Pooled analysis of prospective cohort studies on height, weight, and breast cancer risk

Obesity and breast cancer: a review of the literature

A woman's build, the risk of breast cancer and its subsequent prognosis seem to be related. In most but not all case-control and prospective cohort studies, an inverse relationship has been found between weight and breast cancer among premenopausal women. However, most large epidemiological studies have found that overweight or obese women are at increased risk of developing postmenopausal breast cancer. It is suggested that higher body mass index is associated with a more advanced stage of breast cancer at diagnosis in terms of tumour size but data on lymph node status is not so consistent. All treatment modalities for breast cancer such as surgery, radiotherapy, chemotherapy and hormonal treatment may be adversely affected by the presence of obesity. The overall and disease-free survival is worse in most but not all studies of prognosis of obese pre- and postmenopausal women with breast cancer.

Weight Change and the Risk of Late-Onset Breast Cancer in the Original Framingham Cohort

OBJECTIVE

Adult weight gain has been associated with a twofold risk of postmenopausal breast cancer. Data are limited regarding whether weight gain at specific periods of marked changes in estrogen- and insulin-related hormones have different risk associations. This study assesses the relation of adult weight change overall and at specific, hormonally relevant times with diagnosis of a first breast cancer after age 55 (late onset).

METHODS

Framingham study data were used to assess premenopausal (25-44 yr), perimenopausal (45-55 yr), postmenopausal (after 55 yr), and adult lifetime (from 25 yr) weight change in relation to late-onset breast cancer in 2,873 women followed for up to 48 yr, with 206 late-onset breast cancers.

RESULTS

Adult lifetime weight gain was associated with an increased risk of late-onset breast cancer (P trend = 0.046). Weight gain during specific time periods was not associated with breast cancer. Data suggested a possible decreased risk of breast cancer with weight loss from ages 25 to 44 and 45 to 55 yr (relative risk = 0.4 [0.2-1.2] and 0.5 [0.3-0.9], respectively).

CONCLUSION

These data confirm prior reports of an association between adult lifetime weight gain and increased risk of late-onset breast cancer and support current recommendations to avoid adult weight gain.

Cancer control in women. Update 2003

The global cancer burden in women appeared to be increasing quickly at the end of the twentieth century with notable increases in the absolute numbers of cases of breast, cervix, lung and colorectal cancer of concern. However, prospects for cancer control in women appear to be good within our current knowledge and deserve close attention. Rates of lung cancer in women are increasing substantially in many countries and seem set to overtake breast cancer as the commonest form of cancer death in women in many parts of the world. These changes are due to the effects of cigarette smoking, a habit which women widely embraced during the second half of the last century. The high levels of smoking current in young women, which have yet to have their full inpact on death rates, constitute an important hazard not only for future cancer risks but for several other important causes of death. Although the breast is the commonest form of cancer in women in most western countries, the etiology of this disease remains elusive and preventable causes remain to be identified. Endogenous hormones also appear to have a role in cancer risk in women: oral contraceptives seem to increase slightly the risk of breast cancer in users in the use, and in the immediate post-use, period, but ten years after cessation the risk returns to that of never users. Oral contraceptive usage also appears to be protective against ovarian and endometrial cancer. The use of Hormonal Replacement Therapy (HRT) appears to increase the risk of endometrial cancer and a positive association with breast cancer risk appears to exist. Within the current knowledge of the epidemiology of cancer in women, the most important Cancer Control strategy is the prevention of cigarette smoking and the increase in the prevalence of adult women quitting smoking. Screening has also shown to be effective in reducing incidence and mortality of cervix cancer and mortality from breast and colorectal cancer. Although more work is needed, it is becoming clear that there could be an important role of HPV testing to further enhance cervix cancer screening.

Leptin induces, via ERK1/ERK2 signal, functional activation of estrogen receptor alpha in MCF-7 cells

Leptin is a hormone with multiple biological actions, produced predominantly by adipose tissue. In humans, plasma levels correlate with total body fat, and high concentrations occur in obese women. Among its functions, leptin is able to stimulate normal and tumor cell growth. We demonstrated that leptin induces aromatase activity in MCF-7 cells evidencing its important role in enhancing in situ estradiol production and promoting estrogen-dependent breast cancer progression. Estrogen receptor alpha (ERalpha), which plays an essential role in breast cancer development, can be transcriptionally activated in a ligand-independent manner. Taking into account that unliganded ERalpha is an effector of mitogen-activated protein kinase (MAPK) signal and that leptin is able, via Janus kinase, to activate the Ras-dependent MAPK pathway, in the present study we investigate the ability of leptin to transactivate ERalpha. We provided evidence that leptin is able to reproduce the classic features of ERalpha transactivation in a breast cancer cell line: nuclear localization, down-regulation of its mRNA and protein levels, and up-regulation of a classic estrogen-dependent gene such as pS2. Transactivation experiments with a transfected reporter gene for nuclear ER showed an activation of ERalpha either in MCF-7 or in HeLa cells. Using a dominant negative ERK2 or the MAPK inhibitor PD 98059, we showed that leptin activates the ERalpha through the MAPK pathway. The N-terminal transcriptional activation function 1 appears essential for the leptin response. Finally, it is worth noting that leptin exposure potentates also the estradiol-induced activation of ERalpha. Thus, we are able to demonstrate that the amplification of estrogen signal induced by leptin occurs through an enhancing in situ E(2) production as well as a direct functional activation of ERalpha.

The Role of Nutrition in the Prevention of Breast Cancer

Nutrition has been widely studied as a leading environmental factor in the prevention of breast cancer (BC). Despite the challenges in relating consumption of specific nutrients to BC risk, particularly in the context of a total diet, many investigators have contributed valuable information. Dietary fat has received the most attention and also created the most uncertainty. Specific types of fat, particularly monounsaturated fat and the ratio of omega-3 to omega-6 fatty acids, demonstrate more potential to influence BC risk. A wide variety of other dietary factors have been studied in relation to BC including total energy, dietary fiber, alcohol, micronutrients, phytochemicals, specific foods, and food constituents. Results of epidemiological studies relating consumption of these dietary factors to BC have increased the knowledge base that provides rationale for various nutritional strategies to contribute to BC prevention.

