Relation between insulin resistance and breast cancer among Chilean women

Association between prediabetes and breast cancer: a comprehensive meta-analysis

BACKGROUND

Breast cancer accounts for up to 30% of cancer cases in women in the US. Diabetes mellitus has been recognized as a risk factor for breast cancer. Some studies have suggested that prediabetes may also be associated with breast cancer whereas other studies have shown no or an inverse association; thus, we conducted a meta-analysis to assess the risk of breast cancer in prediabetes.

METHODS

We searched PubMed/Medline, EMBASE, Google Scholar, and Scopus to identify studies that reported breast cancer risks in patients having prediabetes compared to normoglycemic patients. Binary random-effects model was used to calculate a pooled odds ratio (OR) with 95% confidence intervals. I2 statistics were used to assess heterogeneity. Leave-one-out sensitivity analysis and subgroup analyses were performed.

RESULTS

We analyzed 7 studies with 24,586 prediabetic and 224,314 normoglycemic individuals (783 and 5739 breast cancer cases, respectively). Unadjusted odds ratio (OR) for breast cancer was 1.45 (95% CI = 1.14, 1.83); adjusted OR was 1.19 (95% CI = 1.07, 1.34) in prediabetes. Subgroup analysis revealed a higher breast cancer risk in individuals aged less than 60 years (OR = 1.86, 95% CI = 1.39, 2.49) than in those aged 60 years or more (OR = 1.07, 95% CI = 0.97, 1.18). Subgroup analysis by median follow-up length indicated a higher risk of breast cancer for follow-ups of less than or equal to 2 years (OR = 2.34, 95% CI = 1.85, 2.95) than in those of over 10 years (OR = 1.1, 95% CI = 0.99, 1.23) and 6 to 10 years (OR = 1.03, 95% CI = 0.88, 1.21).

CONCLUSIONS

In conclusion, individuals with prediabetes have higher risk of developing breast cancer than those with normoglycemia, especially younger prediabetes patients. These individuals may benefit from early identification, monitoring, and interventions to reverse prediabetes.

Association Between Serum Insulin and C-Peptide Levels and Breast Cancer: An Updated Systematic Review and Meta-Analysis

Background

Several studies have reported that hyperinsulinemia plays a part in the etiology of breast cancer. However, no consensus has been reached. Therefore, we conducted a meta-analysis to explore the role of insulin and C-peptide in breast cancer.

Methods

A systematic search in PubMed, Embase, and The Cochrane Library was conducted up to September, 2020. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were used to measure effect sizes. Publication bias was assessed using the Egger test. Stability of these results was evaluated using sensitivity analyses.

Results

Fourteen articles including 27,084 cases and five articles including 2,513 cases were extracted for serum insulin levels and C-peptide levels. We found that C-peptide levels were positively associated with breast cancer with overall SMD = 0.37 (95% CI = 0.09–0.65, I² = 89.1%). Subgroup analysis by control source illustrated a positive relationship between breast cancer and C-peptide levels in population-based control. Subgroup analysis by C-peptide level indicated a positive correlation between breast cancer and C-peptide levels no matter C-peptide levels in case group is ≤3 ng/ml or >3 ng/ml. Subgroup analysis by age showed that C-peptide level positively correlated to breast cancer in women between the ages of 50 and 60. However, we did not identify any relationship between breast cancer and insulin levels (SMD = 0.22, 95% CI = −0.06–0.50, I² = 97.3%).

Conclusion

This meta-analysis demonstrated that C-peptide levels were positively related to breast cancer in women, and no relationship between insulin levels and breast cancer was found.

Hepatic lipids promote liver metastasis

Obesity predisposes to cancer and a virtual universality of nonalcoholic fatty liver disease (NAFLD). However, the impact of hepatic steatosis on liver metastasis is enigmatic. We find that while control mice were relatively resistant to hepatic metastasis, those which were lipodystrophic or obese, with NAFLD, had a dramatic increase in breast cancer and melanoma liver metastases. NAFLD promotes liver metastasis by reciprocal activation initiated by tumor-induced triglyceride lipolysis in juxtaposed hepatocytes. The lipolytic products are transferred to cancer cells via fatty acid transporter protein 1, where they are metabolized by mitochondrial oxidation to promote tumor growth. The histology of human liver metastasis indicated the same occurs in humans. Furthermore, comparison of isolates of normal and fatty liver established that steatotic lipids had enhanced tumor-stimulating capacity. Normalization of glucose metabolism by metformin did not reduce steatosis-induced metastasis, establishing the process is not mediated by the metabolic syndrome. Alternatively, eradication of NAFLD in lipodystrophic mice by adipose tissue transplantation reduced breast cancer metastasis to that of control mice, indicating the steatosis-induced predisposition is reversible.

