Relation between obesity and breast cancer in young women

Body fatness at a young age, body fatness gain and risk of breast cancer: systematic review and meta-analysis of cohort studies

Higher body fatness in adulthood has been consistently associated with an increased risk of postmenopausal breast cancer, as well as a tendency towards a lower risk of premenopausal breast cancer. However, the association between body fatness at a young age (≤30 years), body fatness gain and the risk of breast cancer is less defined. PubMed and Web of Science databases were searched to identify relevant publications. Risk estimates with 95% confidence intervals from each study were transformed into a continuous variable for each 5 kg m^-2 increase in body mass index (BMI) and were pooled under a random-effects model. Each 5 kg m^-2 increase in BMI was significantly associated with a 14%, 12% and 17% lower risk of breast cancer later in life among all women, premenopausal women and postmenopausal women, respectively. Significant heterogeneity and publication bias were observed. The results remained unchanged after the trim and fill method was applied to correct the bias. Each 5 kg m^-2 increase in BMI from a young age until cohort entry was significantly associated with a 13% and 14% higher risk of breast cancer in all women and postmenopausal women, respectively. In summary, higher body fatness at a young age may have a protective role in the later development of breast cancer in both premenopausal and postmenopausal women. However, this potential benefit should not be overemphasized, as our findings suggest that increased body fatness gain from a young age is positively associated with postmenopausal breast cancer risk. These findings further justify the need to maintain a steady weight throughout life.

Body mass index, age at breast cancer diagnosis, and breast cancer subtype: a cross-sectional study

PURPOSE

Evidence suggests that premenopausal obesity decreases and postmenopausal obesity increases breast cancer risk. Because it is not well known whether this is subtype dependent, we studied the association between body mass index (BMI) and age at breast cancer diagnosis, or the probability of being diagnosed with a specific breast cancer phenotype, by menopausal status.

METHODS

All patients with non-metastatic operable breast cancer from the University Hospital Leuven diagnosed between January 1, 2000 and December 31, 2013 were included (n = 7020) in this cross-sectional study. Linear models and logistic regression were used for statistical analysis. Allowing correction for age-related BMI-increase, we used the age-adjusted BMI score which equals the difference between a patient's BMI score and the population-average BMI score corresponding to the patient's age category.

RESULTS

The quadratic relationship between the age-adjusted BMI and age at breast cancer diagnosis (p = 0.0207) interacted with menopausal status (p < 0.0001); increased age at breast cancer diagnosis was observed with above-average BMI scores in postmenopausal women, and with below-average BMI scores in premenopausal women. BMI was linearly related to the probabilities of Luminal B and HER2-like breast cancer phenotypes, but only in postmenopausal women. The relative changes in probabilities between both these subtypes mirrored each other.

CONCLUSION

BMI associates differently before and after menopause with age at breast cancer diagnosis and with the probability that breast cancer belongs to a certain phenotype. The opposite effect of increasing BMI on relative frequencies of Luminal B and HER2-like breast cancers suggests a common origin.

Obesity-associated Breast Cancer: Analysis of risk factors

Several studies show that a significantly stronger association is obvious between increased body mass index (BMI) and higher breast cancer incidence. Furthermore, obese women are at higher risk of all-cause and breast cancer specific mortality when compared to non-obese women with breast cancer. In this context, increased levels of estrogens due to excessive aromatization activity of the adipose tissue, overexpression of pro-inflammatory cytokines, insulin resistance, hyperactivation of insulin-like growth factors (IGFs) pathways, adipocyte-derived adipokines, hypercholesterolemia and excessive oxidative stress contribute to the development of breast cancer in obese women. While higher breast cancer risk with hormone replacement therapy is particularly evident among lean women, in postmenopausal women who are not taking exogenous hormones, general obesity is a significant predictor for breast cancer. Moreover, increased plasma cholesterol leads to accelerated tumor formation and exacerbates their aggressiveness. In contrast to postmenopausal women, premenopausal women with high BMI are inversely associated with breast cancer risk. Nevertheless, life-style of women for breast cancer risk is regulated by avoiding the overweight and a high-fat diet. Estrogen-plus-progestin hormone therapy users for more than 5 years have elevated risks of both invasive ductal and lobular breast cancer. Additionally, these cases are more commonly node-positive and have a higher cancer-related mortality. Collectively, in this chapter, the impacts of obesity-related estrogen, cholesterol, saturated fatty acid, leptin and adiponectin concentrations, aromatase activity, leptin and insulin resistance on breast cancer patients are evaluated. Obesity-related prognostic factors of breast cancer also are discussed at molecular basis.

Differential Patterns of Risk Factors for Early-Onset Breast Cancer by ER Status in African American Women

BACKGROUND

Given the disproportionately high incidence of early-onset breast cancer and aggressive subtypes, such as estrogen receptor (ER)-negative tumors, in African American (AA) women, elucidation of risk factors for early onset of specific subtypes of breast cancer is needed.

METHODS

We evaluated associations of reproductive, anthropometric, and other factors with incidence of invasive breast cancer by age at onset (<45, ≥45) in 57,708 AA women in the prospective Black Women's Health Study. From 1995 to 2013, we identified 529 invasive breast cancers among women <45 years of age (151 ER^-, 219 ER⁺) and 1,534 among women ≥45 years (385 ER^-, 804 ER⁺). We used multivariable Cox proportional hazards regression to estimate hazard ratios (HRs) for associations by age and ER status.

RESULTS

Higher parity, older age at first birth, never having breastfed, and abdominal adiposity were associated with increased risk of early-onset ER^- breast cancer: HRs were 1.71 for ≥3 births versus one birth; 2.29 for first birth after age 25 versus <20 years; 0.61 for ever having breastfed versus never; and 1.64 for highest versus lowest tertile of waist-to-hip ratio. These factors were not associated with ER^- cancer in older women or with ER⁺ cancer regardless of age.

CONCLUSIONS

Differences in risk factors by ER subtype were observed for breast cancer diagnosed before the age of 45 years.

IMPACT

Etiological heterogeneity by tumor subtype in early-onset breast cancer, in combination with a higher prevalence of the risk factors in AA women, may explain, in part, racial disparities in breast cancer incidence. Cancer Epidemiol Biomarkers Prev; 26(2); 270-7. ©2016 AACR.

Increased Incidence of Breast Cancer in Postmenopausal Women with High Body Mass Index at the Modena Screening Program

Purpose

We conducted a study to evaluate the relationship between body mass index (BMI) and the risk of breast cancer (BC) and outcome in a population of 14,684 women aged 55 to 69 years eligible to participate in the Mammography Screening Program (MSP) in the Province of Modena, Italy.

Methods

The study population was drawn from women who underwent mammography screening between 2004 and 2006 in the Province of Modena. Women were subdivided into obese, overweight, and normal-weight categories according to BMI and followed until July 31, 2010, to evaluate the BC incidence. The clinicopathological characteristics of BC were also evaluated in different groups of patients classified according to BMI. After BC diagnosis, patients were followed for a median period of 65 (range, 2–104) months. Second events (recurrences and second tumors) were recorded, and the 5-year event-free survival (EFS) was calculated.