Anthropometry, breast cancer and menopausal status: Use of repeated measurements over 10 years of follow-up?results of the French E3N women's cohort study

The association between weight, BMI and breast cancer was analyzed on 94,805 women of the E3N cohort according to their menopausal status. Seven hundred eighty-six incident invasive premenopausal breast cancers and 1,522 incident invasive postmenopausal breast cancers occurred during a mean follow-up of 9.7 years. Weight and BMI were updated every 24 months and considered as time-dependent variables. Data were analyzed using multivariate Cox proportional hazards models. Trend RRs of premenopausal breast cancer were 0.97 (0.92-1.01) for a 5 kg increase in weight and 0.96 (0.91-1.01) for a 2 kg/m(2) increase in BMI, adjusted for other known risk factors. Opposite trend RRs were found after menopause: 1.05 (1.02-1.08) for weight and 1.06 (1.02-1.09) for BMI, respectively, for similar increases. Women with a BMI of over 30 kg/m(2) had a RR of premenopausal breast cancer of 0.66 (0.40-1.10) compared to those with a BMI of between 18.5 and 25 kg/m(2). Postmenopausal women with a BMI of over 30 kg/m(2) had a RR of breast cancer of 1.23 (1.00-1.59). The increase in risk of postmenopausal breast cancer with increased weight or BMI was similar whatever the HRT used, although the point estimates were higher in HRT users. We strongly recommend to use anthropometric measurements updated during follow-up to assess the effect of weight, BMI on breast cancer risk.

Breast cancer and obesity: an update

Obesity has a complicated relationship to both breast cancer risk and the clinical behavior of the established disease. In postmenopausal women, particularly the elderly, various measures of obesity have been positively associated with risk. However, before menopause increased body weight is inversely related to breast cancer risk. In both premenopausal and postmenopausal breast cancer, the mechanisms by which body weight and obesity affect risk have been related to estrogenic activity. Obesity has also been related to advanced disease at diagnosis and with a poor prognosis in both premenopausal and postmenopausal breast cancer. Breast cancer in African-American women, considering its relationship to obesity, exhibits some important differences from those described in white women, although the high prevalence of obesity in African-American women may contribute to the relatively poor prognosis compared with white American women. Despite the emphasis on estrogens to explain the effects of obesity on breast cancer, other factors may prove to be equally or more important, particularly as they relate to expression of an aggressive tumor phenotype. Among these, this review serves to stress insulin, insulin-like growth factor-I, and leptin, and their relationship to angiogenesis, and transcriptional factors.

Nutrition and breast cancer

The major risk factors for breast cancer are hormone-related, and the only well-established diet-related risk factors for breast cancer are obesity and alcohol consumption. Obesity increases breast cancer risk in postmenopausal women by around 30%, probably by increasing serum concentrations of bioavailable oestradiol. Moderate alcohol intakes increase breast cancer risk by about 7% per alcoholic drink per day, perhaps also by increasing oestrogen levels. Populations with high fat intakes generally have high rates of breast cancer, but studies of individual women have not confirmed an association of high fat diets with breast cancer risk. Phyto-oestrogens can affect hormone metabolism, but data on phyto-oestrogen consumption and breast cancer risk are inconsistent. Nutrition might affect breast cancer risk by altering levels of growth factors such as insulin-like growth factor-I. Current dietary advice should be to avoid obesity, limit alcohol intake, and maintain a varied diet.

Epidemiology of breast cancer – selected highlights

The main risk factors for breast cancer can be usefully grouped into four major categories-family history/genetic, reproductive/hormonal, proliferative benign breast pathology, and mammographic density. These factors are briefly reviewed and quantitative estimaters of risk are given. A computer programme for combining them to produce individualized risk profiles is described. The ongoing IBIS-II trial of chemoprevention for high risk postmenopausal women is presented as one approach to managing high risk women.

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.

Obesity and hormone-dependent tumors: cohort and co-twin control studies based on the Swedish Twin Registry

Obesity increases the risk of certain cancer types, e.g., cancer of the endometrium, colon and gallbladder. For some other cancer forms, e.g., prostate cancer, the association is less clear. We examined the association between body mass index (BMI) and hormone-dependent tumors, utilizing a cohort of 21,884 Swedish twins born during 1886-1925. Information about BMI at different ages and potential confounding factors was collected prospectively. The Swedish Cancer Registry was used to identify cases of cancer in the prostate (n = 666), breast (n = 607), corpus uteri (n = 150) and ovary (n = 118) during 1969-1997. The material was analyzed as a traditional cohort and with co-twin control analyses that allow for control of genetic influences. Obesity (BMI >/=30 kg/m(2)) at baseline was positively associated with cancer in the corpus uteri [relative risk (RR) = 3.03, 95% confidence interval (CI) 1.82-5.03], as was BMI at age 25, independently of BMI at baseline. Increased risk was also found for breast cancer but only in older women (>/=70 years). Overweight at age 25 was associated with decreased risk of breast cancer (RR = 0.51, 95% CI 0.33-0.78). No association was found for prostate cancer. We conclude that age is an important effect modifier of cancer risk associated with obesity and that obesity and overweight in young adult life may affect cancer risk also later in life.

Life-course body size and perimenopausal mammographic parenchymal patterns in the MRC 1946 British birth cohort

Dense mammographic parenchymal patterns are associated with an increased risk of breast cancer. Certain features of body size have been found to be associated with breast cancer risk, but less is known about their relation to breast density. We investigated the association of birth size, childhood growth and life-course changes in body size with Wolfe grade in 1298 perimenopausal women from a British cohort of women born in 1946. The cohort benefits from repeated measures of body size in childhood and adulthood. We obtained mammograms for 90% of women who at age 53 years reported having previously had a mammogram. We found no associations with birth weight or maximum attained height. Body mass index (BMI) at age 53 years and breast size were independently and inversely associated with Wolfe grade (P-value for trend <0.001 for both). Women who reached puberty later were at a greater odds of a higher Wolfe grade than women who had an earlier puberty (odds ratio associated with a 1 year delay in menarche 1.14, 95% CI: 1.01-1.27, adjusted for BMI and breast size at mammography). A higher BMI at any age during childhood or adult life was associated with a reduction in the odds of a higher Wolfe grade, after controlling for breast size and BMI at mammography, for example, standardised odds ratio for height at age 7 was 0.72 (95% CI: 0.64, 0.81). These findings reveal the importance of taking life-course changes in body size, and not just contemporaneous measures, into account when using mammographic density as an intermediate marker for risk of breast cancer.

