives occurred at or before the age of 45 years, increased risks were evident only for ER-PR+ and ER-PR- tumors (RR = 2.3 and 3.3, respectively). Conversely, when relatives were affected with breast cancer after the age of 45 years, increased risks were most apparent for ER+PR+ and ER-PR+ tumors (RR = 1.3 and 3.2, respectively). A family history of prostate cancer in first-degree relatives was associated with a 1.2-fold increased risk of breast cancer (95% CI: 0.98-1.50), largely a reflection of the association with ER-PR- tumors (RR = 1.5; 95% CI: 0.8-3.0). The small numbers of cases in some categories and the corresponding wide CIs preclude definitive conclusions, but these data are at least suggestive that joint stratification of breast tumors on ER and PR status may be useful in partitioning breast cancer families into more homogeneous subsets.

Reproductive factors and breast cancer risk. Effect of age at diagnosis

The data from a French case-control study of 495 patients with breast cancer and 542 control subjects interviewed in five French public hospitals, were analyzed to assess the effect of reproductive factors (age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity) on the risk of breast cancer. Age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity appeared to have a limited influence on breast cancer risk. However, the relationship between these factors and the risk of breast cancer varied according to the age at breast cancer diagnosis. In the youngest group of women, the most consistent effects came from factors occurring early in life (menarche, first full-term pregnancy, and consequently the time interval between these two events). These factors had a null or weak effect on the oldest group of women. The protective effect of high parity was confined to the oldest group of women.

Reproductive and menstrual factors in relation to mammographic parenchymal patterns among perimenopausal women

The relationship between mammographic patterns and reproductive and menstrual factors was examined in 3640 Norwegian women, aged 40-56 years, participating in the Third Tromsö study conducted in 1986-87. Epidemiological data were obtained from questionnaires. The mammograms were categorised into five groups. This categorisation is based on anatomic-mammographic correlations, following three-dimensional (thick slice technique) histopathologic-mammographic comparisons, rather than simple pattern reading. Patterns 1-3 were combined into a low-risk group and patterns 4 and 5 into a high-risk group for analysis. Women who had more than four children were 90% less likely to have a high-risk pattern than nulliparous women (OR = 0.09, 95% CI 0.04-0.16) controlling for age, weight, height and menopausal status. Furthermore, those who first gave birth over 34 years of age were more than twice as likely to have a high-risk pattern than those giving birth in their teens (OR = 2.37, 95% CI 1.23-4.56) adjusting for parity. Among post-menopausal women, age at menarche was negatively (P for trend = 0.015) and late age at menopause positively (P for trend = 0.072) related to high-risk patterns. Among premenopausal women, age at menarche was positively related to high-risk patterns (P for trend = 0.001). Also, menopausal status rather than age was associated with high-risk patterns. These findings support the opinion that reproductive and menstrual factors are involved in determining the mammographic parenchymal pattern among perimenopausal women.

A hospital-based case-control study of breast-cancer risk factors by estrogen and progesterone receptor status

It has been proposed that breast cancers may differ in their pathogenesis and etiology according to their estrogen receptor (ER) and progesterone receptor (PR) status. This hospital-based case-control study in Japan assessed the relationship between known and suspected breast-cancer risk factors and ER and PR status. Information on risk factors was collected from histologically confirmed breast-cancer cases (n = 519) and from cancer-free controls (n = 9,506). Of 160 cases with known ER status, 58 percent were ER-positive; 38 percent of 157 cases with known PR status were PR-positive. No statistically significant differences were found between ER-positive cf ER-negative cases. However, statistically significant differences between PR-positive cf PR-negative cases were observed for number of full-term pregnancies (P = 0.01), menstrual regularity as a teenager (P = 0.024), and occupation as housewife (P = 0.036). Borderline differences were observed for age at menopause (P = 0.074), and age at menarche (P = 0.083). This study provides some evidence that etiologic distinctions may be greater between PR-positive and PR-negative breast cancers than between ER-positive and ER-negative breast cancers.

Lifetime menstrual activity--indicator of breast cancer risk

A case-control study of 67 cases of breast cancer and 157 controls was conducted to investigate the role of different behavioral, reproductive, and hormonal factors and to develop a unifying indicator of breast cancer risk. The results confirm previous reports of the influence of smoking on the risk of breast cancer. Age at menarche was found to be a risk factor among the premenopausal women. Late age at menopause was suggestive of an increase in risk. Long use of oral contraceptive or estrogen supplementation were risk-enhancing both pre- and postmenopausally. Lifetime duration of menstrual activity (LMA) combines age at menarche and menopause, parity, and lactation into a biologically plausible model. Our findings concerning LMA support its role as a determinant of breast cancer.

Reproductive factors in breast cancer epidemiology

There is abundant epidemiologic evidence showing that early menarche, late menopause, low parity and late age at first birth are related to increased risk of breast cancer. However, in younger age groups, uniparous women seem to be at higher risk than nulliparous, and the effect of later pregnancies is less clear in this group. Intervals between pregnancies may modify the general protective effect. Some studies have indicated an adverse effect of late age at pregnancies after the first. Further studies are necessary to determine if the general protective effect of pregnancies after the first is preceded by a transient increase in breast cancer risk. No clear association has been established with number of abortions. Results from two large prospective studies suggest that breast feeding is not strongly related to risk of breast cancer among Western populations.

