Risk of breast cancer in relation to anthropometry, blood pressure, blood lipids and glucose metabolism: a prospective study within the Malmö Preventive Project

Serum cholesterol and the risk of developing hormonally driven cancers: A narrative review

Although cholesterol has been hypothesized to promote cancer development through several potential pathways, its role in the risk of developing hormonally driven cancer is controversial. This literature review summarizes evidence from the highest quality studies to examine the consistency and strength of the relationship between serum cholesterol parameters and incidence of hormonally driven cancer. Articles were identified using EMBASE. Longitudinal observational studies published between January 2000 and December 2020 were considered for inclusion. The endpoint of interest was incident prostate, ovary, breast, endometrium, and uterine cancers. In total, 2732 reports were identified and screened; 41 studies were included in the review. No associations were found for ovarian cancer. Most endometrial cancer studies were null. The majority (76.9%) of studies reported no association between cholesterol and prostate cancer. Data on breast cancer were conflicting, associations limited, and effect sizes modest. Our results do not provide evidence for a clear association between cholesterol and different types of incident, hormonally driven reproductive cancers. Future studies should investigate the impact of lipid-lowering therapy.

Effect of Serum Lipid Profile on the Risk of Breast Cancer: Systematic Review and Meta-Analysis of 1,628,871 Women

Dyslipidemia has been linked to breast cancer incidence. The aim of the present meta-analysis was to further investigate the relationship between the serum lipid profile and breast cancer risk. Databases such as PubMed, EMBASE, and Web of Sciences were searched up to the end of January 2021 using certain MeSH and non-MeSH keywords and combinations to extract related published articles. Twenty-six prospective studies involving 1,628,871 women, of whom 36,590 were diagnosed with breast cancer during the follow-up period met the inclusion criteria. A negative and significant association was found between the HDL-C level and the risk of breast cancer (relative risk (RR): 0.85, 95% CI: 0.72–0.99, I²: 67.6%, p = 0.04). In contrast, TG (RR: 1.02, 95% CI: 0.91–1.13, I²: 54.2%, p = 0.79), total cholesterol (TC) (RR: 0.98, 95% CI: 0.90–1.06, I²: 67.2%, p = 0.57), apolipoprotein A (ApoA) (RR: 0.96, 95% CI: 0.70–1.30, I²: 83.5%, p = 0.78) and LDL-C (RR: 0.93, 95% CI: 0.79–1.09, I²: 0%, p = 0.386) were not associated with breast cancer development. In studies adjusting for hormone use and physical activity, breast cancer risk was positively correlated with TC (RR: 1.05, 95% CI: 1.01–1.10). Similarly, TG was significantly related to breast cancer development after adjustment for baseline lipids (RR: 0.92, 95% CI: 0.85–0.99) and race (any races mentioned in each study) (RR: 1.80, 95% CI: 1.22–2.65). In the present meta-analysis, HDL-C was inversely related to breast cancer risk. Overall, data on the links between lipids and breast cancer are conflicting. However, there is increasing evidence that low HDL-C is related to an increased risk for this type of malignancy.

A review of menopause nomenclature

Menopause nomenclature varies in the scholarly literature making synthesis and interpretation of research findings difficult. Therefore, the present study aimed to review and discuss critical developments in menopause nomenclature; determine the level of heterogeneity amongst menopause definitions and compare them with the Stages of Reproductive Aging Workshop criteria. Definitions/criteria used to characterise premenopausal and postmenopausal status were extracted from 210 studies and 128 of these studies were included in the final analyses. The main findings were that 39.84% of included studies were consistent with STRAW classification of premenopause, whereas 70.31% were consistent with STRAW classification of postmenopause. Surprisingly, major inconsistencies relating to premenopause definition were due to a total lack of reporting of any definitions/criteria for premenopause (39.84% of studies). In contrast, only 20.31% did not report definitions/criteria for postmenopause. The present findings indicate that there is a significant amount of heterogeneity associated with the definition of premenopause, compared with postmenopause. We propose three key suggestions/recommendations, which can be distilled from these findings. Firstly, premenopause should be transparently operationalised and reported. Secondly, as a minimum requirement, regular menstruation should be defined as the number of menstrual cycles in a period of at least 3 months. Finally, the utility of introducing normative age-ranges as supplementary criterion for defining stages of reproductive ageing should be considered. The use of consistent terminology in research will enhance our capacity to compare results from different studies and more effectively investigate issues related to women's health and ageing.

Metabolic syndrome and breast cancer: a dangerous association for postmenopausal women

BACKGROUND

Breast cancer(BC) is the most common cancer in women worldwide, the relationship between metabolic syndrome(MetS) and BC needs to be better clarified. Today the early diagnosis of breast cancer(BC) is yet a challenging problem in clinical practice, so the evidence that a well identified population of postmenopausal women, affected by MetS, presents a high risk, of breast cancer occurrence, is useful for breast cancer prevention. Our study aims to assess the prevalence of metabolic syndrome, diagnosed according to current guidelines, in postmenopausal women with breast cancer, and its role as an independent risk factor.

RESULTS

MetS rate was significantly higher among women affected by BC:10.1%, 33 women, than CG:5.4%, 18 women, Chi-squared4.8,Odds ratio1.94,c.i.95%,p<0.02. Metabolic cardiomyopathy rate was significantly higher among women affected by BC:5.8%, 18 women, than CG:1.8%, 6 women, Chi-squared6.5,Odds ratio3.2,c.i.95%,p<0.01. Otherwise MetS rate without cardiomyopathy was higher among women affected by BC:4.8%, 15 women, than CG:3.4%, 11 women, but in a not statistically significant way, Chi-squared0.8,Odds ratio1.35,c.i.95%,p<0.36.

CONCLUSION

There was a significant relationship, in our population, between MetS and BC, adding evidence to this controversial association, the relationship was even tighter, when restricted to women affected by metabolic cardiomyopathy; otherwise it, restricted to women affected by MetS, without metabolic cardiomyopathy, was not statistically significant. Since the prevalence of MetS is increasing worldwide, just like the incidence of BC, an intervention is needed to improve physical activity and weight reduction to decrease the MetS rate.

High-sensitivity C-reactive protein, hemoglobin A1c and breast cancer risk: a nested case-control study from Alberta's Tomorrow Project cohort

PURPOSE

Our aim is to examine the associations between high-sensitivity C-reactive protein (hsCRP) and hemoglobin A1c (HbA1c), common biomarkers of inflammation and insulin resistance, respectively, with breast cancer risk, while adjusting for measures of excess body size.

METHODS

We conducted a nested case-control study within the Alberta's Tomorrow Project cohort (Alberta, Canada) including 197 incident breast cancer cases and 394 matched controls. The sample population included both pre- and postmenopausal women. Serum concentrations of hsCRP and HbA1c were measured from blood samples collected at baseline, along with anthropometric measurements, general health and lifestyle data. Conditional logistic regression was used to evaluate associations between hsCRP, HbA1c, and breast cancer risk adjusted for excess body size (body fat percentage) and other risk factors for breast cancer.

RESULTS

Higher concentrations of hsCRP were associated with elevated breast cancer risk (odds ratio [OR] 1.27; 95% confidence interval [95% CI] 1.03-1.55). The observed associations were unchanged with adjustment for body fat percentage. Higher HbA1c concentrations were not significantly associated with an increased breast cancer risk (OR 1.22; 95% CI 0.17-8.75).

CONCLUSION

These data suggest that hsCRP may be associated with elevated breast cancer risk, independent of excess body size. However, elevated concentrations of HbA1c did not appear to increase breast cancer risk in apparently healthy women.