Physical activity and risk of breast cancer in premenopausal women

Physical activity appears to be inversely related to risk of breast cancer, yet the results remain inconsistent. To evaluate this relation among premenopausal women and examine variation in risk according to level of obesity and use of oral contraceptives (OCs), the authors examined data from the Nurses' Health Study II. During 10 years of follow-up, 849 cases of invasive premenopausal breast cancer were confirmed. Physical activity was assessed by self-report at baseline and during follow-up using a validated questionnaire. Total physical activity was unrelated to risk of breast cancer. Women engaging in >or=27 metabolic equivalent (MET)-h week(-1) had a multivariate-adjusted relative risk (RR) of 1.04 (95% confidence interval (CI) 0.82-1.33) compared to those in the <3 MET-h week(-1) category. Among women with a BMI >or=30 kg m(-2), we observed a significant positive dose-response relation (P=0.04). Activity was unrelated to breast cancer risk at lower levels of BMI. A test for interaction between activity and BMI (<30, >or=30 kg m(-2)) was statistically significant (P=0.02). Among current OC users, higher activity was associated with a non-significantly lower risk of breast cancer (RR=0.59, 95% CI 0.30-1.16 for >or=27 vs <9 MET-h week(-1), P for linear trend=0.14). These results show no overall association between physical activity and risk of breast cancer among premenopausal women, but suggest that the effect of physical activity could be substantially modified by the underlying degree of adiposity. The potential interactions between physical activity, adiposity, and current use of OCs require further study.

Body mass index, serum sex hormones, and breast cancer risk in postmenopausal women

BACKGROUND

Obesity is associated with increased breast cancer risk among postmenopausal women. We examined whether this association could be explained by the relationship of body mass index (BMI) with serum sex hormone concentrations.

METHODS

We analyzed individual data from eight prospective studies of postmenopausal women. Data on BMI and prediagnostic estradiol levels were available for 624 case subjects and 1669 control subjects; data on the other sex hormones were available for fewer subjects. The relative risks (RRs) with 95% confidence intervals (CIs) of breast cancer associated with increasing BMI were estimated by conditional logistic regression on case-control sets, matched within each study for age and recruitment date, and adjusted for parity. All statistical tests were two-sided.

RESULTS

Breast cancer risk increased with increasing BMI (P(trend) =.002), and this increase in RR was substantially reduced by adjustment for serum estrogen concentrations. Adjusting for free estradiol reduced the RR for breast cancer associated with a 5 kg/m2 increase in BMI from 1.19 (95% CI = 1.05 to 1.34) to 1.02 (95% CI = 0.89 to 1.17). The increased risk was also substantially reduced after adjusting for other estrogens (total estradiol, non-sex hormone-binding globulin-bound estradiol, estrone, and estrone sulfate), and moderately reduced after adjusting for sex hormone-binding globulin, whereas adjustment for the androgens (androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and testosterone) had little effect on the excess risk.

CONCLUSION

The results are compatible with the hypothesis that the increase in breast cancer risk with increasing BMI among postmenopausal women is largely the result of the associated increase in estrogens, particularly bioavailable estradiol.

Effect of family history, obesity and exercise on breast cancer risk among postmenopausal women

We examined effects of obesity and lifetime exercise patterns on postmenopausal breast cancer risk according to family history in a large population-based case control study conducted in Los Angeles County, California, because we hypothesized that both factors would affect risk through similar mechanistic pathways, and that their effects would be stronger among women with a family history. We studied 1883 postmenopausal breast cancer case subjects and 1628 postmenopausal control subjects ranging in age from 55-72 years. Cases were diagnosed with incident breast cancer in the late 1980s and 1990s. Controls were individually matched to case subjects on age, ethnic origin and neighborhood. In-person interviews determined known breast cancer risk factors including: height, weight, lifetime exercise, and family history of breast and other cancers. Breast cancer risk was raised among women who had at least 1 first-degree relative with breast cancer (odds ratio [OR] = 1.68; 95% confidence interval [CI] = 1.36-2.08). Risk increased with increasing levels of body-mass index (wt-kg/ht-m(2)) (p-trend = 0.005). Breast cancer risk was reduced among women who maintained, on average, 17.6 metabolic equivalent of energy expenditure (MET)-hr of activity/week from menarche onward (OR = 0.66; 95% CI = 0.48-0.90). Body-mass index, adjusted for lifetime exercise, was strongly associated with breast cancer risk among women with a positive family history of breast cancer (p-trend < 0.0001), but only weakly associated among women with no family history (p-trend = 0.08; homogeneity of trends p = 0.0005). In contrast, the risk reduction associated with exercise activity, adjusting for body-mass index, was limited to women without a family history of breast cancer (p-trend = 0.001; homogeneity of trends p = 0.005). Body-mass index and exercise activity, both modifiable risk factors for breast cancer, seem to have differential effects depending on a woman's family history of breast cancer, and may impact risk through different biological mechanisms.

Central obesity and breast cancer risk: a systematic review

The specific effect of central rather than general obesity on breast cancer risk is not clear. This review examines the relationship between waist and waist-hip ratio (WHR) and risk of breast cancer in pre- and post-menopausal women using all available cohort and case-control data. The databases of the Cochrane Library, Medline, Cancer Lit and Embase were searched until October 2002. Relevant cohort and case-control studies with separate analyses in pre- and/or post-menopausal women were included. Random effects meta-analyses were carried out, subgrouped by pre- or post-menopausal status and cohort or case-control design. Sensitivity analyses were also performed. Five cohort studies with 72,1705 person years of observation (453 pre-menopausal and 2684 post-menopausal cases), and three case-control studies comprising 276 pre-menopausal cases with 758 pre-menopausal controls and 390 post-menopausal cases with 1071 post-menopausal controls were included. Pooled results from cohort studies using the most adjusted data [but without adjustment for weight or body mass index (BMI)] suggest a 39% lower risk of breast cancer in post-menopausal women with the smallest waist (compared with the largest) and a 24% lower risk in women with the smallest WHR. In pre-menopausal women, however, pooled results suggest that measurement of waist or WHR have little effect on risk of breast cancer. Adjustment for BMI abolished the relationship between waist or WHR and risk of post-menopausal breast cancer, but introduced such a relationship amongst pre-menopausal women. The relationship between a smaller measurement of waist or WHR and lower risk of post-menopausal breast cancer appears to result from the associated correlation with BMI. Amongst pre-menopausal women, central (not general) obesity may be specifically associated with an increased risk of breast cancer.