Results

After a period of 73 months, 366 cases of BC were diagnosed. Compared with normal-weight women, obese women had a significantly higher incidence of BC (relative risk [RR], 1.32; p=0.040) (RR=1), larger tumors (27% of tumors were larger than T2 size), and more nodal involvement (38.5% of tumors were node-positive). Furthermore, a significantly higher rate of total events was seen in obese women compared with overweight and normal-weight patients, respectively (17.9% vs. 11.4% vs. 10.8%, p=0.032). The 5-year EFS was 89.0%, 89.0%, and 80.0% for normal-weight, overweight, and obese patients, respectively.

Conclusion

We observed a significantly higher risk of BC in obese women among those eligible to participate in the MSP in the Province of Modena. Finally, obese women had more second events and poorer EFS compared to nono bese women.

Body fatness throughout the life course and the incidence of premenopausal breast cancer

BACKGROUND

The role of body fatness in the aetiology of breast cancer is complex. We evaluated the independent and synergistic effects of body fatness, at different stages throughout a woman's life course, on premenopausal breast cancer risk.

METHODS

Premenopausal participants of the Nurses' Health Study II (NHSII) were followed from 1991 up to 2009. Body fatness factors including birthweight, somatotype (a 9-level pictogram with level 1 being the leanest) at ages 5 and 10 years and body mass index (BMI) at age 18 were collected at baseline. Current BMI was updated biennially. Multivariate Cox regression models were used to evaluate the association between each body fatness factor as well as cross-classification of all factors and the incidence of breast cancer.

RESULTS

Based on 1574 incident premenopausal breast cancer cases and 1 133 893 person-years of follow-up, a lower incidence was associated with lower birthweight: hazard ratio (HR) [95% confidence interval (CI)] = 0.74 (0.58-0.95) for <2.5kg vs 3.9+kg, P for trend < 0.001; higher somatotype at age 5: HR=0.57 (95% CI 0.44-0.73) for 5-9 vs 1, P fortrend < 0.0001]; and at age 10: HR=0.61 (95% CI 0.49-0.75) for 5-9 vs 1, P for trend < 0.0001]; and BMI at age 18: HR=0.67 (95% 0.47-0.95) for ≥ 27.5 kg/m² vs < 18.5 kg/m², P for trend = 0.009], after adjusting for age and body fatness measures earlier in life and other risk factors, respectively. No significant interaction between body fatness measures was found. Women with the lowest birthweight, the highest somatotype at ages 5 and 10 and the highest BMI at age 18 and currently had a 72% (95% CI 54%-83%) lower incidence of invasive premenopausal breast cancer than women with the opposite extreme of each body fatness indicator.

CONCLUSION

The lowest incidence of premenopausal breast cancer was associated with the lowest birthweight and the highest childhood, adolescent and early adult body fatness.

Cross-Sectional Associations between Body Size, Circulating Sex-Steroid Hormones and IGF Components among Healthy Chinese Women

The incidence of breast cancer has increased in Asian countries and rates of hormone receptor (HR) negative breast cancer exceed those of Western countries. Epidemiologic data suggest that the association between body size and BC risk may vary by HR status, and could differ geographically. While body size may influence BC risk by moderating the synthesis and metabolism of circulating sex-steroid hormones, insulin-like growth factor (IGF)-1 and related binding proteins, there is a dearth of literature among Asian women. We aimed to examine these specific associations in a sample of Chinese women. In Sichuan Province 143 women aged ≥40 years were recruited through outpatient services (2011–2012). Questionnaires, anthropometric measurements, and blood samples were utilized for data collection and linear regression was applied in data analyses. Among women <50 years we observed a non-monotonic positive association between body mass index (BMI) and 17β-estradiol, and a reversed J-shaped association between BMI and IGF-1 (p ≤0.05). We observed similar associations between waist-to-hip ratio and these markers. Our finding of augmented IGF-1 among women with low body mass may have implications for understanding breast tumor heterogeneity in diverse populations and should be evaluated in larger prospective studies with cancer outcomes.

Risk Factors for Premenopausal Breast Cancer in Bangladesh

Background. The incidence of premenopausal breast cancer is rising throughout South Asia. Our objective was to determine the role of risk factors associated with Westernization for premenopausal breast cancer in Bangladesh. Methods. We conducted a matched case-control study between January 1, 2007, and December 31, 2010, at four hospitals in Bangladesh. Cases were premenopausal women diagnosed with invasive breast cancer. Controls were premenopausal women with no personal history of breast cancer. Logistic regression was used to calculate the odds ratios (OR) for breast cancer. Results. We identified 129 age-matched pairs. The mean age of breast cancer diagnosis was 37.5 years. Each year decrease in the age of menarche significantly increased the risk of breast cancer (OR = 1.67, 95% CI 1.09–2.56, P = 0.02). The risk was also increased with a current body mass index of ≥25 kg/m² (OR = 5.24, 95% CI 1.10–24.9, P = 0.04). Age at first childbirth, parity, and breastfeeding were not significantly associated with premenopausal breast cancer risk (P > 0.05). Conclusions. Age at menarche and adult weight gain were associated with premenopausal breast cancer risk. Other factors associated with Westernization may not be relevant to premenopausal breast cancer risk in Bangladesh.

Metabolic syndrome is associated with increased breast cancer risk: a systematic review with meta-analysis

Background. Although individual metabolic risk factors are reported to be associated with breast cancer risk, controversy surrounds risk of breast cancer from metabolic syndrome (MS). We report the first systematic review and meta-analysis of the association between MS and breast cancer risk in all adult females. Methods. Studies were retrieved by searching four electronic reference databases [PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science, and ProQuest through June 30, 2012] and cross-referencing retrieved articles. Eligible for inclusion were longitudinal studies reporting associations between MS and breast cancer risk among females aged 18 years and older. Relative risks and 95% confidence intervals were calculated for each study and pooled using random-effects models. Publication bias was assessed quantitatively (Trim and Fill) and qualitatively (funnel plots). Heterogeneity was examined using Q and I² statistics. Results. Representing nine independent cohorts and 97,277 adult females, eight studies met the inclusion criteria. A modest, positive association was observed between MS and breast cancer risk (RR: 1.47, 95% CI, 1.15–1.87; z = 3.13; p = 0.002; Q = 26.28, p = 0.001; I² = 69.55%). No publication bias was observed. Conclusions. MS is associated with increased breast cancer risk in adult women.

Body mass index at early adulthood, subsequent weight change and cancer incidence and mortality

Obesity later in adulthood is associated with increased risks of many cancers. However, the effect of body fatness in early adulthood, and change in weight from early to later adulthood on cancer risk later in life is less clear. We used data from 13,901 people aged 45-64 in the Atherosclerosis Risk in Communities cohort who at baseline (1987-1989) self-reported their weight at the age of 25 and had weight and height measured. Incident cancers were identified through 2006 and cancer deaths were ascertained through 2009. Multivariable Cox proportional hazard models were used to relate body mass index (BMI) at age 25 and percent weight change from age 25 to baseline to cancer incidence and mortality. After adjusting for weight change from age 25 until baseline, a 5 kg/m(2) increment in BMI at age 25 was associated with a greater risk of incidence of all cancers in women [hazard ratio (95% confidence interval): 1.10 (1.02-1.20)], but not in men. Associations with incident endometrial cancer were strong [1.83 (1.47-2.26)]. After adjusting for BMI at age 25, a 5% increment in weight from age 25 to baseline was associated with a greater risk of incident postmenopausal breast cancer [1.05 (1.02-1.07)] and endometrial cancer [1.09 (1.04-1.14)] in women and incident colorectal cancer [1.05 (1.00-1.10)] in men. Excess weight during young adulthood and weight gain from young to older adulthood may be independently associated with subsequent cancer risk. Excess weight and weight gain in early adulthood should be avoided.