Investigation of the association between metabolic syndrome and breast cancer patients

One of the most serious cancers among women is breast cancer. This disease is the first reason for the death of women due to cancer. Increasing breast cancer risk may associate with many factors including genetic, reproductive factors, people's lifestyle, metabolic syndrome (MS) and hormones. MS has been known as a risk factor for prostate, pancreatic, breast and colorectal cancers. The purpose of this review is to identify the relationship between MS components and breast cancer individually. This study was performed by researching electronic database references including PubMed, Google Scholar, CINAHL ProQuest, and web of science through 2019. The effect of MS with its components and breast cancer was reported in many studies. Nevertheless, a thorough understanding of the mechanisms involved remains a challenge. However, one can take several preventive measures, including a proper diet, which is one of the most important determinants of metabolic status. Also, general preventive recommendations are including reducing alcohol consumption, red meat and total fat in the diet. Moreover, increasing the consumption of vegetable and fruit reduce the proportion of MS patients to improve the outcome of breast cancer patients.

Relationship Between Metabolic Syndrome and Postmenopausal Breast Cancer

INTRODUCTION

Metabolic syndrome is associated with an increased risk of diabetes mellitus (DM) and coronary heart disease. It may also be associated with a higher risk of some common cancers. The objective of this study was to determine the relationship between metabolic syndrome and breast cancer in postmenopausal women.

METHODS

We present a prospective cohort study of postmenopausal women. This cohort was divided into two groups: the «benign diagnosis group», including women who were studied after breast cancer screening; and the «malignant tumor group», including patients with breast cancer that had been diagnosed by biopsy. Age, weight, height, body mass index (BMI), abdominal perimeter, serum glucose, LDL, HDL and insulin levels were analyzed as variables under study. The HOMA-IR homeostatic model formula was used to assess insulin resistance. The differences were considered statistically significant when P<.05.

RESULTS

Two hundred women with a mean age of 61.5±9.6 (range: 37-93) were enrolled in the study, consisting of 150 (75%) patients with a benign diagnosis and 50 (25%) patients with a malignant tumor. BMI and abdominal perimeter were higher in the group with a malignant tumor (P<.05). The incidence of DM and metabolic syndrome was higher in the malignant tumor group (P<.005). In the malignant tumor group, much higher incidences correlated with fasting glycemic levels >100mg/dL, insulin levels >10mIU/L and HOMA-IR scores >2.7 (P<.05).

CONCLUSIONS

There is a relationship between metabolic syndrome and postmenopausal breast cancer. More studies are needed to establish methods for the prevention of breast cancer in women with metabolic syndrome.

Fat mass changes during menopause: a metaanalysis

OBJECTIVE

Data: Fat mass has been shown to increase in aging women; however, the extent to which menopausal status mediates these changes remains unclear. The purpose of this review was to determine (1) how fat mass differs in quantity and distribution between premenopausal and postmenopausal women, (2) whether and how age and/or menopausal status moderates any observed differences, and (3) which type of fat mass measure is best suited to the detection of differences in fat mass between groups.

STUDY

This review with metaanalyses is reported according to Metaanalysis of Observational Studies in Epidemiology guidelines.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies (published up to May 2018) were identified via PubMed to provide fat mass measures in premenopausal and postmenopausal women. We included 201 cross-sectional studies in the metaanalysis, which provided a combined sample size of 1,049,919 individuals and consisted of 478,734 premenopausal women and 571,185 postmenopausal women. Eleven longitudinal studies were included in the metaanalyses, which provided a combined sample size of 2472 women who were premenopausal at baseline and postmenopausal at follow up.

RESULTS

The main findings of this review were that fat mass significantly increased between premenopausal and postmenopausal women across most measures, which included body mass index (1.14 kg/m²; 95% confidence interval, 0.95-1.32 kg/m²), bodyweight (1 kg; 95% confidence interval, 0.44-1.57 kg), body fat percentage (2.88%; 95% confidence interval, 2.13-3.63%), waist circumference (4.63 cm; 95% confidence interval, 3.90-5.35 cm), hip circumference (2.01 cm; 95% confidence interval, 1.36-2.65 cm), waist-hip ratio (0.04; 95% confidence interval, 0.03-0.05), visceral fat (26.90 cm²; 95% confidence interval, 13.12-40.68), and trunk fat percentage (5.49%; 95% confidence interval, 3.91-7.06 cm²). The exception was total leg fat percentage, which significantly decreased (-3.19%; 95% confidence interval, -5.98 to -0.41%). No interactive effects were observed between menopausal status and age across all fat mass measures.

CONCLUSION

The change in fat mass quantity between premenopausal and postmenopausal women was attributable predominantly to increasing age; menopause had no significant additional influence. However, the decrease in total leg fat percentage and increase in measures of central fat are indicative of a possible change in fat mass distribution after menopause. These changes are likely to, at least in part, be due to hormonal shifts that occur during midlife when women have a higher androgen (ie, testosterone) to estradiol ratio after menopause, which has been linked to enhanced central adiposity deposition. Evidently, these findings suggest attention should be paid to the accumulation of central fat after menopause, whereas increases in total fat mass should be monitored consistently across the lifespan.

World Cancer Research Fund International: Continuous Update Project-systematic literature review and meta-analysis of observational cohort studies on physical activity, sedentary behavior, adiposity, and weight change and breast cancer risk

PURPOSE

The purpose of the present study was to systematically review the complex associations between energy balance-related factors and breast cancer risk, for which previous evidence has suggested different associations in the life course of women and by hormone receptor (HR) status of the tumor.

METHODS

Relevant publications on adulthood physical activity, sedentary behavior, body mass index (BMI), waist and hip circumferences, waist-to-hip ratio, and weight change and pre- and postmenopausal breast cancer risk were identified in PubMed up to 30 April 2017. Random-effects meta-analyses were conducted to summarize the relative risks across studies.

RESULTS

One hundred and twenty-six observational cohort studies comprising over 22,900 premenopausal and 103,000 postmenopausal breast cancer cases were meta-analyzed. Higher physical activity was inversely associated with both pre- and postmenopausal breast cancers, whereas increased sitting time was positively associated with postmenopausal breast cancer. Although higher early adult BMI (ages 18-30 years) was inversely associated with pre- and postmenopausal breast cancers, adult weight gain and greater body adiposity increased breast cancer risk in postmenopausal women, and the increased risk was evident for HR+ but not HR- breast cancers, and among never but not current users of postmenopausal hormones. The evidence was less consistent in premenopausal women. There were no associations with adult weight gain, inverse associations with adult BMI (study baseline) and hip circumference, and non-significant associations with waist circumference and waist-to-hip ratio that were reverted to positive associations on average in studies accounting for BMI. No significant associations were observed for HR-defined premenopausal breast cancers.

CONCLUSION

Better understanding on the impact of these factors on pre- and postmenopausal breast cancers and their subtypes along the life course is needed.

Targeting of PP2Cδ By a Small Molecule C23 Inhibits High Glucose-Induced Breast Cancer Progression In Vivo

Aims: Epidemiologic evidence indicates that diabetes may increase risk of breast cancer (BC) and mortality in patients with cancer. The pathophysiological relationships between diabetes and cancer are not fully understood, and personalized treatments for diabetes-associated BC are urgently needed. Results: We observed that high glucose (HG), via activation of nuclear phosphatase PP2Cδ, suppresses p53 function, and consequently promotes BC cell proliferation, migration, and invasion. PP2Cδ expression is higher in tumor tissues from BC patients with hyperglycemia than those with normoglycemia. The mechanisms underlying HG stimulation of PP2Cδ involve classical/novel protein kinase-C (PKC) activation and GSK3β phosphorylation. Reactive oxygen species (ROS)/NF-κB pathway also mediates HG induction of PP2Cδ. Furthermore, we identified a 1,5-diheteroarylpenta-1,4-dien-3-one (Compound 23, or C23) as a novel potent PP2Cδ inhibitor with a striking cytotoxicity on MCF-7 cells through cell-based screening assay for growth inhibition and activity of a group of curcumin mimics. Beside directly inhibiting PP2Cδ activity, C23 blocks HG induction of PP2Cδ expression via heat shock protein 27 (HSP27) induction and subsequent ablation of ROS/NF-κB activation. C23 can thus significantly block HG-triggered inhibition of p53 activity, leading to the inhibition of cancer cell proliferation, migration, and invasion. In addition, hyperglycemia promotes BC development in diabetic nude mice, and C23 inhibits the xenografted BC tumor growth. Conclusions and Innovation: Our findings elucidate mechanisms that may have contributed to diabetes-associated BC progression, and provide the first evidence to support the possible alternative therapeutic approach to BC patients with diabetes. Antioxid. Redox Signal. 30, 1983-1998.