Leptin enhances, via AP-1, expression of aromatase in the MCF-7 cell line

Leptin, a product of adipocytes, is involved in the regulation of body weight and results strongly correlated to body fat content. An excess of fat mass represents a breast cancer risk factor particularly in postmenopausal women, where estrogen production by adipose tissue through its own aromatase activity stimulates tumor progression. Leptin stimulates estrogen production through the increase of aromatase expression and activity in human luteinized granulosa cells and adipose stromal cells. In the present study, we have examined the possible link that exists between leptin and breast cancer, focusing our attention on the direct effect of leptin on aromatase activity, which may enhance estrogen production and induce tumor cell growth stimulation. We have shown that leptin enhances aromatase mRNA expression, aromatase content, and its enzymatic activity in MCF-7. Aromatase expression appears to be regulated by tissue-specific promoter. It has been demonstrated that promoters II and 1.3 are the major promoters that drive aromatase expression in MCF-7. Transient transfection experiments using vector containing human aromatase promoters II and 1.3 sequence fused with luciferase reporter gene demonstrated that leptin is able to activate this promoter. In the presence of either mitogen-activated protein kinase inhibitor PD 98059 or ERK2 dominant negative as well as in the presence of STAT3 dominant negative, the stimulatory effects of leptin on aromatase promoter, enzymatic activity, and aromatase protein content were inhibited. Functional studies of mutagenesis and electrophoretic mobility shift assay revealed that the AP-1 motif is important in determining the up-regulatory effects induced by leptin on aromatase expression in MCF-7.

Obesity and height in urban Nigerian women with breast cancer

PURPOSE

To examine the relationship between obesity, height, and breast cancer in an urban Nigerian population.

METHODS

Between March 1998 and August 2000, we conducted a case-control study of hospital-based breast cancer patients (n = 234) and population-based controls (n = 273) using nurse interviewers in urban Southwestern Nigeria.

RESULTS

The study did not find a significant association between obesity (BMI >/= 30) and breast cancer among all women (OR = 1.51, 95% CI = 0.87-2.62) pre- (OR = 1.21, 95% CI = 0.56-2.60) and post-menopausal breast cancer patients (OR = 1.82, 95% CI = 0.78-4.31) in multivariate logistic regression analysis, while increasing height was positively associated with the risk of breast cancer among all women (OR = 1.05, 1.01 - 1.08), pre- (1.06, 1.01-1.10) and post-menopausal women (1.07, 1.01-1.13) for each cm. Age, irregular period, and early age of onset of periods were also found to be significantly associated with breast cancer risk.

CONCLUSION

This study failed to demonstrate an association between breast cancer risk and obesity while showing that height is positively associated with risk of breast cancer in urbanized Nigerian women.

Birth size in relation to age at menarche and adolescent body size: implications for breast cancer risk

Early age at menarche and tallness are associated with increased risk for breast cancer, and emerging evidence suggests that body size at birth also is positively associated with breast cancer risk in adulthood. We have explored whether this effect of birth size could be mediated by influencing age at menarche or body height during adolescence. Information on age at menarche and adolescent height among 3,343 Norwegian girls 13 to 19 years of age, born at term and whose mothers had no history of gestational disease was individually linked to information on birth weight and length recorded in the national Medical Birth Registry. We related quintiles of birth size, adjusted for length of gestation, to age at menarche and adolescent height and weight, using general linear modeling and Cox regression analyses. In a subsample of the population, we also had information on maternal age at menarche, as well as adult height and body mass index in both parents. We explored whether parental factors confounded the association between perinatal predictors and adolescent outcomes in the daughters. We found that age at menarche tended to occur earlier with decreasing birth weight (p for trend = 0.03), and girls who were thin at birth (i.e., in the lowest quintile of ponderal index) had an earlier age at menarche than other girls (p = 0.02). Weight and length at birth were strongly and positively related to tallness during adolescence (p for trend < 0.001), but ponderal index, indicating obesity at birth, was negatively associated with adolescent height (p for trend = 0.002). Adjustment for parental height, body mass index and maternal age at menarche, in the subsample where this information was available, indicated no substantial confounding by these parental factors. Our results suggest that a positive association between birth size and adult breast cancer is not likely to be mediated by early age at menarche, but possibly by increased body height in adolescence.

Exposures in childhood, adolescence and early adulthood and breast cancer risk: a systematic review of the literature

A growing body of work indicates that exposures over the life course have important roles to play in the aetiology of breast cancer. This review synthesises the literature that has been published in the area of early life events and female breast cancer risk. The review finds some evidence, primarily from cohort studies on the relationship between birthweight and breast cancer, to suggest that in utero events are related to breast cancer risk in adulthood. Strong evidence to support a positive association between height and breast cancer exists. Postulated mechanisms for this relationship include the role of early diet in subsequent disease risk, and the influence of endogenous growth factors mediating the relationship. There is some evidence to suggest that leg length is the component of height which is generating the observed associations between height and breast cancer. There is no consistent pattern of association between relative weight in childhood or adolescence and risk of breast cancer. The evidence to suggest an association between physical activity in early life and breast cancer risk is convincing from case-control studies, but is not fully substantiated by the results of three cohort studies. There are inconsistent results regarding the association between smoking at a young age and breast cancer risk. There is little evidence for an association between passive smoking in early life and breast cancer risk. No clear association between early drinking and breast cancer risk exists. These results are discussed in relation to possible underlying mechanisms and health promotion strategies which could reduce breast cancer risk.