Computerized database management system for breast cancer patients

Data analysis based on breast cancer risk factors such as age, race, breastfeeding, hormone replacement therapy, family history, and obesity was conducted on breast cancer patients using a new enhanced computerized database management system. My Structural Query Language (MySQL) is selected as the application for database management system to store the patient data collected from hospitals in Malaysia. An automatic calculation tool is embedded in this system to assist the data analysis. The results are plotted automatically and a user-friendly graphical user interface is developed that can control the MySQL database. Case studies show breast cancer incidence rate is highest among Malay women, followed by Chinese and Indian. The peak age for breast cancer incidence is from 50 to 59 years old. Results suggest that the chance of developing breast cancer is increased in older women, and reduced with breastfeeding practice. The weight status might affect the breast cancer risk differently. Additional studies are needed to confirm these findings.

Higher incidence of premenopausal breast cancer in less developed countries; myth or truth?

Background

Fundamental etiologic differences have been suggested to cause earlier onset of breast cancer in less developed countries (LDCs) than in more developed countries (MDCs). We explored this hypothesis using world-wide breast cancer incidence data.

Methods

We compared international age-standardized incidence rates (ASR) of pre- (<50 years) and postmenopausal (≥50 years) breast cancers as well as temporal trends in ASRs of pre-and postmenopausal breast cancer among selected countries during 1975–2008. We used joinpoint log-linear regression analysis to estimate annual percent changes (APC) for premenopausal and postmenopausal breast cancer in the northern Europe and in Black and White women population in the US.

Results

Premenopausal breast cancers comprised a substantially higher proportion of all incident breast cancers in LDCs (average 47.3%) compared to MDCs (average 18.5%). However, the ASR of premenopausal breast cancer was consistently higher in MDCs (29.4/100,000) than LDCs (12.8/100,000). The ASR of postmenopausal cancer was about five-fold higher in the MDCs (307.6/100,000) than the LDCs (65.4/100,000). The APC of breast cancer in Denmark was substantially higher in postmenopausal (1.33%) than premenopausal cancer (0.98%). Higher incidence of breast cancer among the white than black women in the US was pertained only to the postmenopausal cancer.

Conclusion

The substantial and consistent lower age-specific incidence of breast cancer in LDCs than in MDCs contradicts the theory of earlier onset. Demographic differences with fewer old women in LDCs and lower prevalence of risk factors of postmenopausal cancer are the most likely explanation to the lower mean age at diagnosis in these countries.

Benign Breast Diseases and Body Mass Index: Is There a Correlation?

Breast cancer is the leading cancer affecting women in America. Body mass index (BMI) is a known risk factor for the development of breast cancer. The relationship of BMI to benign breast disease is less clear. In addition, certain benign pathologies are associated with an increased risk of cancer. We sought to measure the incidence of benign pathologies and to correlate these findings with BMI and age. All patients undergoing breast biopsy at our center from 2000 to 2005 were identified (n = 1717). Age, BMI, family history, sex, and diagnosis were determined. Patients were grouped into BMI, age, and intervention groups. χ2 ( P < 0.05) was used to identify statistical significance. Fibrocystic disease and fibroadenoma were seen with a lower incidence for patients older than 55 years of age, whereas pathologies requiring further surgical intervention were seen in higher proportions in patients older than 55 years of age. All pathologies were noted to decrease with increasing BMI, except for fibroadenoma, which peaked in BMI group 25 to 29.9 kg/m2. The presence of benign pathologies was associated with age as expected. Interestingly, although BMI is associated with increased risk of breast cancer, increasing BMI was not associated with benign pathologies that are associated with increased risk of breast cancer. Further study of this area is warranted.

Biochemical and molecular mechanisms for the association between obesity, chronic inflammation, and breast cancer

Upper body obesity is a risk factor for postmenopausal breast cancer and is related to an aggressive tumor phenotype and a poor prognosis regardless of menopausal status. After the menopause, the major mechanism for the association with disease risk is elevated estrogen production by adipose tissue, due to a high level of aromatase activity: these hormone-dependent tumors express both estrogen and progesterone receptors. Other important biological factors of risk include leptin and adiponectin, adipokines with opposing endocrine and paracrine activities, and obesity-related hyperinsulinemia. Chronic inflammation of the breast adipose tissue, which occurs in some obese women and is indicated by the accumulation of macrophages around dead adipocytes ("crown-like structures"), rather than adiposity per se, may prove to be the pathological lesion responsible for both local aromatase induction, and enhanced invasiveness and metastatic capacity through biological mechanisms that involve leptin, tumor necrosis factor-α, and insulin. A causal association between obesity in premenopausal women and breast cell epithelial-mesenchymal transition, perhaps with the participation of the Wnt signaling pathway, and aggressive hormone-independent breast cancer is suggested by a number of experimental and clinical studies.

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.

The association between 25-hydroxyvitamin D and mammographic density in healthy pre- and postmenopausal women regardless of the menstrual cycle phase: a cross-sectional study

Vitamin D deficiency is a known risk factor of breast cancer. An association between vitamin D and breast density has been suggested; however, it remains controversial. The aim of this study was to determine the association between serum 25-hydroxyvitamin D [25(OH)D] level and mammographic density. Subjects in our study included 517 patients who visited the health promotion center of the University Hospital. Mammographic density was classified using the American College of Radiology, Breast Imaging Reporting and Data System. Analysis of variance was performed to clarify the association of serum 25(OH)D level and mammographic density, and odds ratio was calculated by ordinal logistic regression analysis. The mean serum 25(OH)D level was 14.3 ± 7.0 ng/mL in all subjects. In correlation analysis, weak negative correlation was observed between serum 25(OH)D level and mammographic density groups (r = -0.09, P = 0.049). However, ordinal logistic regression analysis showed no statistically significant association between serum 25(OH)D level and mammographic density (odds ratio: 0.75, 95% confidence interval: 0.50-1.13). Results of our study showed that there is no significant association between serum 25(OH)D level and mammographic density. It is thought to be an another mechanism of serum 25(OH)D level on breast cancer risk in addition to breast density.

Simplifying the energy balance message for breast cancer prevention

Simple prevention messages based on understandable biologic principles are likely to be adopted. The long-held premise that postmenopausal obesity elevates, but premenopausal obesity reduces, risk for breast cancer is confusing to the public. Furthermore, decades of positive energy balance may be difficult to suddenly reverse at the time of the menopause. In this issue (beginning on page 583), Cecchini et al. suggest that obesity may also be a risk factor for pre-menopausal women 35 and older who have additional risk factors for breast cancer. Although the relative impact of dysregulated energy metabolism depends on many factors including age, hormonal milieu, and competing risk factors, as well as how it is measured, avoiding weight gain after age 30 is increasingly being recognized as a simple way to reduce risk of breast cancer.