Serum glucose and insulin and risk of cancers of the breast, endometrium, and ovary in postmenopausal women

Limited evidence suggests that hyperinsulinemia may contribute to the risk of breast, endometrial, and, possibly, ovarian cancer. The aim of this study was to assess the association of serum glucose and insulin with risk of these cancers in postmenopausal women, while taking into account potential confounding and modifying factors. We studied 21 103 women with fasting baseline insulin and glucose measurements in a subsample of the Women's Health Initiative. The subsample was composed of four studies within Women's Health Initiative with different selection and sampling strategies. Over a mean of 14.7 years of follow-up, 1185 breast cancer cases, 156 endometrial cancer cases, and 130 ovarian cancer cases were diagnosed. We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) by quartile of glucose or insulin. Serum insulin was positively associated with breast cancer risk (multivariable-adjusted HR for highest vs. lowest quartile 1.41, 95% CI: 1.16-1.72, Ptrend<0.0003), and glucose and insulin were associated with roughly a doubling of endometrial cancer risk (for glucose: HR: 2.00, 95% CI: 1.203.35, Ptrend=0.01; for insulin: HR: 2.39, 95% CI: 1.32-4.33, Ptrend=0.008). These associations remained unchanged or were slightly attenuated after mutual adjustment, adjustment for serum lipids, and assessment of possible reverse causation. Glucose and insulin showed no association with ovarian cancer. Our findings provide support for a role of insulin-related pathways in the etiology of cancers of the breast and endometrium. However, because of the unrepresentative nature of the sample, our results need confirmation in other populations.

Association of Dyslipidemia, Increased Insulin Resistance, and Serum CA 15-3 with Increased Risk of Breast Cancer in Urban Areas of North and Central India

Objective:

This study aims to determine the association of dyslipidemia and increased insulin resistance (IR) with increased breast cancer (BC) risk.

Materials and Methods:

The study group comprised 110 premenopausal and 143 postmenopausal, untreated female BC patients in the age range of 29–72 years. Control group consisted of 117 premenopausal and 141 postmenopausal healthy females in the age range of 23–75. Approximately 8-ml blood samples were drawn to measure various biochemical parameters. Serum glucose, total cholesterol, triglyceride (TG), and high-density lipoprotein-cholesterol were measured. Very low-density lipoprotein-cholesterol (VLDL-C) and LDL-C were calculated using Friedewald's formula. Serum insulin and serum CA 15-3 were estimated by immune enzymatic assay. IR was assessed using homeostasis model assessment IR index (HOMA-IR).

Results:

Clinical variables in the case and control groups were compared using the unpaired Student's t-test. The crude and adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by binary logistic regression analysis. Pearson's correlation analysis was used to determine the association between CA 15-3 and variables of interest. Total cholesterol, TG, LDL, VLDL, serum glucose, serum insulin, HOMA-IR, and serum CA 15-3 were significantly higher (P < 0.001) in BC patients compared to those in controls. Significant adjusted ORs with 95% CI were found to be fasting glucose, total cholesterol, and TGs. We also found a significant positive correlation between total cholesterol, TG, LDL, serum glucose, serum insulin, HOMA-IR, and serum CA 15-3.

Conclusion:

This study confirms the association between dyslipidemia, IR, and increased BC risk.

Body mass index had different effects on premenopausal and postmenopausal breast cancer risks: a dose-response meta-analysis with 3,318,796 subjects from 31 cohort studies

Background

There is sufficient evidence supporting a relationship between increased body mass index (BMI) and an increased risk for breast cancer among postmenopausal women. However, most studies have found a decreased risk for premenopausal breast cancer. This study was conducted to find out the different effects of BMI on the risk of breast cancer among premenopausal and postmenopausal women, and explore the potential factors that influence the associations.

Methods

A dose-response meta-analysis with 3,318,796 participants from 31 articles was conducted. Cohort studies that included BMI and corresponding breast cancer risk were selected through various databases including PubMed, Medline, Web of Science, the China National Knowledge Infrastructure (CNKI) and Chinese Scientific Journals (VIP). Random effects models were used for analyzing the data.

Results

The summary relative risks (RRs) were 1.33 (95%CI: 1.20–1.48) and 0.94(95%CI: 0.80–1.11) among postmenopausal and premenopausal women, respectively. The dose-response meta-analysis indicated a positive non-linear association between BMI and breast cancer risk among postmenopausal women, and compared to the mean level of the normal BMI category (21.5 kg/m²) the RR in total postmenopausal women were1.03 (95% CI: 1.02–1.05) per 1 kg/m² increment. However, no statistically significant association among total premenopausal women was detected. In subgroup analysis among European premenopausal women, the summary RR was 0.79(95%CI: 0.70–0.88). The non-linear relationship showed a negative non-linear association between BMI and breast cancer risk among European premenopausal women. When compared to the mean level of the normal BMI category, the RRs were 0.98 (95%CI: 0.96–1.00) per 1 kg/m² increment, respectively.

Conclusions

In line with previous studies BMI had different effects on pre-menopausal and postmenopausal breast cancer risk. However, contrary to previous studies, a high BMI was not associated with decreased risk in total pre-menopausal women. More research is needed to better understand these differences.

Electronic supplementary material

The online version of this article (10.1186/s12889-017-4953-9) contains supplementary material, which is available to authorized users.

Metabolic Syndrome and Breast Cancer Risk

Objective

The study was meant to estimate the prevalence of metabolic syndrome in patients with breast cancer and to establish its role as an independent risk factor on occurrence of breast cancer.

Materials and Methods

Fifty women aged between 40 and 80 years with breast cancer and fifty controls of similar age were assessed for metabolic syndrome prevalence and breast cancer risk factors, including age at menarche, reproductive status, live births, breastfeeding, and family history of breast cancer, age at diagnosis of breast cancer, body mass index, and metabolic syndrome parameters.

Results

Metabolic syndrome prevalence was found in 40.0% of breast cancer patients, and 18.0% of those in control group (P = 0.02). An independent and positive association was seen between metabolic syndrome and breast cancer risk (odds ratio = 3.037; 95% confidence interval 1.214-7.597).

Conclusions

Metabolic syndrome is more prevalent in breast cancer patients and is an independent risk factor for breast cancer.