Weight control and the management of obesity after menopause: the role of physical activity

BACKGROUND

Postmenopausal women have an increased tendency for gaining weight. The declines of endogenous estrogen, together with physical inactivity, are probably the major causes of this phenomenon. Postmenopausal overweight and obesity leads to increased rates of hypertension, diabetes mellitus, coronary artery disease, and all cause mortality. Additional consequences may include hormone-dependent cancer, gallstones, nephrolithiasis, and osteoarthritis. Weight loss can reverse many of these complications, reduce the number and dosages of medications used, and improve longevity. This difficult task requires lifestyle modification.

OBJECTIVES

To review the current information about the effects of physical activity on postmenopausal weight gain and its consequences and to provide basic strategies to treat obesity during the menopause transition.

METHODS

A Medline search together with a manual search of selected articles.

CONCLUSION

Several options for weight loss are available, yet lifestyle modification is essential in managing postmenopausal obesity and overweight. While this demands dietary and behavioral changes, a major element of this modification is regular physical activity, which reduces obesity-related morbidity and mortality. The amendment to a healthier lifestyle is achievable at the postmenopausal years. All medical personnel should advocate against overweight and obesity and provide tools for their management.

Fetal growth and subsequent risk of breast cancer: results from long term follow up of Swedish cohort

OBJECTIVE

To investigate whether size at birth and rate of fetal growth influence the risk of breast cancer in adulthood.

DESIGN

Cohort identified from detailed birth records, with 97% follow up.

SETTING

Uppsala Academic Hospital, Sweden.

PARTICIPANTS

5358 singleton females born during 1915-29, alive and traced to the 1960 census.

MAIN OUTCOME MEASURES

Incidence of breast cancer before (at age <50 years) and after (> or = 50 years) the menopause.

RESULTS

Size at birth was positively associated with rates of breast cancer in premenopausal women. In women who weighed > or =4000 g at birth rates of breast cancer were 3.5 times (95% confidence interval 1.3 to 9.3) those in women of similar gestational age who weighed <3000 g at birth. Rates in women in the top fifths of the distributions of birth length and head circumference were 3.4 (1.5 to 7.9) and 4.0 (1.6 to 10.0) times those in the lowest fifths (adjusted for gestational age). The effect of birth weight disappeared after adjustment for birth length or head circumference, whereas the effects of birth length and head circumference remained significant after adjustment for birth weight. For a given size at birth, gestational age was inversely associated with risk (P=0.03 for linear trend). Adjustment for markers of adult risk factors did not affect these findings. Birth size was not associated with rates of breast cancer in postmenopausal women.

CONCLUSIONS

Size at birth, particularly length and head circumference, is associated with risk of breast cancer in women aged <50 years. Fetal growth rate, as measured by birth size adjusted for gestational age, rather than size at birth may be the aetiologically relevant factor in premenopausal breast cancer.

A prospective study of adiposity and postmenopausal breast cancer risk: the Malmö Diet and Cancer Study

High BMI is a well-known risk factor for postmenopausal breast cancer. There have been some reports of excess risk in association with weight gain and WHR, but little is known about the influence of body fatness per se. Using data from the Malmö Diet and Cancer Study, a prospective cohort study, 12,159 postmenopausal women (59.9 +/- 7.7 years) were categorized by quintiles of baseline anthropometric and impedance measures and reported weight change since age 20. RRs from multivariate Cox regression models were calculated. All analyses were adjusted for age, height, smoking, alcohol consumption, occupation, marital status, parity, age at first pregnancy, age at menarche and current hormone use. During the 5.7 years of follow-up, there were 246 incident breast cancer cases. Weight, height, BMI and %BF were positively associated with risk of breast cancer (p(trend) <or= 0.02). %BF showed the strongest association, with an RR of 2.01 (95% CI 1.26-3.21) in the highest vs. lowest quintile. There was significant modification of this association by hormone use, suggesting a greater impact of body fatness among nonusers. Fat distribution was not independently associated with breast cancer risk. Women with weight gain >21 kg (top quintile) had an RR of 1.75 (95% CI 1.11-2.77) compared to women with low weight gain. Breast cancer risk in postmenopausal women is predicted by increased body fat and weight gain. %BF is a more discriminating risk factor for breast cancer incidence than the commonly used BMI.

Ethnicity-related variation in breast cancer risk factors

BACKGROUND

A variety of factors are predictors of breast cancer risk. However, the studies conducted to establish these risk factors have rarely included African American women. The few studies with sufficient numbers of African-American women suggest that risk factors for breast cancer among African-American women are similar to those of white women. Although risk factors may be similar for African-American and white women, differences in the prevalence of risk factors may explain the differences in patterns of incidence.

METHODS

The authors reviewed the epidemiologic studies of breast cancer among African-American women and identified resources with information regarding the prevalence of risk factors among African American and white women.

RESULTS

Considerable variation exists in the studies of breast cancer risk factors among African American women. Because few studies have included sufficient numbers of African-American women, no firm conclusions can be drawn regarding whether risk estimates for African American women differ from those of white women. Estimates of the prevalence of breast cancer risk factors indicate that African American and white women differ in terms of their ages at menarche, menstrual cycle patterns, birth rates, lactation histories, patterns of oral contraceptive use, levels of obesity, frequency of menopausal hormone use, physical activity patterns, and alcohol intake.

CONCLUSIONS

The risk factor profile of African-American women appears to differ from that of white women. This may explain in part, the higher incidence rates for African Americans before age 45 years and the lower incidence rates at older ages. Discussions of these data at a workshop highlighted the need for future research on breast cancer risk among African Americans. This research should acknowledge the heterogeneous heritage, cultural beliefs, and cultural knowledge of African-American women. Studies conducted in collaboration with the African-American community of women and with the breast cancer advocacy community can benefit from assistance in the design of questionnaires and recruitment of participants.