Age of 40 years or younger is an independent risk factor for locoregional failure in early breast cancer: a single-institutional analysis in saudi arabia

Background. This study was undertaken to evaluate the impact of prognostic factors on the locoregional failure-free survival of early breast cancer patients. Methods. In this single-institutional study, 213 breast cancer patients were retrospectively analysed. Fifty-five of 213 patients were ≤40 years of age at diagnosis. The impact of patient- or treatment-related factors on the locoregional failure-free survival was assessed using the Kaplan-Meier method. The simultaneous impact of factors on the locoregional failure-free survival was assessed using the Cox proportional hazards regression analysis. Results. The median follow-up time of the censored patients was 22 months (mean 28 months, range 3-92 months). On univariate analysis, statistically significant factors for the locoregional failure-free survival were the age (≤40 versus >40 years), T stage (Tis, T0-2 versus T3-4), molecular tumor type (luminal A versus luminal B, Her2neu overexpression, or triple negative), and lymphovascular status (LV0 versus LV1). On multivariate analysis, age and T stage remained statistically significant. Conclusions. Being 40 years or younger has a statistically significant independent adverse impact on the locoregional failure-free survival of patients with early breast cancer.

Body mass index and the risk for developing invasive breast cancer among high-risk women in NSABP P-1 and STAR breast cancer prevention trials

High body mass index (BMI) has been associated with an increased risk for breast cancer among postmenopausal women. However, the relationship between BMI and breast cancer risk in premenopausal women has remained unclear. Data from two large prevention trials conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP) were used to explore the relationship between baseline BMI and breast cancer risk. The analyses included 12,243 participants with 253 invasive breast cancer events from the Breast Cancer Prevention Trial (P-1) and 19,488 participants with 557 events from the Study of Tamoxifen and Raloxifene (STAR). Both studies enrolled high-risk women (Gail score ≥ 1.66) with no breast cancer history. Women in P-1 were pre- and postmenopausal, whereas women in STAR (P-2) were all postmenopausal at entry. Using Cox proportional hazards regression, we found slight but nonsignificant increased risks of invasive breast cancer among overweight and obese postmenopausal participants in STAR and P-1. Among premenopausal participants, an increased risk of invasive breast cancer was significantly associated with higher BMI (P = 0.01). Compared with BMI less than 25, adjusted HRs for premenopausal women were 1.59 for BMI 25 to 29.9 and 1.70 for BMI 30 or more. Our investigation among annually screened, high-risk participants in randomized, breast cancer chemoprevention trials showed that higher levels of BMI were significantly associated with increased breast cancer risk in premenopausal women older than 35 years, but not postmenopausal women.

Association between body mass index and risk of breast cancer in Tunisian women

BACKGROUND AND OBJECTIVES

The number of breast cancer in women has increased dramatically in Tunisia. The cause is perceived to stem from adaptation to a westernized life style which increases body mass index (BMI). This study aimed to investigate the association between BMI and breast cancer among Tunisian women.

DESIGN AND SETTING

Hospital-based case control study of breast cancer patients seen between November 2006 and April 2009 at the University College Hospital Farhat Hached in Sousse, Tunisia.

PATIENTS AND METHODS

Standardized questionnaires concerning BMI and other anthropometric data were completed on 400 breast cancer cases and 400 controls. The controls were frequency-matched to the cases by age.

RESULTS

BMI at diagnosis was positively correlated with the risk of breast cancer among postmenopausal women (P<.001 for trend). When compared with women with a low BMI (<19), women with a BMI of 23-27 and 27-31 had a 1.7-fold (95% CI, 1.1-2.9) and 2.1-fold (95% CI, 1.1-3.9) increased risk of breast cancer, respectively, after adjustment for non-anthropometric risk factors. BMI at diagnosis was not related to the risk of breast cancer among premenopausal women. The odds ratios for premenopausal women with a BMI of 23-27 and 27-31 were 1.5 (95% CI, 0.8-2.8) and 1.3 (95% CI, 0.4-4.5), respectively. Furthermore, present BMI was not associated with breast cancer risk in either pre- and postmenopausal women.

CONCLUSIONS

Weight control in obese women may be an effective measure of breast cancer prevention in postmenopausal women.

A review of body size and breast cancer risk in Hispanic and African American women

Obesity is an epidemic in the United States, especially among Hispanics and African Americans. Studies of obesity and breast cancer risk have been conducted primarily in non-Hispanic whites. There have been few studies of the association between body mass index (BMI) or weight gain and the risk of breast cancer in minorities, and the results have been inconsistent. Because most studies are conducted primarily in non-Hispanic whites, the etiology of breast cancer in minorities is not well understood. The authors of the current report reviewed the literature on the association between obesity, weight, and weight gain and breast cancer in minorities using a combination of the Medical Subject Heading (MeSH) terms "obesity," "body mass index," "weight," "weight gain," "Hispanic," and "African American." Only publications in English and with both risk estimates and 95% confidence intervals were considered. Forty-five studies of body size and breast cancer risk in non-Hispanic whites were identified. After an exhaustive search of the literature, only 3 studies of body size and breast cancer were conducted in Hispanic women were identified, and only 8 such studies in African American women were identified. The results were inconsistent in both race/ethnicity groups, with studies reporting positive, inverse, and null results. Thus, as obesity rates among Hispanics and African Americans continue to rise, there is an urgent need to identify the roles that both obesity and adult weight gain play in the development of breast cancer in these minorities. Additional studies are needed to provide more understanding of the etiology of this disease and to explain some of the disparities in incidence and mortality.

Postmenopausal obesity promotes tumor angiogenesis and breast cancer progression in mice

Obese postmenopausal women have a 50% higher risk of breast cancer than non-obese women. There is not an animal model that mimics postmenopausal obesity related to breast cancer progression. Using age-relevant C57BL/6 mice, this study determined whether postmenopausal obesity increases VEGF expression, tumor angiogenesis, and breast tumor growth. Ovariectomy (OVX) was performed in 12 sixty week-old female mice, then followed by a low-fat (5%, LF, n=6) or a high-fat (60%, HF, n=6) diet for 12 weeks. In the eighth week of the dietary program, 10(6) E0771 (mouse breast cancer) cells were injected in the left fourth mammary gland. Tumor size was monitored for 4 weeks. Body weights were monitored weekly. At the end of the experiment, blood samples, visceral fat and tumors were collected for measuring VEGF expression using ELISA and intratumoral microvessel density (IMD) using CD31 immunochemistry. Body weight was significantly increased in OVX/HF mice, compared to OVX/LF group (55.3±1.7 vs. 41.5±1.5 g; p < 0.01). There was a two-fold increase in the ratio of visceral fat/BW in OVX/HF mice, compared to those in OVX/LF group (0.062±0.005 vs. 0.032±0.003; p < 0.01). Postmenopausal obesity significantly increased breast tumor weight over the control (4.62±0.63 vs. 1.98±0.27 g; p < 0.01) and IMD (173±3.7 vs. 139±4.3 IM#/mm^2; p < 0.01). Tumor VEGF levels were higher in OVX/HF mice, compared to OVX/LF group (73.3±3.8 vs. 49.5±4.3 pg/mg protein; p < 0.01). Plasma VEGF levels (69±7.1 vs. 48±3.5 pg/ml) and visceral fat VEGF levels (424.4±39.5 vs. 208.5±22.4 pg/mg protein) were significantly increased in OVX/HF mice, compared to OVX/LF group, respectively (n=6; p < 0.01). Interestingly, adipose tissue primary culture showed that subcutaneous fat released more VEGF, compared to visceral fat (6.77±1.14 vs. 0.94±0.16 pg/mg tissue; n=6; p < 0.01). These findings support the hypothesis that postmenopausal obesity promotes tumor angiogenesis and breast cancer progression, possibly through increased adipose tissue mass and adipokines such as VEGF that could systemically and locally affect breast cancer progression.