Effects of Serum Triglycerides on Prostate Cancer and Breast Cancer Risk: A Meta-Analysis of Prospective Studies

Epidemiological studies show conflicting results regarding the link between serum triglyceride and the risk of prostate cancer and breast cancer. Therefore, we performed a meta-analysis of prospective studies to clarify this association. We searched PubMed, EMBASE, the Chinese Biomedical Database (CBM), and the China National Knowledge Infrastructure (CNKI) database to identify relevant prospective studies of the relationship between serum triglyceride and prostate cancer and breast cancer risk. Study-specific estimates adjusting for potential confounders were combined to evaluate a summary relative risks (RRs) and 95% confidence intervals (95% CIs) using a fixed- or random-effects model. A total of 11 prospective studies (619,410 subjects and 15,691 incident prostate cancer patients) and 8 prospective studies (590,878 subjects and 12,177 incident breast cancer patients) were respectively included in our meta-analysis to assess the associations of serum triglyceride with prostate cancer and breast cancer risk. The pooled adjusted RR estimates for prostate cancer and breast cancer for the highest versus the lowest exposure levels of serum triglycerides were 0.95 (95% CI: 0.87-1.04) and 0.94 (95% CI: 0.87-1.00), respectively. Additionally, a dose-response analysis revealed that serum levels of triglycerides were not associated with the risk of prostate cancer and breast cancer. We found that serum triglyceride was not related to the risk of prostate cancer and breast cancer.

Elevated fasting blood glucose is associated with increased risk of breast cancer: outcome of case-control study conducted in Karachi, Pakistan

BACKGROUND

There are several validated risk factors for breast cancer. However the legitimacy of elevated fasting blood glucose (FBG) is not well established. This study was designed to assess this parameter as a risk factor for breast cancer among pre- and post-menopausal women.

MATERIALS AND METHODS

This case-control study was conducted at Department of Biochemistry, University of Karachi from June 2010 to August 2014. Simple random sampling technique was used to collect data of study subjects comprising 175 diagnosed breast cancer patients with positive histopathology from Breast Clinic, surgical unit-1, Civil Hospital, Karachi and 175 healthy controls from various screening programs. Blood samples were analyzed for FBG and serum insulin.

RESULTS

FBG, HOMA-IR, systolic and diastolic blood pressure were significantly raised in breast cancer cases when compared to control subjects. Cases and controls were further categorized in to two groups using cutoff value of 110 mg/dl to distinguish subjects into normal fasting glucose (<110 mg/dl) and having impaired fasting glucose (≥110-≤125 mg/dl) or diabetes (≥126 mg/dl). Odds ratios were found to be 1.57, 2.15 and 1.17 in overall, pre-menopausal and post-menopausal groups, respectively. (all p<0.05).

CONCLUSIONS

A statistically significant risk of breast cancer exists in women having elevated fasting blood glucose levels, corresponding to prediabetes and diabetes, among pre and postmenopausal ages, with comparatively greater effects in the premenopausal group.

Serum Lipids and Breast Cancer Risk: A Meta-Analysis of Prospective Cohort Studies

Purpose

Epidemiologic studies exploring causal associations between serum lipids and breast cancer risk have reported contradictory results. We conducted a meta-analysis of prospective cohort studies to evaluate these associations.

Methods

Relevant studies were identified by searching PubMed and EMBASE through April 2015. We included prospective cohort studies that reported relative risk (RR) estimates with 95% confidence intervals (CIs) for the associations of specific lipid components (i.e., total cholesterol [TC], high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol [LDL-C], and triglycerides [TG]) with breast cancer risk. Either a fixed- or a random-effects model was used to calculate pooled RRs.

Results

Fifteen prospective cohort studies involving 1,189,635 participants and 23,369 breast cancer cases were included in the meta-analysis. The pooled RRs of breast cancer for the highest versus lowest categories were 0.96 (95% CI: 0.86–1.07) for TC, 0.92 (95% CI: 0.73–1.16) for HDL-C, 0.90 (95% CI: 0.77–1.06) for LDL-C, and 0.93 (95% CI: 0.86–1.00) for TG. Notably, for HDL-C, a significant reduction of breast cancer risk was observed among postmenopausal women (RR = 0.77, 95% CI: 0.64–0.93) but not among premenopausal women. Similar trends of the associations were observed in the dose-response analysis.

Conclusions

Our findings suggest that serum levels of TG but not TC and LDL-C may be inversely associated with breast cancer risk. Serum HDL-C may also protect against breast carcinogenesis among postmenopausal women.

Cholesterol and breast cancer risk: a systematic review and meta-analysis of prospective studies

The objective of the present study was to conduct the first systematic review and meta-analysis of prospective studies investigating the associations between total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C) levels and the risk of breast cancer. Relevant studies were identified in PubMed (up to January 2014). Inclusion criteria were original peer-reviewed publications with a prospective design. Random-effects models were used to estimate summary hazard ratios (HR) and 95% CI. Distinction was made between studies that did or did not exclude cancer cases diagnosed during the first years of follow-up, thereby eliminating potential preclinical bias. Overall, the summary HR for the association between TC and breast cancer risk was 0.97 (95% CI 0.94, 1.00; dose-response per 1 mmol/l increment, thirteen studies), and that between HDL-C and breast cancer risk was 0.86 (95% CI 0.69, 1.09; dose-response per 1 mmol/l increment, six studies), with high heterogeneity (I2= 67 and 47%, respectively). For studies that eliminated preclinical bias, an inverse association was observed between the risk of breast cancer and TC (dose-response HR 0.94 (95% CI 0.89, 0.99), seven studies, I2= 78%; highest v. lowest HR 0.82 (95% CI 0.66, 1.02), nine studies, I2= 81%) and HDL-C (dose-response HR 0.81 (95% CI 0.65, 1.02), five studies, I2= 30 %; highest v. lowest HR 0.82 (95% CI 0.69, 0.98), five studies, I2= 0%). There was no association observed between LDL-C and the risk of breast cancer (four studies). The present meta-analysis confirms the evidence of a modest but statistically significant inverse association between TC and more specifically HDL-C and the risk of breast cancer, supported by mechanistic plausibility from experimental studies. Further large prospective studies that adequately control for preclinical bias are needed to confirm the results on the role of cholesterol level and its fractions in the aetiology of breast cancer.

Hypertension and subsequent genitourinary and gynecologic cancers risk: a population-based cohort study

Although a relationship between hypertension and the development of renal cancer and other types of cancer have been proposed for decades, the results of epidemiologic studies remain inconclusive. This study was conducted to evaluate the association between hypertension and genitourinary and gynecologic cancers in Taiwan.In this study, we conducted a populated-based retrospective cohort study by using data from the Taiwanese National Health Insurance program. The study period was from 2000 to 2011, and the cohort comprised 111,704 insurants: 57,961 patients with hypertension and 53,743 patients without hypertension. A Cox proportional hazard regression analysis was performed to estimate the effects of hypertension on genitourinary and gynecologic cancers risk.Among the patients with hypertension, the risks of developing renal and uterine corpus cancers were significantly higher in the hypertension group than they were in the nonhypertension group. Further stratified analyses by sex, age, and hypertension duration revealed distinct cancer-specific patterns. Higher cancer risk appears to be more obvious among younger hypertensive patients with longer follow-up time.The results of this study indicate that Taiwanese patients with hypertension have higher risks for some types of cancer, and cancer-specific patterns vary by sex, age, and hypertension duration.

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.

Serum glucose and risk of cancer: a meta-analysis

BACKGROUND

Raised serum glucose has been linked to increased risk of many solid cancers. We performed a meta-analysis to quantify and summarise the evidence for this link.

METHODS

Pubmed and Embase were reviewed, using search terms representing serum glucose and cancer. Inclusion and exclusion criteria focused on epidemiological studies with clear definitions of serum glucose levels, cancer type, as well as well-described statistical methods with sufficient data available. We used 6.1 mmol/L as the cut-off for high glucose, consistent with the WHO definition of metabolic syndrome. Random effects analyses were performed to estimate the pooled relative risk (RR).