Environmental risk factors for breast cancer among African-American women

There are few unequivocably established environmental carcinogens for breast cancer in women. Nevertheless, environmental factors are believed to explain much of the international variation in breast cancer risk and possibly differences among racial/ethnic groups. Along with lifestyle, some adverse exposures may be higher in minority racial/ethnic groups and in underserved populations that experience higher ambient contamination. Associations have been found between environmental agents and breast cancer in subgroups of women who can be identified by common susceptibility traits as well as by timing of exposures at certain milestones of reproductive life. Susceptibility can be defined by social, environmental, and genetic modalities-factors that may predominate in certain racial/ethnic groups but that also transcend racial/ethnic boundaries. For example, genes involved in transcription and estrogen metabolism have rapid variants that are more prevalent among African-Americans, yet risk accompanying metabolic changes from these genes will prevail in all racial/ethnic groups. Lack of reliable exposure assessment remains a principal obstacle to elucidating the role of environmental exposures in breast cancer. Resources must be identified and consolidated that will enable scientists to improve exposure assessment and to assemble studies of sufficient size to address questions regarding exposure, susceptibility, and vulnerability factors in breast cancer. Breast cancer studies should be expanded to examine combinations of chemicals as well as competing or complementary exposures such as endogenous hormones, dietary intake, and behavioral factors.

Dietary fat and cancer

Based on current epidemiologic knowledge, public health recommendations to decrease total fat intake for the prevention of cancer appear largely unwarranted. Recommendations to decrease red meat intake, particularly processed meat or beef intake, may, on the other hand, decrease the risk of colorectal cancer and prostate cancer; it may have a beneficial effect on breast cancer as well, although the evidence is much less compelling in this regard. There appears to be no particular benefit regarding cancer prevention that would accrue from reducing fat intake from vegetable sources, and in the case of breast cancer, there is some suggestive but preliminary evidence that olive oil or other sources of monounsaturated fatty acids may modestly decrease risk. Overall, recommendations focused on controlling weight by regular physical activity and avoidance of excessive energy intake from all sources; increasing plant food intake; consuming a variety of whole grains, vegetables, and fruits; and decreasing red meat intake are likely to be more effective in decreasing risk of breast, colorectal, and prostate cancer than decreasing total fat intake. This conclusion is consistent with current recommendations for cancer prevention as promulgated by the American Cancer Society.

Overweight, obesity and fat distribution in 50- to 64-year-old participants in the European Prospective Investigation into Cancer and Nutrition (EPIC)

OBJECTIVE

To describe anthropometric characteristics of participants of the European Prospective Investigation into Cancer and Nutrition (EPIC).

DESIGN

A cross-sectional analysis of baseline data of a European prospective cohort study.

SUBJECTS

This analysis includes study populations from 25 centres in nine European countries. The British populations comprised both a population-based and a 'health-conscious' group. The analysis was restricted to 83 178 men and 163 851 women aged 50-64 years, this group being represented in all centres.

METHODS

Anthropometric examinations were undertaken by trained observers using standardised methods and included measurements of weight, height, and waist and hip circumferences. In the 'health-conscious' group (UK), anthropometric measures were predicted from self-reports.

RESULTS

Except in the 'health-conscious' group (UK) and in the French centres, mean body mass index (BMI) exceeded 25.0 kg m-2. The prevalence of obesity (BMI> or =30 kg m(-2)) varied from 8% to 40% in men, and from 5% to 53% in women, with high prevalences (>25%) in the centres from Spain, Greece, Ragusa and Naples (Italy) and the lowest prevalences (<10%) in the French centres and the 'health-conscious' group (UK). The prevalence of a large waist circumference or a high waist-to-hip ratio was high in centres from Spain, Greece, Ragusa and Naples (Italy) and among women from centres in Germany and Bilthoven (The Netherlands).

CONCLUSIONS

Anthropometric measures varied considerably within the EPIC population. These data provide a strong base for further investigation of anthropometric measures in relation to the risk of chronic diseases, especially cancer.

Body mass index in relation to ovarian cancer: a multi-centre nested case-control study

The incidence of ovarian cancer is up to 10 times higher in Western countries than in rural Asia and Africa. One common consequence of a Western lifestyle is the development of excessive body weight and obesity. A multi-centre prospective study was conducted to investigate the association between body mass index (BMI) and ovarian cancer risk. A case-control study was nested within 3 prospective cohorts in New York (USA), Umeå (Sweden) and Milan (Italy). Information on anthropometry, demographic characteristics, medical history and lifestyle was obtained at the time of subjects' recruitment in each cohort. Women diagnosed with primary, invasive epithelial ovarian cancer from the 3 cohorts (n = 122) diagnosed 12 months or later after recruitment into the respective cohort served as case subjects. For each case subject, 2 control subjects that matched the case subject on cohort, menopausal status, age and date of recruitment were randomly identified. Data were analyzed by conditional logistic regression. There was an inverse association between BMI and ovarian cancer risk. For increasing quartiles of BMI above the lowest, the ORs were 0.62 (0.32-1.21), 0.59 (0.30-1.17) and 0.46 (0.23-0.92), p = 0.03. Analyses limited to women diagnosed 3 or more years after recruitment into the cohorts did not alter these findings. When obese women (BMI > 30) were compared to lean women (BMI < or = 23), the inverse association became stronger, with an OR of 0.38 (0.17-0.85), p < 0.02. There was some evidence of direct association of ovarian cancer with height, which was limited to cancers diagnosed before age 55. Our data suggest that increasing body weight may confer a protection against ovarian cancer.

Childhood growth and adult cancer

Associations between different patterns of childhood growth and later adult health have recently received much attention. Most studies have found higher mortality in shorter people, explained by their higher incidence of cardiorespiratory disease. In this chapter, associations of cancer with markers of growth at different developmental phases - infancy, childhood and puberty - and with final adult height are reviewed. The relationship between birthweight and cancer is generally positive, with the greatest risk among high-birthweight babies. Childhood and adult tallness are related to higher cancer risk. This is particularly evident for cancers of the breast, prostate, colo-rectum, haematopoietic system and endometrium. Leg length may be more strongly associated than trunk length with cancer risk. Possible explanations for these findings are discussed in relation to nutritional intake and hormonal levels.