Adult weight change and incidence of premenopausal breast cancer

Overweight and obesity are inversely related to the risk of breast cancer among premenopausal women. We assessed the association between adult weight change since age 18 years with the risk of breast cancer among premenopausal women to explore whether weight gain was associated with a decrease in risk and weight loss was associated with an increase in risk. A total of 56,223 premenopausal participants in the Nurses' Health Study and 109,385 premenopausal participants in the Nurses' Health Study II were prospectively followed for up to 32 years and 18 years, respectively, and weight change since age 18 years was assessed biennially. The incidence of invasive breast cancer was assessed throughout follow-up. Weight loss of 5 kg or more since age 18, maintained for at least 4 years, was related to lower incidence of premenopausal breast cancer, compared to maintaining a stable weight, but this relation was of borderline statistical significance (covariate-adjusted HR = 0.75; 95% CI 0.52-1.09). Weight gain since age 18 years was also inversely related to breast cancer incidence among premenopausal women (covariate-adjusted p for trend = 0.01), but the association weakened after controlling for weight at age 18 and did not reach statistical significance (p for trend = 0.08). Although obesity and breast cancer among premenopausal women are inversely related, weight loss since age 18 years did not increase and weight gain did not significantly decrease the risk of premenopausal breast cancer among participants in the large prospective cohorts of NHS and NHS II.

Associations of breast cancer risk factors with tumor subtypes: a pooled analysis from the Breast Cancer Association Consortium studies

BACKGROUND

Previous studies have suggested that breast cancer risk factors are associated with estrogen receptor (ER) and progesterone receptor (PR) expression status of the tumors.

METHODS

We pooled tumor marker and epidemiological risk factor data from 35,568 invasive breast cancer case patients from 34 studies participating in the Breast Cancer Association Consortium. Logistic regression models were used in case-case analyses to estimate associations between epidemiological risk factors and tumor subtypes, and case-control analyses to estimate associations between epidemiological risk factors and the risk of developing specific tumor subtypes in 12 population-based studies. All statistical tests were two-sided.

RESULTS

In case-case analyses, of the epidemiological risk factors examined, early age at menarche (≤12 years) was less frequent in case patients with PR(-) than PR(+) tumors (P = .001). Nulliparity (P = 3 × 10(-6)) and increasing age at first birth (P = 2 × 10(-9)) were less frequent in ER(-) than in ER(+) tumors. Obesity (body mass index [BMI] ≥ 30 kg/m(2)) in younger women (≤50 years) was more frequent in ER(-)/PR(-) than in ER(+)/PR(+) tumors (P = 1 × 10(-7)), whereas obesity in older women (>50 years) was less frequent in PR(-) than in PR(+) tumors (P = 6 × 10(-4)). The triple-negative (ER(-)/PR(-)/HER2(-)) or core basal phenotype (CBP; triple-negative and cytokeratins [CK]5/6(+) and/or epidermal growth factor receptor [EGFR](+)) accounted for much of the heterogeneity in parity-related variables and BMI in younger women. Case-control analyses showed that nulliparity, increasing age at first birth, and obesity in younger women showed the expected associations with the risk of ER(+) or PR(+) tumors but not triple-negative (nulliparity vs parity, odds ratio [OR] = 0.94, 95% confidence interval [CI] = 0.75 to 1.19, P = .61; 5-year increase in age at first full-term birth, OR = 0.95, 95% CI = 0.86 to 1.05, P = .34; obesity in younger women, OR = 1.36, 95% CI = 0.95 to 1.94, P = .09) or CBP tumors.

CONCLUSIONS

This study shows that reproductive factors and BMI are most clearly associated with hormone receptor-positive tumors and suggest that triple-negative or CBP tumors may have distinct etiology.

Risk factors for breast cancer among young women in southern Iran

Age standardized incidence rates of breast cancer in developed countries is nearly threefold higher than in developing countries. Iran has had one of the lowest incidence rates for breast cancer in the world, but during the last four decades increasing incidence rates of breast cancer made it the most prevalent cancer in Iranian women. After adjustment for age, Iranian young women are at relatively higher risk of breast cancer than their counterparts in developed countries. The purpose of this study was to investigate some established risk factors of breast cancer in Iranian young women. A hospital-based case control study comprising 521 women with histologically confirmed, incident breast cancer and 521 controls frequency-matched by age and province of residence was conducted. Logistic regression performed to investigate associations of reproductive and anthropometric factors with breast cancer risk. In multivariate analysis, family history [odds ratio (OR): 1.61; 95% confidence interval (CI): 1.07-2.42], oral contraceptives (OC) usage (OR: 1.52; 95% CI: 1.11-2.08), low parity (OR parity ≥ 3 vs. 1-2: 0.33; 95% CI: 0.23-0.49), employment (OR: 1.83; 95% CI: 1.05-3.23) and shorter period of breast feeding (OR ≥ 37 months vs. < 37: 0.61; 95% CI: 0.44-0.84) were related to a higher risk of breast cancer in young women. This was the first study focusing on risk factors of breast cancer in Iranian young women. The trend of decreasing parity and shortened duration of breast feeding along with OC usage might partly explain the rapid rising of breast cancer incidence in Iranian young women.

Effects of high-isoflavone soy diet vs. casein protein diet and obesity on DMBA-induced mammary tumor development

Obesity and elevated serum insulin growth factor-1 (IGF-1) level are major risk factors in the development of breast cancer. We investigated the long-term effects of high-isoflavone soy intake and obesity on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumor development and on serum IGF-1 and binding protein (IGFBP-3) levels. Lean and obese female Zucker rats fed casein or high-isoflavone soy protein were orally gavaged at age 50 days with DMBA and sacrificed after 147 days. The majority of lean casein-fed rats (69%) developed mammary tumors compared to 50% in lean soy-fed rats (P=0.176). In the obese groups, 76% of soy-fed rats developed mammary tumors compared to 15% of obese casein-fed rats (P<0.001). At age 43 days, IGFBP-3 was increased in the lean soy-fed rats compared to the lean casein-fed rats (P<0.05). At age 99 days, soy- and obese casein-fed rats exhibited increased serum IGF-1 compared to the lean rats and this increase was maintained for the rest of the experiment (P<0.05). Obese rats fed casein exhibited increased IGFBP-3 levels (P<0.001). However, obese rats fed soy exhibited a significant decrease in IGFBP-3 levels compared to the lean soy-fed rats (P<0.001) and a significant decrease in IGFBP-3 levels compared to the obese casein-fed rats (P<0.001). At age 197 days, IGFBP-3 levels were increased in obese casein-and soy-fed rats (P<0.001). The results suggest that female Zucker rats fed casein diets are protected against DMBA-induced mammary tumors, which is not the case for those on high-isoflavone soy diet, and changes in the concentration of serum IGFBP-3 may contribute to the incidence of DMBA-induced mammary tumors.