RESULTS

Nineteen studies were included in the primary analysis, which showed a pooled RR of 1.32 (95% CI: 1.20 - 1.45). Including only those individuals with fasting glucose measurements did not have a large effect on the pooled RR (1.32 (95% CI: 1.11-1.57). A stratified analysis showed a pooled RR of 1.34 (95% CI: 1.02-1.77) for hormonally driven cancer and 1.21 (95% CI: 1.09-1.36) for cancers thought to be driven by Insulin Growth Factor-1.

CONCLUSION

A positive association between serum glucose and risk of cancer was found. The underlying biological mechanisms remain to be elucidated but our subgroup analyses suggest that the insulin- IGF-1 axis does not fully explain the association. These findings are of public health importance as measures to reduce serum glucose via lifestyle and dietary changes could be implemented in the context of cancer mortality.

Body mass index and risk of breast cancer: a nonlinear dose-response meta-analysis of prospective studies

The role of Body Mass Index (BMI) for Breast Cancer (BC) remains to be great interest for a long time. However, the precise effect of nonlinear dose-response for BMI and BC risk is still unclear. We conducted a dose-response meta-analysis to quantitatively assess the effect of BMI on BC risk. Twelve prospective studies with 4,699 cases identified among 426,199 participants and 25 studies of 22,809 cases identified among 1,155,110 participants in premenopausal and postmenopausal groups, respectively, were included in this meta-analysis. Significant non-linear dose-response (P < 0.001) association was identified between BMI and BC risk in postmenopausal women. Individuals with BMI of 25, 30, and 35 kg/m² yielded relative risks (RRs) of 1.02 [95% confidence interval (CI): 0.98–1.06], 1.12 (95% CI: 1.01–1.24), and 1.26 (95% CI: 1.07–1.50), respectively, when compared to the mean level of the normal BMI range. However, inverse result though not significant was observed in premenopausal women. In conclusion, the results of this meta-analysis highlighted that obesity contributed to increased BC risk in a nonlinear dose-response manner in postmenopausal women, and it is important to realize that body weight control may be a crucial process to reduce BC susceptibility.

Metabolic syndrome and outcomes following early-stage breast cancer

The prevalence of risk factors contributing to metabolic syndrome (MetS) is increasing, and numerous components of MetS are associated with increased primary breast cancer (BC) risk. However, less is known about the relationship of MetS to BC outcomes. The aim of this study was to evaluate whether MetS, characterized by increased weight, hypertension, low HDL-cholesterol, high triglycerides, and diabetes or impaired glucose tolerance, is associated with risk of second breast cancer events (SBCE) and BC-specific mortality. Retrospective cohort study of women diagnosed with incident early-stage (I-II) BC between 1990 and 2008, enrolled in an integrated health plan. Outcomes of interest were SBCE, defined as recurrence or second primary BC, and BC-specific mortality. We used multivariable Cox proportional hazards models to estimate adjusted hazard ratios (HR) and 95% confidence intervals (CI) for time-varying exposure to MetS components while accounting for potential confounders and competing risks. Among 4,216 women in the cohort, 26% had ≥3 MetS components and 13% developed SBCE during median follow-up of 6.3 years. Compared to women with no MetS components, presence of MetS (≥3 components) was associated with increased risk of SBCE (HR = 1.50, 95% CI 1.08-2.07) and BC-specific mortality (HR = 1.65, 95% CI 1.02-2.69). Of the individual components, only increased weight was associated with increased risk of SBCE (HR = 1.26, 95% CI 1.06-1.49). MetS is associated with modestly increased risk of SBCE and BC-specific mortality. Given the growing population of BC survivors, further research in larger and more diverse populations is warranted.

Metabolic syndrome and breast cancer prognosis

Metabolic syndrome (MS), conventionally defined by the presence of at least three out of five dysmetabolic traits (abdominal obesity, hypertension, low plasma HDL-cholesterol, high plasma glucose and high triglycerides), has been associated with an increased risk of several age-related chronic diseases, including breast cancer (BC). This may have prognostic implications for BC survivors. 2,092 early stage BC survivors aged 35-70, recruited in eleven Italian centres 0-5 years after surgical treatment (1.74 years on average), were followed-up over 2.8 years on average for additional BC-related events, including BC-specific mortality, distant metastasis, local recurrences and contralateral BC. At recruitment, 20 % of the patients had MS. Logistic regression models were carried out to generate OR and 95 % confidence intervals (CI) for new BC events associated with MS, adjusting for baseline pathological prognostic factors. New BC events occurred in 164 patients, including 89 distant metastases. The adjusted ORs for women with MS versus women without any MS traits were 2.17 (CI 1.31-3.60) overall, and 2.45 (CI 1.24-4.82) for distant metastasis. The OR of new BC events for women with only one or two MS traits was 1.40 (CI 0.91-2.16). All MS traits were positively associated with new BC events, and significantly so for low HDL and high triglycerides. MS is an important prognostic factor in BC. As MS is reversible through lifestyle changes, interventions to decrease MS traits in BC patients should be implemented in BC clinics.

Metabolic syndrome and postmenopausal breast cancer: systematic review and meta-analysis

OBJECTIVE

The role of metabolic syndrome (MS) and its individual components in postmenopausal breast cancer (PBC) risk is still unclear. We reviewed and summarized epidemiological studies assessing the association of MS with the risk of PBC.

METHODS

We conducted an electronic search, without restrictions, for articles published before October 31, 2012. Every included study was to report risk estimates with 95% CIs for the association between MS and PBC. Study-specific estimates were pooled using random-effects models.

RESULTS

Nine articles (with 6,417 cancer cases), all published in English, were included in the meta-analysis. MS was associated with a 52% increase in cancer risk (P < 0.001)-for the most part confined to noncohort studies (109% increased risk); the risk estimates changed little, depending on populations (United States and Europe) and definition of the syndrome (traditional vs nontraditional). The risk estimates for PBC were 1.12 (P = 0.068) for higher values of body mass index/waist circumference, 1.19 (P = 0.005) for hyperglycemia (higher fasting glucose or diabetes), 1.13 (P = 0.027) for higher blood pressure, 1.08 (P = 0.248) for higher triglycerides, and 1.39 (P = 0.008) for lower high-density lipoprotein cholesterol. All these estimates were lower than those associated with MS in the same studies.

CONCLUSIONS

MS is associated with a moderately increased risk of PBC. No single component explains the risk conveyed by the full syndrome.

Insulin and IGFs in obesity-related breast cancer

Obesity and the Metabolic Syndrome are associated with multiple factors that may cause an increased risk for cancer and cancer-related mortality. Factors involved include hyperinsulinemia, hyperglycemia, hyperlipidemia and IGFs. Insulin resistance is also associated with alterations in the levels of proinflammatory cytokines, chemokines, adipokines (leptin, adiponectin) that may also be contributing factors. The insulin family of proteins is ubiquitously expressed and has pleiotropic effects on metabolism and growth. However insulin, IGF-1 and particularly IGF-2 have been identified as tumor promoters in multiple studies. Mouse models have focused on insulin and IGF-1 and their receptors as being involved in tumor progression and metastases. The role of the insulin receptor as either mediating the effects on tumors or as compensating for the insulin-like growth factor receptor has arisen. Its role has been supported by preclinical studies and the importance of insulin resistance and hyperinsulinemia in obesity and early diabetes. Since the focus of this review is the insulin-family we will focus on insulin, IGF-1 and IGF-2.