Breast cancer risk factors and age at diagnosis: an Icelandic cohort study

An increasing number of studies indicates that the strength and even direction of association between breast cancer and established risk factors differ according to the woman's age when she develops the disease. This was studied in the setting of a population based cancer registry using a databank with information on age at menarche, parity, age at first birth, oral contraceptive (OC) use, lactation, height and weight. From a cohort of 80.219 women attending population-based cervical and breast cancer screening in Iceland, 1120 cases were identified, aged 26-90 years at diagnosis and 10,537 controls, individually matched to the cases on birth year and age when attending. Information given at last visit before diagnosis was used in the analysis, applying conditional logistic regression. Odds ratios and statistical strength of relationships varied according to age at diagnosis for age at first birth, number of births, duration of lactation, height and weight. The decreased risk associated with young age at first birth and increasing duration of breast feeding became less pronounced with advancing age at diagnosis. A reduced risk associated with an increasing number of births was not detected in women diagnosed under the age of 40. An increased risk associated with giving first birth after 30 years of age was mainly detected in women who had only given 1 birth and were diagnosed under the age of 40 (OR = 7.06 95% CI = 2.16-23.01). A positive association with height and especially with weight was confined to women diagnosed after the age of 55. The results confirm that age at diagnosis should be taken into account when studying the effects of breast cancer risk factors.

The contribution of the environment (especially diet) to breast cancer risk

Environmental factors play an important role in breast carcinogenesis. Opportunities for prevention are limited, however, because most of the known or suspected risk factors are not targets for modification. Dietary factors have generally not emerged as crucial contributors to mammary tumor causation. We still appear to be missing a critical piece of the breast cancer puzzle because we can only explain a moderate proportion of international and national variation in breast cancer rates. Research needs to pursue new avenues, focusing on exposure windows that have not yet been sufficiently explored, such as events between conception and adolescence, and on modifiable risk factors that show large variation within or between populations.

Mediterranean diet and stroke: objectives and design of the SUN project. Seguimiento Universidad de Navarra

PURPOSE

The Mediterranean diet has been postulated as a protective factor against different diseases including stroke. Thus, an epidemiological study in a Mediterranean country, such as Spain, focused on diet may offer new insights of the potential benefits of this nutritional pattern to prevent the onset of cerebrovascular diseases.

METHODS

The SUN ("Seguimiento Universidad de Navarra") project is a prospective study among Spanish university alumni, aimed to identify the dietary determinants of stroke, coronary disease and other disorders. Two pilot studies have been developed. The first pilot study was focused on the understanding of the questionnaire. The second study used a random sample to assess the response proportion and the feasibility of using a mailing system for following-up the cohort. The first informative results are expected to be available after the first four years of following-up the cohort (2005). Here, we report the description of the baseline diet of the first participants in the cohort using data from 1,587 men and 2,260 women.

RESULTS

The outcome of our pilot studies ensure the feasibility of a mail-based cohort. In the baseline assessment, we found a high consumption of olive oil (18.5 g/person/day), red wine (28.8 g/person/day), legumes (102.5 g/person/day), vegetables (507.8 g/person/ day) and fruits (316.7 g/person/day), with a great between-subject variability. Also, the values for cereals (170.4g/person/day), dairy products (239.3 g/person/day) and meat and meat products consumption (186 g/person/ day) in this cohort were estimated. The coefficients of variation ranged in women from 56 (for vegetables) to 240% (for red wine) and in men from 62 to 180% (for these same two items), reflecting a wide heterogeneity in the diet of participants.

CONCLUSIONS

Although the participation was not high (22% according to the estimates of the pilot study), it was comparable to the proportion found in large previous cohorts such as the Nurses-II Health Study (24%). The sharp contrast in dietary habits between the US and Spain together with the high between-subjects variability we have found in our Spanish cohort provides an exceptional opportunity to assess the aspects of the Mediterranean diet, which may be protective against stroke and other neurological disorders.

Diet and environmental carcinogenesis in breast/gynaecological cancers

This paper reports on recent advances on the relation between diet, other environmental factors and breast and gynaecological cancers. Despite considerable research the issue remains still unsettled. The protective effect of a diet rich in vegetables and fruit, and thus selected (antioxidant) micronutrients, is not consistently reported in various studies. The possible relationship between fats and breast and female genital tract neoplasms also remains unconfirmed, while the potential benefits of physical activity remains unquantified. Alcohol appears to be related to the risk of breast cancer and overweight is associated with post-menopausal breast cancer and is strongly related to the risk of endometrial cancer.

Weight at birth and adolescence and premenopausal breast cancer risk in a low-risk population

We assessed breast cancer risk in relation to weight at birth and adolescence. In-person interviews were completed with the biological mothers of women aged 45 years and younger who participated in the Shanghai Breast Cancer Study in 1996-98 (288 cases, 350 controls). After adjustment for confounding, women who were 4000 g or more at birth were not at increased risk of breast cancer (odds ratio=0.7; 95% confidence interval 0.4-1.4) relative to women whose birth weight was 2500-2999 g. Compared with women of average perceived weight at age 15 years, no relation was apparent for heavier than average weight based on maternal report (odds ratio=0.7; 95% confidence interval 0.5-1.2) or self-report (odds ratio=1.0; 95% confidence interval 0.7-1.6). Perceived adolescent weight and height did not modify the association of birth weight with breast cancer risk. These results suggest that weight early in life is not related to premenopausal breast cancer risk in this low-risk population.

Dietary glycemic index and glycemic load, and breast cancer risk: a case-control study

BACKGROUND

Certain types of carbohydrates increase glucose and insulin levels to a greater extent than others. In turn, insulin may raise levels of insulin-like growth factors, which may influence breast cancer risk. We analyzed the effect of type and amount of carbohydrates on breast cancer risk, using the glycemic index and the glycemic load measures in a large case-control study conducted in Italy.

PATIENTS AND METHODS

Cases were 2,569 women with incident, histologically-confirmed breast cancer interviewed between 1991 and 1994. Controls were 2588 women admitted to the same hospital network for a variety of acute, non-neoplastic conditions. Average daily glycemic index and glycemic load were calculated from a validated 78-item food frequency questionnaire.

RESULTS

Direct associations with breast cancer risk emerged for glycemic index (odds ratio, OR for highest vs. lowest quintile = 1.4; P for trend <0.01) and glycemic load (OR = 1.3; P < 0.01). High glycemic index foods, such as white bread, increased the risk of breast cancer (OR = 1.3) while the intake of pasta, a medium glycemic index food, seemed to have no influence (OR = 1.0). Findings were consistent across different strata of menopausal status, alcohol intake, and physical activity level.