Poor early growth and excessive adult calorie intake independently and additively affect mitogenic signaling and increase mammary tumor susceptibility

We previously showed that offspring of rat dams receiving a protein-restricted (low protein) diet throughout pregnancy and lactation develop mammary tumors more quickly. Rapid post-weaning mammary growth and mammary tissue overexpression of insulin receptor, insulin-like growth factor-1 receptor (IGF-1R), estrogen receptor isoform alpha and v-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (ERBB2), correlated with this risk. The objectives of this study were therefore (i) to identify underlying mechanisms of increased risk through candidate and global approaches; (ii) to determine if excessive calorie intake further increased risk and if so, (iii) to identify the molecular mechanisms mediating this. We provide evidence for transcriptional upregulation of IGF-1R by Sp1 in LP mammary tissue (P < 0.01). Cell cycle control and DNA damage repair gene cyclin-dependent kinase inhibitor 1A (CDKN1A) (p21waf1) was also upregulated (P < 0.05) as was transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cell (P < 0.05) and adhesion gene CDH1 (P < 0.05). Invasion and metastasis markers matrix metalloproteinase 9 and serpin peptidase inhibitor, clade E, member 1 (SERPIN1) were upregulated (both P < 0.05), whereas metastasis suppressor gene NME1 was downregulated (P < 0.01). Feeding a highly palatable diet (HPD) to increase calorie intake from puberty, additively and independently increased early mammary tumor risk, which correlated with increased serum insulin and triglyceride concentrations (P < 0.05). PTEN gene expression was reduced both by early protein restriction (P < 0.05) and HPD (P < 0.01), which may induce Akt in cell survival pathways. Progesterone receptor and ERBB2 (both P < 0.05) expression increased as an effect of an interaction between maternal diet and adult nutrition, with subsequent downstream activation of the mitogen-activated protein kinase pathway. We conclude that poor early growth and excessive calorie intake exert independent and additive effects on mitogenic growth factor signaling to influence mammary tumor susceptibility.

Oxidant/antioxidant status, lipids and hormonal profile in overweight women with breast cancer

This study was carried out to determine the relationships between leptin concentrations, lipid alterations, oxidant/ antioxidant status, in vitro LDL oxidizability and LDL-fatty acid composition in overweight breast cancer patients. Glucose, insulin, leptin, lipids, LDL-cholesteryl ester fatty acids, markers of oxidant status (MDA, Hydroperoxides, carbonyl proteins, conjugated dienes) and markers of antioxidant status (vitamins A, C, E, erythrocyte activities of the enzymes superoxide dismutase, SOD, catalase, glutathione peroxidase,GPx, and glutathione reductase, GR and the serum total antioxidant status, ORAC) were investigated in breast cancer patients and in control women. Our findings showed that insulin, leptin, triglyceride, cholesterol and LDL-C concentrations were increased in patients compared to controls. ORAC and vitamin C and E values were lower while plasma hydroperoxide, carbonyl protein and conjugated diene levels, SOD and GPx activities were higher than in controls. Alterations in LDL-fatty acid composition were associated with their enhanced oxidative susceptibility. There were significant positive correlations between leptin concentrations and LDL-C, hydroperoxides, carbonyl proteins, SOD activity, baseline conjugated diene levels and oxidation rate, and significant negative correlations between leptin and ORAC, lag time and LDL-PUFA in patients. In conclusion, breast cancer is associated with lipid alterations and enhanced oxidative stress linked to high leptin levels in overweight.

Obesity, hyperinsulinemia and breast cancer: novel targets and a novel role for metformin

The relationship between obesity, metabolic syndrome, diabetes and cancer has been recognized for many years. Multiple studies conducted in the last 20 years have identified molecular mechanisms responsible for this phenomenon. Elucidation of the important role of insulin, IGF receptor, mTOR and AMP-activated protein kinase in breast cancer biology has led to the development and subsequent clinical evaluation of novel targeted therapies, including IGF-1 receptor-specific antibodies or tyrosine kinase inhibitors and inhibitors of mTOR. There is also a growing interest in the use of metformin, which has been shown to possess antitumor activity resulting from activation of AMP-activated protein kinase and subsequent inhibiton of mTOR, as well as from decreased circulating insulin levels. Metformin has been shown to inhibit proliferation, invasion and angiogenesis of neoplastic cells and to overcome resistance of breast cancer to chemotherapy, hormonal therapy and HER2 inhibition. Recently, metformin has been demonstrated to inhibit breast cancer stem cell growth and to synergize with chemotherapy in suppression of tumor growth and prolongation of survival of breast tumor-bearing animals. Several currently ongoing Phase II and III clinical studies are evaluating the therapeutic efficacy of metformin in the treatment of early and advanced breast cancer patients.

Interaction between menopausal status and obesity in affecting breast cancer risk

Obesity has a complex relationship to breast cancer risk that differs in premenopausal and postmenopausal women. Before the menopause, the level of adiposity is inversely related to risk, indicative of a protective effect, whereas in postmenopausal women, particularly the elderly, the association is a positive one, consistent with obesity being a risk factor. The importance of high estrogen production in adipose tissue, with consequent elevation of circulating biologically available estradiol, in the promotional effect of obesity on postmenopausal breast carcinogenesis is well established; the resulting tumors express both estrogen and progesterone receptors. The mechanism(s) for the protective effect in premenopausal women is less well understood, but the breast cancers that do develop in the presence of obesity are most often estrogen and progesterone receptor negative, consistent with the selection of non-estrogen-dependent tumor cells which are dependent on growth factors such as insulin, insulin-like growth factor-I and some adipokines. The influence of menopausal status on the relationships between adiposity and breast cancer appears to be modified within each category by age; the protective effect before the menopause may be limited to younger women (<35 years), and the adverse effect was found to apply specifically to older postmenopausal women. Although randomized trials of weight reduction for postmenopausal breast cancer prevention have not been performed, observational studies suggested that risk reduction does occur; in addition, other health benefits of weight control need to be considered regardless of menopausal status.