Association of cancer with moderately impaired renal function at baseline in a large, representative, population-based cohort followed for up to 30 years

Patients with chronic renal failure show a greater incidence of malignancies. We evaluated whether moderately impaired renal function at baseline influenced risk of all cancers during long-term follow in young persons. Our cohort included 33,346 subjects, aged 26-61 years at baseline, in a representative, population-based study enrolling subjects from 1974 to 1992. Median follow-up time was 28 years. Plasma creatinine was analyzed as a single measure at baseline. Incident cases of cancer were identified from the Swedish Cancer Registry. We studied 24,552 subjects from the cohort. To account for the unique sampling design, participants were divided by sex and age at baseline into 1,132 older men (age 60), 14,254 younger men (age 40-52), 7,498 older women (age 47-57) and 1,688 younger women (age 35-43). Glomerular filtration rate (GFR) was estimated using the CKD-EPI formula. Patients were classified as having either normal to mildly impaired kidney function (eGFR ≥ 60 mL/min/1.73 m(2) ), or moderate kidney dysfunction (eGFR<60 mL/min/1.73 m(2) ). We calculated the risk of all cancers using competing risks regression. Overall, 6,595 participants were diagnosed with cancer, and 854 subjects (3.5%) had moderately impaired renal dysfunction at baseline. There was a significant association between moderately decreased GFR and subsequent risk of kidney cancer in younger men (hazard ratio, 3.38; 95% CI, 1.48 to 7.71; p = 0.004). However, we found no association with overall long-term cancer risk. Our confirmation of an association between moderately impaired renal function and risk of kidney cancer in younger men requires further exploration of high-risk groups and biological mechanisms.

Blood glucose concentrations and breast cancer risk in women without diabetes: a meta-analysis

PURPOSE

Some studies have suggested an increased risk of breast cancer associated with elevated fasting serum glucose in nondiabetic subjects. Given how common both breast cancer and impaired glucose tolerance are in our aging societies, this is an important issue for public health.

METHODS

We performed a systematic review of prospective cohort studies that examined the association between elevated serum glucose levels in nondiabetic subjects (levels below 7.0 mml/L) and the subsequent risk of breast cancer. We performed a systematic literature search and extracted relevant data in a standard way. We then computed summary relative risks (SRR) and 95 % confidence intervals using a random effects model applied on the risk of highest versus lowest quantile of serum glucose concentrations.

RESULTS

Ten cohort studies were retrieved. The SRR for all studies was 1.11 (1.00-1.23), with no evidence of heterogeneity or publication bias. The SRR was not affected when the analysis was restricted to the 8 studies that reported results for fasting subjects (SRR = 1.11; 95 % CI 0.98-1.25). Three studies provided BMI-unadjusted and BMI-adjusted SRRs of 1.24 (95 % CI 0.60-2.56) and 1.20 (95 % CI 0.63-2.27), respectively. Similar magnitudes of associations were observed in sensitivity analyses, but statistical significance was lost.

CONCLUSION

In nondiabetic subjects, the risk of breast cancer associated with fasting serum glucose levels seems to be small. Potential limitations to this meta-analysis include the fact that not all studies reported risks adjusted for adiposity and that serum glucose levels of comparison groups were variable across studies.

Impact of overweight and obesity on postmenopausal breast cancer: analysis of 20-year data from Switzerland

PURPOSE

Greater body fatness has been identified as a risk factor for postmenopausal breast cancer. For countries with low overweight/obesity rates, data on prevalence and time course of overweight/obesity in women with breast cancer in comparison to women in the general population is limited. The Swiss female population is distinctive for two reasons: (a) low rates of overweight/obesity compared with other western countries, and (b) no obesity epidemic, i.e. stable rates of overweight/obesity for more than 10 years.

METHODS

Overweight and obesity were analyzed in 51 to 80-year-old breast cancer patients initially diagnosed between 1990 and 2009. Patient data was derived from the Basel Breast Cancer Database (BBCD). This data was compared with the data of women of the same age from the four Swiss Health Surveys (SHS) conducted between 1992 and 2007. Differences between measured (BBCD) and self-reported (SHS) data were corrected using equations approved for the Swiss population.

RESULTS

Of 958 postmenopausal BBCD patients, 32% were overweight and 20% were obese. Of the 14,476 women of the SHS, 38% were overweight and 17% were obese. In the BBCD, there was no change in the prevalence of overweight/obesity over the last 20 years. The four SHS show a convex curvature for obesity, i.e. a transient increase. No significant differences were observed between BBCD and corrected SHS data for overweight and obesity during this period.

CONCLUSIONS

In this Swiss study group with a comparably low prevalence of overweight and obesity, no association between body fatness and postmenopausal breast cancer was observed.

Impaired glucose metabolism and diabetes and the risk of breast, endometrial, and ovarian cancer

BACKGROUND

Epidemiological evidence indicates that individuals with type 2 diabetes are at an increased risk of cancer. Elevated glucose levels, below the diagnostic threshold for diabetes, have also been suggested to be associated with increased cancer risks.

METHODS

We investigated possible associations between glucose levels and the risk of breast, endometrial, and ovarian cancer in a cohort of more than 230,000 women, for which information on outcome and potential confounders was obtained by record linkage to population-based registers.

RESULTS

Diabetes was associated with an increased risk of postmenopausal breast cancer (HR = 1.22, 95% CI 1.04-1.43). An indication of a slightly elevated breast cancer risk was also found in postmenopausal women with impaired glucose metabolism (HR = 1.11, 95% CI 0.96-1.28). Diabetes (HR = 1.46, 95% CI 1.09-1.96) and impaired glucose metabolism (HR = 1.41, 95% CI 1.08-1.85) were associated with an increased risk of endometrial cancer. No associations were found between glucose levels and ovarian cancer risk. Following adjustment for BMI, estimates were attenuated for endometrial cancer, while point estimates for breast and ovarian cancer remained essentially unchanged.

CONCLUSIONS

Our results indicate that glucose levels below the diagnostic threshold for diabetes modify the risk not only of endometrial cancer but possibly also of postmenopausal breast cancer.

Associations between mammographic density and serum and dietary cholesterol

Although high mammographic density is a risk factor for postmenopausal breast cancer, its etiology remains unclear. We examined whether serum and dietary cholesterol, which increase breast cancer risk and are involved in endogenous estrogen formation, were associated with increased mammographic density. We conducted a cross-sectional analysis of 302 healthy, sedentary postmenopausal women, aged 50-74 years, enrolled in the Alberta Physical Activity and Breast Cancer Prevention Trial between 2003 and 2006. In multiple linear regression models, no significant associations were observed between serum lipids and percent density or dense tissue area (Percent density: b (change in square root percent density per unit change in cholesterol level) = -0.06 (95%CI = -0.26 to 0.13); b = 0.06 (95%CI = -0.48 to 0.61); and b = -0.11 (95%CI = -0.33 to 0.10) for total cholesterol, high-, and low-density lipoprotein, respectively; similar results found for dense area). Alcohol consumption modified the association between triglycerides and percent density (>1 drink/day: b = -0.94 (95%CI = -1.79 to -0.10); ≤ 1 drink/day: b = 0.19 (95%CI = -0.12 to 0.50); and no alcohol consumption: b = 0.15 (95%CI = -0.44 to 0.73). We found no evidence indicating any association between dietary and serum cholesterol levels and mammographic density.

Biomarkers of the metabolic syndrome and breast cancer prognosis

In spite of its public health importance, our understanding of the mechanisms of breast carcinogenesis and progress is still evolving. The metabolic syndrome (MS) is a constellation of biochemical abnormalities including visceral adiposity, hyperglycemia, hyperinsulinemia, dyslipidemia and high blood pressure. The components of the MS have all been related to late-stage disease and even to a poor prognosis of breast cancer through multiple interacting mechanisms. In this review, we aim to present a summary of recent advances in the understanding of the contribution of the MS to breast cancer with the emphasis on the role of biomarkers of the MS in the prognosis of breast cancer.