CONCLUSIONS

This study supports the hypothesis of moderate, direct associations between glycemic index or glycemic load and breast cancer risk and, consequently, a possible role of hyperinsulinemia/insulin resistance in breast cancer development.

Breast cancer epidemiology, prevention, and early detection

Breast cancer remains a worldwide public health concern despite the fact that mortality rates have been declining in some countries as a result of improvements in adjuvant therapy and screening for breast cancer. In the prevention arena, advances in our understanding of the effects of tamoxifen have led to the investigations of newer agents that may provide extended options for breast cancer prevention in high-risk women. For women who are carriers of a mutation in the breast cancer susceptibility genes BRCA1 or BRCA2, prophylactic oophorectomy and bilateral mastectomy have emerged as preventative surgical options that can significantly impact breast cancer risk. In addition, the identification of potentially modifiable risk factors for breast cancer such as dietary folate intake, alcohol consumption, physical activity, and certain anthropometric factors provides opportunities for intervening in breast cancer prevention both among women at average and high risk. The challenge remains in overcoming the limitations of mammography and clinical breast examination by developing and evaluating new technologies for breast cancer screening such as digital mammogram and breast magnetic resonance imaging.

Catechol-O-Methyltransferase (COMT) gene polymorphism and breast cancer risk in young women

Oestrogen exposure has long been considered to be a main risk factor of breast cancer. More recently, interest has also focused on the possible carcinogenic influence from oestrogen metabolites, such as catechol oestrogens. O-methylation, catalysed by Catechol-O-Methyltransferase (COMT), is one pathway by which the potentially carcinogenic catechol oestrogens can be inactivated. The gene coding for COMT protein contains a single-nucleotide polymorphism (SNP), resulting in an amino acid shift Val-->Met, which has been shown to determine high- and low-activity configuration of the enzyme. We hypothesized that the low-activity allele, COMT(Met), may be implicated in early onset breast cancer. In the present case-control study, including 126 young breast cancer patients (<or= 36 years) and 117 healthy female blood donors, we analysed the association between COMT(Met) genotype and risk of breast cancer. No significant difference in the frequency of low-/high-activity alleles was found between cases and controls, indicating that the polymorphism, as a single factor, may not contribute to breast carcinogenesis in young women.

Hormone replacement therapy use dramatically increases breast oestrogen receptor expression in obese postmenopausal women

BACKGROUND

It is known that use of hormone replacement therapy (HRT) by postmenopausal women increases the risk of breast cancer.

METHOD

In this study, oestrogen receptor (ER)-alpha expression is examined using standard immunoperoxidase technique.

RESULTS

Normal breast samples of 11 Australian postmenopausal women have been included in the ER-alpha study; the result showed a strong correlation (r(2) = 0.80) between ER-alpha expression in normal breast epithelial cells and body mass index (BMI) in normal women who currently use HRT.

CONCLUSION

This finding confirms that the possibility of increased risk of breast cancer associated with increased ER-alpha expression in normal breast epithelial cells, in turn associated with high BMI and the use of HRT.

Premorbid body weight and its relations to primary tumour diameter in breast cancer patients; its dependence on estrogen and progesteron receptor status

Hormonal mechanisms have been offered as an explanation for the higher frequency of large tumours, lymph node metastases and poorer prognosis in obese breast cancer patients than in lean ones. If hormonal mechanisms are important for these relations, they should probably act more strongly in patients with hormonal receptor positive tumours than in those with negative ones. We have examined if the relations between premorbid body weight or Quetelet's index (weight/height2) and tumour diameter are modified by estrogen receptor alpha (ER) and progesteron receptor (PgR) status. The analyses were based on 1,241 women with unilateral disease treated with modified radical mastectomy living in the geografic area of Haukeland Hospital. Their body weight and height have been measured as a mean 12.5 years before presentation of the disease. Body weight and Quetelet's index have been adjusted for age. The relations were studied using linear regression analyses adjusting the effect of body weight with height and mean nuclear area of the tumour cells and adjusting the effect of Quetelet's index for mean nuclear area. The main findings showed that patients with high body weight or Quetelet's index presented more often with PgR positive tumours than lean ones. Quetelet's index was also positively related to ER. These relations were present in patients older than 50 years of age (older). Patients with large tumours (>2.0 cm) had significantly higher body weight and Quetelet's index than those with small ones. These differences were significantly present in older patients and in patients with PgR negative and ER negative-PgR negative tumours. Linear regression analyses confirmed that tumour diameter increases with body weight and Quetelet's index. These relations were present in both lymph node groups and in older patients. Stratification according to hormonal receptor status showed these relations to be significant in patients with ER negative, with PgR negative and those with ER negative-PgR negative tumours only. Taking age and hormonal receptor status into consideration simultaneously, both body weight and Quetelet's index were significantly related to tumour diameter in older patients with hormone receptor negative tumours. In conclusion body size was positively related to hormone receptor status and to diameter of the primary tumour. The relation to tumour diameter was present in older patients with hormone receptor negative tumours. Although hormonal mechanisms able to act on the tumour can not be excluded, mechanisms acting independent of hormonal receptors must be considered. Different mechanisms related to body fat cytokines are discussed.

Review of anthropometric factors and breast cancer risk

Epidemiological evidence implicating anthropometric risk factors in breast cancer aetiology is accumulating. For premenopausal women, breast cancer risk increases with increasing height, but decreases with higher weight or body mass index, and no association with increased central adiposity exists. For postmenopausal women, an increased risk of breast cancer is found with increasing levels of all the anthropometric variables including height, weight, body mass index, waist-hip ratio, waist circumference and weight gain. Weight loss appears to decrease risk, particularly if it occurs later in life. Breast size may be a risk factor for breast cancer, however, the current evidence is inconclusive. Several hypothesized biologic mechanisms exist to explain how anthropometric factors influence breast cancer risk. Obesity may increase levels of circulating endogenous sex hormones, insulin and insulin-like growth factors that all, in turn, increase breast cancer risk. Genetic predisposition to obesity and to specific body fat distributions are also implicated. With obesity, there are increased levels of fat tissue that can store toxins and can serve as a continuous source of carcinogens. Recommendations for future research on anthropometric factors and breast cancer are provided. Sufficient evidence exists to support strategies to avoid weight gain throughout life as a means of reducing postmenopausal breast cancer risk.