Obesity, body fat distribution and breast cancer

Abstract Strong epidemiological data exists implicating anthropometric risk factors in breast cancer aetiology. In premenopausal women the risk of breast cancer increases with increased height, yet decreases with increasing weight and BMI. Although the evidence is not strong, a counter-intuitive positive relationship between central adiposity and premenopausal breast cancer risk is emerging. In post-menopausal women an increased risk in breast cancer has been found for all anthropometric measures: height, weight, BMI, measures of central adiposity (waist:hip ratio and waist circumference) and weight gain, with breast size being a possible additional risk factor. Weight loss as a strategy for reducing breast cancer risk seems to offer a viable prophylaxis in obese post-menopausal women, although data are limited. The evidence for anthropometric measures in relation to breast cancer risk is consistently stronger for post-menopausal women compared with premenopausal women and seems to be dependent on age. A number of possible biological mechanisms have been offered to explain the link between breast cancer risk and anthropometric measures. It has been hypothesised that obesity, especially central fat deposits, linked to insulin resistance, increases circulating hormones such as oestrogens, androgens, insulin, insulin-like growth factor-1 (IGF-1), and decreased levels of hormone-binding proteins such as steroid hormone-binding globulin and IGF-1 binding protein-1. Thus there are resulting increased concentrations of bioavailable sex hormones, which have been linked to increased breast cancer risk. As obesity is an important modifiable risk factor, which has been linked to increased post-menopausal breast cancer, public health recommendations to maintain ideal weight throughout life are warranted.

Minireview: Obesity and breast cancer: the estrogen connection

There is now substantial evidence that overweight and/or obesity and/or weight gain are risk factors for the development of postmenopausal breast cancer. In addition, obesity and/or elevated body mass index at breast cancer diagnosis has a negative impact on prognosis for both premenopausal and postmenopausal women. Therefore, understanding the mechanism of how obesity affects the mammary tumorigenesis process is an important health issue. Elevated serum estrogen levels as well as enhanced local production of estrogen have been considered primary mediators of how increased body weight promotes breast cancer development in postmenopausal women. Here, we provide an overview of estrogen's relationship with both obesity and breast cancer as separate entities. Human and relevant preclinical studies are cited. In addition, other growth factors that may be involved in this relationship are considered.

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.

Adiposity, the metabolic syndrome, and breast cancer in African-American and white American women

Breast cancer, the second most common cause of cancer-related deaths in American women, varies substantially in incidence and mortality according to race and ethnicity in the United States. Although the overall incidence of breast cancer among African-American (AA) women is lower than in white American women, this cancer is more common in young premenopausal AA women, and AA breast cancer patients of all ages are more likely to have advanced disease at diagnosis, higher risk of recurrence, and poorer overall prognosis. Epidemiological studies indicate that these differences may be attributable in part to variation in obesity and body fat distribution. Additionally, AA women more frequently exhibit breast cancer with an aggressive and metastatic phenotype that may also be attributable to the endocrine and metabolic changes associated with upper body obesity. These changes include both elevated estrogen and androgen bioactivity, hyperinsulinemia, and perturbations of the adipokines. Type 2 diabetes and the metabolic syndrome, which are more common in AA women, have also been associated with breast cancer risk. Moreover, each of the individual components of the syndrome has been associated with increased breast cancer risk, including low levels of the adipocytokine, adiponectin. This review explores the specific roles of obesity, body fat distribution (particularly visceral and sc adipose tissue), type 2 diabetes, metabolic syndrome, and adipocytokines in explaining the differential patterns of breast cancer risk and prognosis between AA and white American women.

Obesity and prognosis of breast cancer

Obesity has a complicated relationship to both breast cancer risk and the clinical behaviour of the established disease. It is suggested that obesity is associated with both an increased risk of developing breast cancer risk and worse prognosis after disease onset. In post-menopausal women, various measures of obesity such as body mass index, weight, weight gain and waist : hip ratio have all been positively associated with risk of developing breast cancer. In most but not all case-control and prospective cohort studies, an inverse relationship has been found between weight and breast cancer among pre-menopausal women. Some data suggest that adult weight gain and central obesity increase the risk of pre-menopausal breast cancer. Obesity at the time of diagnosis is thought to be significant as a poor prognostic factor. Obesity is associated with adverse outcomes in both pre- and post-menopausal women with breast cancer. Many cancer survivors seek ways to minimize the risk of recurrence and death because of breast cancer. Despite complex and at times controversial data, enough evidence is available at present to suggest that weight management should be a part of the strategy to prevent the occurrence, recurrence and death because of breast cancer. In this review the effect of obesity on the prognosis of breast cancer is examined in detail.

Obesity: its influence on breast cancer susceptibility

Obesity is an increasing worldwide epidemic. With an increased prevalence of obesity there is an increase in obesity-related cancers, such as breast cancer. Although reproductive and lifestyle choices are among the best-recognized risk factors for breast cancer, few of these can be modified readily by the individual. Obesity is unlike these other risk factors since it can be modified and controlled. Breast cancer prognosis is worse in patients who are obese, and epidemiological data suggests that obesity is a significant risk factor for postmenopausal breast cancer. Addressing the obesity epidemic, at both an individual and public health level, is expected to have a significant impact on breast cancer incidence and mortality.

Role of Lipid Peroxidation in the Epidemiology and Prevention of Breast Cancer

We have recently proposed a common mechanistic pathway by which obesity and hypertension lead to increased renal cell cancer risk. Our hypothesis posits lipid peroxidation, which is a principal mechanism in rodent renal carcinogenesis, as an intermediate step that leads to a final common pathway shared by numerous observed risks (including obesity, hypertension, smoking, oophorectomy/hysterectomy, parity, preeclampsia, diabetes, and analgesics) or protective factors (including oral contraceptive use and alcohol) for renal cell cancer [Cancer Causes Control 2002;13:287-93]. During this exercise, we have noticed how certain risk factors for renal cell carcinoma are protective for breast cancer and how certain protective factors for renal cell carcinoma increase risk for breast cancer. Parity and oophorectomy, for example, are positively associated with renal cell carcinoma but are negatively associated with breast cancer. Similarly, obesity and hypertension are positively associated with renal cell carcinoma, but obesity is negatively associated with breast cancer in premenopausal women and hypertension during pregnancy is negatively associated with breast cancer. Furthermore, alcohol intake, negatively associated with renal cell carcinoma, is also positively associated with breast cancer. We propose here the possibility that lipid peroxidation may represent a protective mechanism in breast cancer. Although this runs counter to the conventional view that lipid peroxidation is a process that is harmful and carcinogenic, we present here the chemical and biological rationale, based on epidemiologic and biochemical data, which may deserve further consideration and investigation.

A case-control study evaluating the association of purposeful physical activity, body fat distribution, and steroid hormones on premenopausal breast cancer risk

The objective of this case-control study was to investigate the relationship between purposeful physical activity, body fat distribution, body mass index, and steroid hormones. These factors are known to be implicated in modulating breast cancer risk in premenopausal women. A total of 112 newly diagnosed, premenopausal breast cancer patients and 106 age-matched premenopausal disease-free controls were admitted to the study. Information regarding personal, medical, hormonal, and reproductive history, smoking and alcohol use, physical activity history, and anthropometric measurements was obtained. Serum samples for steroid hormone assays were collected and analyzed. Disease-free premenopausal controls had a significantly higher physical activity index (PAI) (p</=0.05), however, significantly higher weight (p</=0.05), body mass index (BMI) (p=0.01), waist (p</=0.005) and hip (p</=0.05) circumferences, waist:hip ratios (p</=0.05), and serum total estradiol levels (p<0.0005) were observed in cancer cases. The final model using stepwise logistic regression analysis indicates that the variables that significantly predicted breast cancer risk were waist:hip ratio (odds ratio [OR]=1.11, p</=0.005) and serum total estradiol levels (OR=1.03, p</=0.0001). Our study provides some evidence that purposeful physical activity may reduce upper body fat distribution associated with adult weight gain. This may be a result of alterations in the steroid hormone pathway, such as reduced estradiol levels. This demonstrates the potential mechanism through which increased physical activity can reduce the risk for breast cancer in premenopausal women.