Repeated measures of serum glucose and insulin in relation to postmenopausal breast cancer

Experimental and epidemiological evidence suggests that circulating glucose and insulin may play a role in breast carcinogenesis. However, few cohort studies have examined breast cancer risk in association with glucose and insulin levels, and studies to date have had only baseline measurements of exposure. We conducted a longitudinal study of postmenopausal breast cancer risk using the 6% random sample of women in the Women's Health Initiative clinical trials whose fasting blood samples, provided at baseline and at years 1, 3 and 6, were analyzed for glucose and insulin. In addition, a 1% sample of women in the observational study, who had glucose and insulin measured in fasting blood samples drawn at baseline and in year 3, were included in the analysis. We used Cox proportional hazards models to estimate hazard ratios and 95% confidence intervals for the association of baseline and follow-up measurements of serum glucose and insulin with breast cancer risk. All statistical tests were 2-sided. Among 5,450 women with baseline serum glucose and insulin values, 190 incident cases of breast cancer were ascertained over a median of 8.0 years of follow-up. The highest tertile of baseline insulin, relative to the lowest, was associated with a 2-fold increase in risk in the total population (multivariable hazard ratio 2.22, 95% confidence interval 1.39-3.53) and with a 3-fold increase in risk in women who were not enrolled in the intervention arm of any clinical trial (multivariable hazard ratio 3.15, 95% confidence interval 1.61-6.17). Glucose levels showed no association with risk. Analysis of the repeated measurements supported the results of the baseline analysis. These data suggest that elevated serum insulin levels may be a risk factor for postmenopausal breast cancer.

A longitudinal study of the metabolic syndrome and risk of postmenopausal breast cancer

The metabolic syndrome, characterized by abdominal obesity, high blood glucose levels, impaired glucose tolerance, dyslipidemia, and hypertension, is associated with increased risk of type 2 diabetes and coronary heart disease. Several studies have examined the association of the individual components of the metabolic syndrome with breast cancer; to date, however, no study has assessed the metabolic syndrome per se in relation to breast cancer risk. Furthermore, previous studies have relied only on baseline assessment of components of the syndrome. Therefore, we assessed the association of the metabolic syndrome with the risk of postmenopausal breast cancer among women in the 6% sample of subjects in the Women's Health Initiative clinical trial and the 1% sample of women in the observational study who had repeated measurements of the components of the syndrome during follow-up. We used Cox proportional hazards models to estimate hazard ratios and 95% confidence intervals for the association of breast cancer risk with the presence of the metabolic syndrome, as well as its components, at baseline and in time-dependent analyses. After exclusion of women with diabetes, among 4,888 women with baseline measurements, 165 incident cases of breast cancer were ascertained over a median of 8 years of follow-up. The presence of the metabolic syndrome at baseline was not associated with altered risk. Of the individual components measured at baseline, diastolic blood pressure showed a borderline positive association with breast cancer. In time-dependent covariate analyses, however, certain scenarios indicated a positive association between the metabolic syndrome and breast cancer, due primarily to positive associations with serum glucose, serum triglycerides, and diastolic blood pressure.

Physical activity and postmenopausal breast cancer: proposed biologic mechanisms and areas for future research

Convincing evidence now supports a probable preventive role for physical activity in postmenopausal breast cancer. The mechanisms by which long-term physical activity affect risk, however, remain unclear. The aims of this review were to propose a biological model whereby long-term physical activity lowers postmenopausal breast cancer risk and to highlight gaps in the epidemiologic literature. To address the second aim, we summarized epidemiologic literature on 10 proposed biomarkers, namely, body mass index (BMI), estrogens, androgens, sex hormone binding globulin, leptin, adiponectin, markers of insulin resistance, tumor necrosis factor-alpha, interleukin-6, and C-reactive protein, in relation to postmenopausal breast cancer risk and physical activity, respectively. Associations were deemed "convincing," "probable," "possible," or "hypothesized" using set criteria. Our proposed biological model illustrated the co-occurrence of overweight/obesity, insulin resistance, and chronic inflammation influencing cancer risk through interrelated mechanisms. The most convincing epidemiologic evidence supported associations between postmenopausal breast cancer risk and BMI, estrogens, and androgens, respectively. In relation to physical activity, associations were most convincing for BMI, estrone, insulin resistance, and C-reactive protein. Only BMI and estrone were convincingly (or probably) associated with both postmenopausal breast cancer risk and physical activity. There is a need for prospective cohort studies relating the proposed biomarkers to cancer risk and for long-term exercise randomized controlled trials comparing biomarker changes over time, specifically in postmenopausal women. Future etiologic studies should consider interactions among biomarkers, whereas exercise trials should explore exercise effects independently of weight loss, different exercise prescriptions, and effects on central adiposity.

Diabetes, metabolic syndrome, and breast cancer: a review of the current evidence

Incidences of breast cancer, type 2 diabetes, and metabolic syndrome have increased over the past decades with the obesity epidemic, especially in industrialized countries. Insulin resistance, hyperinsulinemia, and changes in the signaling of growth hormones and steroid hormones associated with diabetes may affect the risk of breast cancer. We reviewed epidemiologic studies of the association between type 2 diabetes and risk of breast cancer and the available evidence on the role of hormonal mediators of an association between diabetes and breast cancer. The combined evidence supports a modest association between type 2 diabetes and the risk of breast cancer, which appears to be more consistent among postmenopausal than among premenopausal women. Despite many proposed potential pathways, the mechanisms underlying an association between diabetes and breast cancer risk remain unclear, particularly because the 2 diseases share several risk factors, including obesity, a sedentary lifestyle, and possibly intake of saturated fat and refined carbohydrates, that may confound this association. Although the metabolic syndrome is closely related to diabetes and embraces additional components that might influence breast cancer risk, the role of the metabolic syndrome in breast carcinogenesis has not been studied and thus remains unknown.

Risk factors for breast cancer in Turkish women: a hospital-based case-control study

The aim of this study was to investigate the association between risk factors and breast cancer in Turkish women. In a hospital-based case-control study in Istanbul, 405 patients with histologically confirmed breast cancer were compared with 1050 controls, who were admitted to different departments of the same hospital. Unadjusted odds ratios (ORs) and 95% confidence intervals (CIs) for each risk factor were obtained from logistic regression analyses. Risk factors for breast cancer were found to be early menarche age (OR 3.87, 95% CI 2.46-6.08), use of alcohol (OR 3.87, 95% CI 1.79-8.37), history of diabetes (OR 3.31, 95% CI 2.36-4.64) or hypertension (OR 3.44, 95% CI 2.07-5.71), oral contraceptive use (OR 1.98, 95% CI 1.38-2.85) and hormone replacement therapy (HRT) use (OR 1.94, 95% CI 1.15-3.29). The findings of the present study indicated that history of diabetes or hypertension, use of alcohol, oral contraceptive and HRT, never having breastfed and delayed age at first birth associated with changing of lifestyle led to an increased risk of breast cancer in Turkish women.

Incidence of breast cancer among postmenopausal, hypertensive women

Elevated blood pressure has been proposed to be a risk factor for breast cancer but the results remain controversial. In this study, the incidence of breast cancer among 9,112 postmenopausal, hypertensive women included in the community-based hypertension register of the North Karelia project was assessed through the Finnish Cancer Registry. The mean follow-up time was 27 years. The incidence of breast cancer in hypertensive women in our cohort was similar to the age and period specific population-based rates for Eastern Finland [the standardised incidence ratio 0.96 (95% confidence interval 0.86-1.05)]. In the Cox regression analysis, there was no association between blood pressure levels, or use of antihypertensive (AH) drugs, and breast cancer incidence, when all women were considered. There was a statistically significant interaction of the use of AH drugs at baseline and the diastolic blood pressure (DBP). Among women who were not using AH drugs at baseline, the DBP level was positively associated with the subsequent risk of breast cancer (hazard ratio 1.26/10 mm Hg, 95% confidence interval 1.06-1.46). In women with AH drugs at baseline, the DBP had an opposite effect of borderline significance (hazard ratio 0.90/10 mm Hg, 95% confidence interval 0.78-1.01). In conclusion, breast cancer incidence among postmenopausal hypertensive patients in general does not differ from that of general population. Elevated DBP levels may be associated with an increased breast cancer risk among nonpharmacologically treated women.