Nonalcoholic fatty liver disease promotes liver metastasis in mice, likely due to lipid transfer to tumor cells.

Diabetes as a Risk Factor for Breast Cancer

Diabetes is one of the most important chronic conditions worldwide, and breast cancer is the most prevalent cancer in women worldwide. Several types of research have been conducted to ascertain the link between diabetes and its potential for increasing the risk of breast cancer. This research aims to determine the relationship between diabetes and breast cancer; patients with diabetes have a higher risk than the general population of developing cancer, and diabetes patients have a higher incidence and mortality of breast cancer. This research also reviewed the relationship between cytokines, the mitogenic effect of insulin-like growth factors, and breast cells. The review includes searching the PubMed database using the keywords "diabetes," "breast cancer," "risk factor," and "premenopausal." The search returned 53 articles used for review of this article.

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.

Breast cancer is associated to impaired glucose/insulin homeostasis in premenopausal obese/overweight patients

The association between breast cancer (BCa) presence and altered glucose/insulin metabolism is controversial likely due to an inaccurate insulin resistance (IR) assessment and inappropriate stratification of patients by body-mass index (BMI) and menopausal state. 148 women with suspect of sporadic BCa were stratified by BMI and menopause. Fasting levels of glucose, insulin, glycohemoglobin and selected IR-related and tumor-derived markers were measured. Glucose/insulin levels during OGTT were used to calculate insulin resistance/sensitivity indexes. Analysis of 77 BCa-bearing patients and 71 controls showed an association between BCa and IR as demonstrated by impaired glucose/insulin homeostasis (increased fasting- and OGTT-induced glucose levels) and deteriorated IR indexes, which was especially patent in premenopausal women. The association between BCa presence and IR was markedly influenced by BMI, being obese BCa patients significantly more insulin resistant than controls. BCa presence was associated to elevated levels of IR (glucose, triglycerides) and tumor-derived (VEGF) markers, especially in overweight/obese patients. BCa presence is associated to IR in overweight/obese premenopausal but not in premenopausal normal weight or postmenopausal women. Our data support a bidirectional relationship between dysregulated/imbalanced glucose/insulin metabolism and BCa, as tumor- and IR-markers are correlated with the impairment of glucose/insulin metabolism in overweight/obese premenopausal BCa patients.

Anthropometric, metabolic and molecular determinants of human epidermal growth factor receptor 2 expression in luminal B breast cancer

Genomic and trascriptomic profiling has recently contributed details to the characterization of luminal B breast cancer. We explored the contribution of anthropometric, metabolic, and molecular determinants to the multifaceted heterogeneity of this breast cancer subtype, with a specific focus on the association between body mass index (BMI), pre-treatment fasting glucose, hormone receptors, and expression of human epidermal growth factor receptor 2 (HER2). Extensively annotated specimens were obtained from 154 women with luminal B breast cancer diagnosed at two Italian comprehensive cancer centres. Participants' characteristics were descriptively analyzed overall and by HER2 status (positive vs. negative). BMI (<25 vs ≥25), pre-treatment fasting glucose (<median value of 94 mg/dl vs. ≥94) and percentage of hormone receptors were tested for association with HER2 expression in regression models. In univariate models, BMI, fasting glucose and, at a lesser extent, percentage of estrogen receptors (ER) were significantly and inversely associated with HER2 expression (OR: 0.32, 95% CI: 0.16-0.66; 0.43, 0.23-0.82; 0.96, 0.94-0.97, respectively). The multivariate models confirmed the protective role of BMI and ER on HER2 expression, with luminal B HER2 positive patients being significantly less frequent among women within the highest category of BMI and percentage expression of ER compared with their counterparts (OR: 0.22, 95% CI: 0.09-0.53; 0.95, 0.93-0.97). In conclusions, BMI and percentage of ER representation are inversely associated with HER2 expression in luminal B breast cancers. Upon confirmatory findings, this might help identify patient subgroups who may best benefit from the use of interventions targeting insulin resistance in well depicted breast cancer scenarios.

The effect of insulin resistance on breast cancer risk in Latinas of Mexican origin

BACKGROUND

Conclusive evidence has yet to emerge regarding the association between markers of hyperinsulinemia and breast cancer. We determined the effect of insulin resistance (IR) on breast cancer risk in Latinas of Mexican origin who did not have a direct family history of breast cancer and had not been previously diagnosed with prediabetes or diabetes.

METHODS

This was a case-control study in which a case (n=124) was defined as a patient with a recent histopathologic diagnosis of breast cancer and a control (n=197) was defined as a participant who had recently undergone a mammography and had either a Breast Imaging, Reporting & Data System (BI-RADS)-1 or a BI-RADS-2 score. Plasma glucose, insulin, and glycated hemoglobin (HbA1c) levels were measured. IR was determined by using the homeostasis model assessment (HOMA-IR) criterion. Odds ratios (OR) and 95% confidence intervals (CI) were determined using unconditional binary logistic regression analysis.