Steroid receptor status and the epidemiology of breast cancer

This case-control study examined risk factors for breast cancer according to tumor estrogen receptor (ER) status and progesterone receptor (PR) status. The data included 607 case patients and 1214 control subjects matched by age and residence. Of 528 case patients with steroid receptor information, 67% had ER-positive tumors and 55% had PR-positive tumors. Odds ratios for ER-positive and ER-negative breast cancer were similar with respect to menopausal status, age at menarche, history of cystic breast disease, and Quetelet Index. Family history of breast cancer was a stronger risk factor for ER-negative than for ER-positive breast cancer and the odds ratios for number of births were suggestive of a different effect. While ER and PR status were highly correlated, there were some differences in their associations with risk factors. Odds ratios for PR-positive and PR-negative breast cancer differed for number of births and were suggestive of differences with respect to menopausal status, Quetelet Index, and family history of breast cancer. These findings do not suggest different causal pathways for ER-positive and ER-negative breast cancer. However, they do indicate that PR status may play a role in the etiology of breast cancer.

High-risk populations as targets for breast cancer prevention trials

Breast cancer risk factors include age; a family history of the disease in first-degree relatives (particularly if premenopausal with bilateral disease); proliferative benign breast disease with or without atypia; mammographic parenchymal pattern showing glandular, dense, dysplastic, or Wolfe P2 changes; and obesity. Women in these risk groups have annual breast cancer incidence rates 2 to 10 times higher than baseline. Using data from the National Cancer Institute SEER Program, the U.S. 1987 census estimates, and published prevalence and incidence estimates for breast cancer risk factors, estimates were made for the number of women in the white female population who are at increased risk for breast cancer and who might serve as suitable subjects for an antiestrogen chemoprevention intervention trial. More than 30 million white women are older than 50 years. Two million women older than 50 years have at least one first-degree relative with breast cancer. Six million women over age 50 have undergone breast biopsy for benign disease; one-fourth of these women have proliferative changes, and 11% also have a family history of breast cancer. More than 8 million women older than 50 years are obese, and at least a million older women have high-risk mammographic parenchymal patterns. Thus, there are at least 12 million women at increased risk for breast cancer in the United States, and each year 200,000 additional women enter the high-risk pool. These data indicate that sufficient numbers of women at increased risk for breast cancer are present in the population to justify a chemoprevention trial. The optimal recruitment strategy is yet to be identified.

Breast cancer

Breast cancer will affect 1 out of 10 women in the United States and cause 27 deaths per 100,000 women per year. The etiology remains unknown, but the incidence correlates with genetic as well as environmental factors. Screening programs have been shown to prolong the survival by early detection compared with control populations but remain underutilized by physicians and patients. Breast disease can be evaluated by physical examination and mammography and a definitive diagnosis made by needle aspiration, needle biopsy, or excisional biopsy. This allows the patient to participate in the decision regarding mastectomy vs. conservative surgery plus radiation therapy. These two approaches have equivalent survival in selected patients. Patients with locally advanced, nonmetastatic disease benefit from a multidisciplinary approach using preoperative chemotherapy and postoperative radiation therapy. This approach has allowed less disfiguring surgery and improved survival. Preinvasive carcinoma is diagnosed more frequently with the increased use of screening mammography. Local therapy options include simple mastectomy, local excision plus radiation, or local excision alone. The natural history and results of therapy in preinvasive disease are evolving as more data are accumulated. Systemic adjuvant therapy is recommended for all node-positive patients and most node-negative patients with invasive cancer. The specific modality (hormonal or cytotoxic) varies with the subgroup involved. Treatment of metastatic disease to palliate symptoms and prolong survival includes the use of local therapies (surgery and radiation) and hormonal and cytotoxic agents. Most patients benefit, but cure has been unobtainable. Newer approaches utilizing high-dose chemotherapy and bone marrow support with growth factors or autologous transplantation are currently being explored.

Risk factors for breast cancer according to age at diagnosis in a French case-control study

In a French case-control study of 1010 women with breast cancer and 1950 controls with nonmalignant disease, the variations of the effects of 8 risk factors for breast cancer as a function of age at diagnosis, were analysed by tests of homogeneity and trend. The risks associated with a late age at first full-term pregnancy and with nulliparity were different between age-groups (test of homogeneity: p = 0.03), and the highest risks for these two factors were observed in women 45-54 years old. The risks associated with Quetelet index were also found to vary with age at diagnosis (test for trend: p = 0.008). A high Quetelet index decreased the risk of breast cancer in the younger age-groups; this decrease of risk became progressively less important with advancing age, and no such effect was found in the oldest age-group. Inverse results were observed for a tall stature (test for trend: p = 0.04): a tall stature increased the risk of breast cancer in the younger age-groups, and the figures suggested a reverse effect in the oldest group. No large variation with age was found for the effects of age at menarche, history of breast cancer death in mother or sisters, prior biopsy for benign breast disease, and weight. In conclusion, the relative importance of certain risk factors for breast cancer is closely related to age at diagnosis. Nulliparity and a late age at first birth appear to be major risk factors only for middle-aged women, whereas a low Quetelet index and a tall stature appear to increase the risk of breast cancer only for younger women.