Metabolic syndrome predicts prostate cancer in a cohort of middle-aged Norwegian men followed for 27 years

The aim of the study was to establish whether metabolic syndrome predicts the incidence of prostate cancer. The hypothesis was tested using the 27-year follow-up of the prospective cohort of 16,209 men aged 40-49 years who participated in the Oslo Study in 1972-1973. Men with established diabetes and men with cancer diagnosed before screening were excluded, leaving 15,933 for analyses. Metabolic syndrome is here composed of body mass index, nonfasting glucose, triglycerides, and blood pressure or drug-treated hypertension. Two analytical approaches were compared, namely, predefined (adjusted from National Cholesterol Education Program) and quartile values of risk factors. Age, body mass index, and sedentary versus intermediate physical activity at work were significant predictors in univariate proportional hazards regression analyses. Combinations of any two (relative risk = 1.23; p = 0.04) or any three (relative risk = 1.56; p = 0.00) factors of the metabolic syndrome using quartile values of risk factors were predictive of prostate cancer. The number of cases for four factors was too small for analyses. Predefined values of the risk factors were not found to be predictive. In conclusion, metabolic syndrome was found to predict prostate cancer during 27 years of follow-up, indicating an association between insulin resistance and the incidence of prostate cancer.

Hypertension, diuretics and breast cancer risk

It is unclear whether hypertension and antihypertensive medication use are associated with breast cancer. In order to examine these associations, we conducted a case-control study among women aged 50-75 years. Breast cancer cases were ascertained via a population-based cancer registry (n=523) and controls were ascertained via random-digit-dialing (n=131). Participants completed a self-administered questionnaire which queried history of hypertension, antihypertensive medication use and risk factors. Unconditional logistic regression was used to estimate the odds ratio (OR) and 95% confidence intervals (CI), adjusted for age, body mass index (BMI), diabetes, smoking, alcohol use, menopausal status, family history of breast or ovarian cancer, age at first full-term pregnancy and education. History of treated hypertension was associated with significant increased risk of breast cancer (OR, 1.77; 95% CI, 1.04-3.03) and this association appeared only in women with BMI > or =25 kg/m(2) (OR, 2.30; 95% CI, 1.12-4.71). Diuretic use was also associated with elevated breast cancer risk (OR, 1.79; 95% CI, 1.07-3.01). The risk associated with diuretic use increased with duration of use (P for trend, <0.01). Use of other blood pressure medications was not found to be associated with breast cancer risk. These results support a positive association between treated hypertension, diuretic use and breast cancer risk among women aged 50-75 years.

Fasting blood glucose and cancer risk in a cohort of more than 140,000 adults in Austria

AIMS/HYPOTHESIS

We investigated relations between fasting blood glucose and the incidence of cancer.

METHODS

A population-based cohort of more than 140,000 Austrian adults (63,585 men, 77,228 women) was followed over an average of 8.4 years. Incident cancer (other than non-melanoma skin cancers) was ascertained by a population-based cancer registry (n=5,212). Cox proportional-hazards models were used to estimate hazard rate ratios (HR) stratified for age and adjusted for smoking, occupational group and body mass index.

RESULTS

The highest fasting blood glucose category (> or =7.0 mmol/l) was weakly associated with all cancers combined (HR 1.20; 95% CI, 1.03-1.39 in men and 1.28; 95% CI, 1.08-1.53 in women) relative to the reference level (4.2-5.2 mmol/l). The strongest association was found for liver cancer in men (HR 4.58; 95% CI, 1.81-11.62). Positive associations between fasting hyperglycaemia (6.1-6.9 or > or =7.0 mmol/l) and cancer incidence were also observed for non-Hodgkin's lymphoma in men, and for colorectal and bladder cancer in women. Breast cancer in women diagnosed at or after age 65 was also associated with fasting blood glucose > or =7.0 mmol/l. Positive associations with glucose values >5.3 mmol/l were noted for thyroid cancer, gallbladder/bile duct cancer and multiple myeloma in men and women combined.

CONCLUSIONS/INTERPRETATION

These findings provide further evidence that elevated blood glucose is associated with the incidence of several types of cancer in men and women.

A Prospective Study of Hemoglobin A1c Concentrations and Risk of Breast Cancer in Women

Impaired glucose metabolism and hyperinsulinemia have been hypothesized to increase breast cancer risk. However, findings from observational studies relating blood concentrations of hyperinsulinemia markers to breast cancer risk have been inconsistent. We prospectively evaluated whether hemoglobin A1c (HbA1c) concentrations predict breast cancer risk in a large female cohort. We included 27,110 female participants of the Women's Health Study who were, at baseline, free of cancer and had usable blood specimens as well as sufficient information on potential risk factors for breast cancer. Relative risks (RR) and 95% confidence intervals (95% CI) were estimated from Cox proportional hazards regression models. All Ps were two sided. During an average of 10 years of follow-up, 790 incident cases of invasive breast cancer were confirmed. Higher baseline HbA1c levels were not associated with an increased risk of breast cancer. The multivariate RR for the highest relative to the lowest quintile of HbA1c levels was 0.87 (95% CI, 0.69-1.10; Ptrend = 0.22). Higher HbA1c levels were also not associated with an increased risk of breast cancer according to alternative clinical cutoff points for HbA1c or in the analyses stratified by body mass index or according to certain tumor characteristics. However, a weakly inverse association was noted among postmenopausal women, especially among those who had never used hormone therapy. There was also a weakly inverse association between HbA1c levels and estrogen receptor–negative breast tumors. These data suggest that higher HbA1c concentrations do not seem to increase risk of breast cancer among apparently healthy women. (Cancer Res 2006; 66(5): 2869-75)

Associations among circulating sex hormones, insulin-like growth factor, lipids, and mammographic density in postmenopausal women

OBJECTIVE

Hormone therapy use has been positively associated with mammographic density in several studies. However, few studies have examined the association between endogenous hormone levels and mammographic density. Therefore, we evaluated the relationship of endogenous sex hormones, insulin-like growth factor (IGF), and lipids with mammographic density in 88 overweight, postmenopausal women not taking hormone therapy.

METHODS

Percent density and dense area were evaluated as continuous measures using a computer-assisted program. We used multiple linear regression to evaluate the associations of sex hormones, IGF, and cholesterol with mammographic density, adjusting for confounders, including adiposity. We evaluated stratification by history of hormone therapy use (former versus never) and hormone therapy latency (<5 versus > or = 5 years).

RESULTS

Among former hormone therapy users, mammographic density was inversely associated with circulating levels of estrone (P = 0.01), estradiol (P = 0.003), free estradiol (P = 0.004), testosterone (P = 0.04), free testosterone (P = 0.02), androstenedione (P < 0.001), dehydroepiandrosterone (P = 0.01), and the ratio of IGF-I to its binding protein (IGF-I/IGFBP-3; P = 0.04). We found similar associations when we limited the analyses to women who had used hormone therapy within the past 5 years. We also noted positive associations of mammographic density with total cholesterol (P = 0.03) and low-density lipoprotein (P = 0.03) among former hormone therapy users. No associations were noted among women who had never used hormone therapy.

CONCLUSIONS

These results suggest that there is an inverse relationship between endogenous sex hormones and mammographic density in postmenopausal women among former users of hormone therapy. This is not consistent with the hormone therapy literature and should be confirmed in larger studies.