Long-term weight change and breast cancer risk: the European prospective investigation into cancer and nutrition (EPIC)

We examined prospectively the association between weight change during adulthood and breast cancer risk, using data on 1358 incident cases that developed during 5.8 years of follow-up among 40 429 premenopausal and 57 923 postmenopausal women from six European countries, taking part in the European prospective investigation into cancer and nutrition study. Multivariate Cox regression models were used to calculate hazard ratios according to weight change (kg), defined as the weight difference between age at enrolment and age 20 adjusted for other risk factors. Changes in weight were not associated with premenopausal breast cancer risk. In postmenopausal women, weight gain was positively associated with breast cancer risk only among noncurrent hormone replacement therapy (HRT) users (P-trend ⩽0.0002). Compared to women with a stable weight (±2 kg), the relative risk for women who gained 15–20 kg was 1.50 (95% confidence interval (CI) 1.06–2.13). The pooled RR per weight gain increment of 5 kg was 1.08 (95% CI 1.04–1.12). Weight gain was not associated with breast cancer risk in current HRT users, although, overall, these women experienced a much higher risk of breast cancer compared with nonusers. Our findings suggest that large adult weight gain was a significant predictor of breast cancer in postmenopausal women not taking exogenous hormones.

Anthropometric factors and the risk of premenopausal breast cancer in Germany

Studies have shown fairly consistent results regarding an inverse relationship between overweight and premenopausal breast cancer risk, but reported effects of weight changes have been inconsistent. Data was analysed on weight, weight changes, height and body build for 558 premenopausal women with breast cancer and 1116 controls below 51 years who participated in a population-based case-control study in Germany from 1992 to 1995. Larger body build at menarche conferred a protective effect, when compared with smaller build [odds ratio (OR) 0.69, 95% confidence interval (CI) 0.49, 0.96]. In comparison with the lowest quartile, higher quartiles of weight gain from the lowest adult weight to current weight conferred a significant protective effect to those who attained their lowest adult weight after but not before the (median) age of 21, with OR and 95% CI of 0.52 (0.32, 0.83), 0.50 (0.30, 0.81), 0.56 (0.34, 0.94) for second, third and fourth quartiles respectively. Our findings are consistent with studies that found weight gain to be protective against premenopausal breast cancer and suggest that this effect may be more pronounced for women who were lean in adolescence and early adulthood.

Association Between Body Mass Index and Risk of Formation of Breast Cancer in Chinese Women

OBJECTIVE

To analyse the association between body mass index (BMI) and breast cancer risk among Chinese women in Hong Kong.

METHODS

We conducted a population-based case control study of breast cancer in June 2002. Standardized questionnaires concerning BMI and other anthropometric data were completed by patients at the Queen Mary Hospital (QMH). The cases were 198 women aged 24-85 years who had documented breast cancer in 1995-2000 by triple assessment criteria, and the controls were 353 women who were followed up at QMH for benign breast disease after breast cancer had been excluded by triple assessment. The controls were frequency-matched to the cases by age.

RESULTS

BMI at diagnosis was positively correlated with the risk of breast cancer among postmenopausal women (p < 0.001 for trend). Also, when compared with women with a low BMI (< 19), women with a BMI of 23-27 and 27-31 had a 1.73-fold (95% confidence interval, CI, 1.04-2.86) and 2.06-fold (95% CI, 1.08-3.93) increased risk of breast cancer, respectively, after adjustment for non-anthropometric risk factors. BMI at diagnosis, however, was not related to the risk of breast cancer among premenopausal women. The odds ratios for premenopausal women with a BMI of 23-27 and 27-31 were 1.5 (95% CI, 0.82-2.71) and 1.32 (95% CI, 0.39-4.43), respectively. Furthermore, present BMI and BMI 5 years before diagnosis were poorly associated with breast cancer risk among both pre- and postmenopausal women.

CONCLUSION

Weight control in obese women may be an effective measure for breast cancer prevention in postmenopausal women.

A Prospective Study of Body Size in Different Periods of Life and Risk of Premenopausal Breast Cancer

The prevalence of obesity at all ages is increasing epidemically worldwide. Information on the association between premenopausal breast cancer and body size during childhood and teenage years is scarce. In 1991 to 1992, a prospective cohort study was assembled in Norway and Sweden. We included in the analysis presented here 99,717 premenopausal women. During the follow-up period, which ended in December 1999, 733 of these women developed a primary invasive breast cancer. Overweight and obesity [body mass index (BMI) &gt; 25 kg/m2] at enrolment was associated with a decreased risk of premenopausal breast cancer (P for linear trend = 0.007). Apparent associations between perceived body shape at age 7 and BMI at age 18, with heavier builds at both ages seemingly being protective for premenopausal breast cancer risk, lost their statistical significance after adjustment for BMI at cohort enrolment. Body size at age 7 was correlated with BMI at age 18 (r = 0.43); BMI at age 18 was correlated with adult BMI (r = 0.48). Changes in body size from age 7 or 18 to adulthood did not affect per se risk of premenopausal breast cancer risk. Height was related to risk, with a statistically significantly 30% reduced risk only in women shorter than 160 cm as compared with taller ones. The decreased risk of premenopausal breast cancer was observed in overweight and obese women without, but not in those with, a family history of breast cancer.

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.

Can the Gail model be useful in American Indian and Alaska Native populations?

BACKGROUND

Very little is known about breast carcinoma risk factors for American Indian/Alaska Native (AI/AN) women undergoing screening. The Gail model has been a useful tool for predicting the risk of breast carcinoma in several populations. It has not been applied systematically to AI/AN women.

METHODS

The current study was a retrospective review of 1458 screening mammograms performed for AI/AN women. The authors applied the Gail model to estimate both absolute risk and relative risk for breast carcinoma for AI/AN women screened in South Dakota, Arizona, and Alaska.

RESULTS

The mean age of the women was 52.4 years. The onset of menses was not significantly different than expected. The average age at first birth was 20 years, very few women were nulliparous, and few women were age > 30 years at first live birth. The proportion of women reporting a first- or second-degree relative with breast carcinoma was similar to the proportion in the general population. The results of the model indicated an overall average relative risk that ranged from 1.42 to 2.69 compared with white American women, depending on the model assumptions used. Using a modified Gail model and calculating an imputed absolute risk, the expected incidence of breast carcinoma in this population increased to rates of 170-180 per 100,000 in the next 10 years, a significant increase over the Surveillance, Epidemiology and End Results-derived incidence rates from 1988 to 1992 of 31.6 per 100,000 for AI women in New Mexico and 78.9 per 100,000 for AN women.

CONCLUSIONS

The model indicated a likelihood of increasing rates of breast carcinoma in the study population. The data obtained were useful in generating preliminary estimates of breast carcinoma risk in the study population, for which no prospective population survey has been completed. The inherent weaknesses in the current retrospective study indicated the need for a large-scale prospective data collection to confirm these exploratory findings.

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.