Leanness, peptide hormones and premenopausal breast cancer

Environmental factors promote the development of and decrease survival from Breast Cancer. Prospective morphological and hormonal studies indicate biological markers for this disease are evident in premenopausal women. The majority of premenopausal patients are non-obese (Body Mass Index, BMI less than 25). Lean women have a greater proportion of estrogen receptor negative (ER-) tumours, which may grow faster and have a higher concentration of epithelial growth factor (EGF). We have reported that lean, BMI less than 23, versus obese, BMI greater than 28, women have a different gut-pancreatic peptide hormone response to meals and that differences in these peptide hormones occur between healthy and age weight matched premenopausal patients. We hypothesize that the diet peptide hormone control of food intake in lean women is associated with the development of mammary dysplasia, change in growth factor profile and steroid hormone metabolism.

Risk factors for breast cancer by oestrogen receptor status: a population-based case-control study

Data from a population-based case-control study conducted in Adelaide, South Australia, and involving 451 case-control pairs, were analysed to determine whether the associations of menstrual, reproductive, dietary and other factors with risk of breast cancer differed by oestrogen receptor (ER) status. Data on ER status were available for 380 cases. The proportion of tumours which were ER+ increased with age, and there was a higher proportion of ER+ tumours in post-menopausal than in premenopausal women. Both oral contraceptive use (P = 0.055) and cigarette smoking (P = 0.047) were associated with increased (unadjusted) risk of ER- cancer, while having little association with risk of ER+ cancer. Most dietary factors had little association with risk of either cancer type, the main exception being the reduction in risk of ER- breast cancer with increasing beta-carotene intake (P for trend = 0.017). In general, however, links with the factors examined were not strong enough to suggest different causal pathways for ER- and ER+ breast cancer.

Menstrual factors and breast cancer risk

Relationships between menstrual factors and breast cancer risk were investigated in a prospective study of 63,090 Norwegian women. A total of 1565 cases of breast cancer occurred during follow-up from 1961 through 1980. The risk of breast cancer decreased with increasing age at menarche (P = 0.06) and increased with increasing age at menopause (P = 0.005) in analyses adjusted for age, urban/rural place of residence, parity, and age at first and last birth. The results correspond to an average increase in breast cancer risk of 4.0% for each year of decrease in age at menarche, and an increase in risk of 3.6% for each year of increase in age at menopause. The protective effect of early menopause was strongest for breast cancer diagnosed in patients 80 years of age or older. No clear relationship was seen between menstrual irregularities and breast cancer risk.

Risk of breast cancer in relation to reproductive factors in Denmark

The effect of reproductive factors on breast cancer risk was evaluated in a population-based case-control study, including 1,486 breast cancer cases diagnosed over a one-year period in Denmark. They were identified from the files of the nationwide trial of the Danish Breast Cancer Co-operative group and the Danish Cancer Registry. The control group was an age-stratified random sample of 1,336 women from the general population. Data on risk factors were collected by self-administered (mailed) questionnaires. Significantly increased relative risks (RR) were associated with never being pregnant (RR = 1.47), an early terminated first pregnancy (RR = 1.43), and having a natural menopause after the age of 54 (RR = 1.67). Trends of decreasing risk were observed by increasing parity and age at menarche. These findings were independent of age at first full-term pregnancy which overall was not related to breast cancer risk, though a weak association appeared in women less than 50 years at diagnosis. The study confirmed that pregnancies must continue to term to offer protection against breast cancer.

Endogenous sex hormone levels and breast cancer risk

Sex-steroid hormones are a major determinant of the risk of breast cancer. We evaluated the relationship between obesity and endogenous estrogen levels in 79 healthy, postmenopausal women. Thirty-nine of the women were siblings of patients with postmenopausal-onset breast cancer; the remaining women were age-matched (+/- 10 yr) controls. Our hypothesis was that the siblings of the breast cancer patients would weigh more and that this excess weight would lead to higher serum estrone levels. The choice of unaffected family members of breast cancer patients reduces the concern that results may have been influenced by the cancer rather than antecedent to its development. Our findings demonstrated a statistically significant excess estrone level in the siblings compared to the controls (58.9 vs 47.8 pg/ml, P = 0.005). The siblings weighed 4.3 kg more than the controls. Matched pairs analysis (sibling-control), adjusting for weight, also showed significant differences in serum estrone levels. These differences were observed despite comparability in dietary intake, medication use, and personal medical history. These findings represent the first time that higher estrogen levels have been measured in siblings of postmenopausal breast cancer patients. This observation may represent an important link in our understanding of the relationship between genetic and environmental risk factors of breast cancer. One approach to subsequent genetic studies of breast cancer may be to focus on the possible biological determinants such as sex-steroid hormone level receptors, oncogenes, and gene products and not on the "familial aggregation" of breast cancer.