RESULTS

IR was detected in 33.9% of cases and 41.6% of controls, based on a HOMA-IR ≥3.5. Although multivariate analysis did not show any association between IR and breast cancer risk (OR 0.56, 95% CI 0.31-1.01), it showed that an HbA1c ≥5.7% increased the risk of breast cancer (OR 3.41, 95% CI 1.93-6.01), regardless of menopausal status.

CONCLUSIONS

The findings suggest that IR had no effect on breast cancer risk; however HbA1c increased the risk in Latinas of Mexican origin who had not been diagnosed previously with prediabetes or diabetes and had no direct family history of breast cancer. Prospective studies are required to establish the impact of IR over time.

CARING (CAncer Risk and INsulin analoGues): the association of diabetes mellitus and cancer risk with focus on possible determinants - a systematic review and a meta-analysis

Background:

Patients suffering from diabetes mellitus (DM) may experience an increased risk of cancer; however, it is not certain whether this effect is due to diabetes per se.

Objective:

To examine the association between DM and cancers by a systematic review and meta-analysis according to the PRISMA guidelines.

Data Sources:

The systematic literature search includes Medline at PubMed, Embase, Cinahl, Bibliotek.dk, Cochrane library, Web of Science and SveMed+ with the search terms: “Diabetes mellitus”, “Neoplasms”, and “Risk of cancer”.

Study Eligibility Criteria:

The included studies compared the risk of cancer in diabetic patients versus non-diabetic patients. All types of observational study designs were included.

Results:

Diabetes patients were at a substantially increased risk of liver (RR=2.1), and pancreas (RR=2.2) cancer. Modestly elevated significant risks were also found for ovary (RR=1.2), breast (RR=1.1), cervix (RR=1.3), endometrial (RR=1.4), several digestive tract (RR=1.1-1.5), kidney (RR=1.4), and bladder cancer (RR=1.1). The findings were similar for men and women, and unrelated to study design. Meta-regression analyses showed limited effect modification of body mass index, and possible effect modification of age, gender, with some influence of study characteristics (population source, cancer- and diabetes ascertainment).

Limitations:

Publication bias seemed to be present. Only published data were used in the analyses.

Conclusions:

The systematic review and meta-analysis confirm the previous results of increased cancer risk in diabetes and extend this to additional cancer sites. Physicians in contact with patients with diabetes should be aware that diabetes patients are at an increased risk of cancer.

Prediabetes, diabetes, and risk of breast cancer: a case-control study

BACKGROUND AND AIMS

Although underlying mechanisms have been described to account for the association between prediabetes and diabetes with breast cancer, reported results have been inconsistent. We undertook this study to determine whether prediabetes and diabetes are risk factors for breast cancer in Mexican women with no family history of breast cancer in the mother, daughters, or sisters.

METHODS

A case-control study was carried out during 2011-2013. "Case" referred to patients with a histopathological diagnosis of breast cancer (incident and primary cases) (n = 240); "controls" were those with a BI-RADS 1 or 2 mammography result (n = 406). Categorization of prediabetes and diabetes was based on self-reporting or fasting glucose and glycated hemoglobin blood sampling results. Reproductive and sociodemographic data were collected by interview. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated using multivariate unconditional binary logistic regression analysis.

RESULTS

Prediabetes increased the risk of breast cancer in postmenopausal women (adjusted OR 2.08, 95% CI 1.10-3.96) as did diabetes (adjusted OR 2.85, 95% CI 1.55-5.26). A history of diabetes preceding breast cancer by ≥7 years and <7 years were both associated with an increased risk for breast cancer (adjusted OR 2.80, 95% CI 1.40-5.60 and 3.00, 95% CI 1.50-5.90, respectively).

CONCLUSIONS

This is the first study in Mexico evaluating prediabetes and diabetes as breast cancer risk factors in women with no first-degree relatives with breast cancer. Our findings suggest that women with prediabetes and diabetes should be considered a more vulnerable population for early breast cancer detection.

Association between insulin resistance and breast carcinoma: a systematic review and meta-analysis

Objective

This study was undertaken to evaluate the association between components defining insulin resistance and breast cancer in women.

Study Design

We conducted a systematic review of four databases (PubMed-Medline, EMBASE, Web of Science, and Scopus) for observational studies evaluating components defining insulin resistance in women with and without breast cancer. A meta-analysis of the association between insulin resistance components and breast cancer was performed using random effects models.

Results

Twenty-two studies (n = 33,405) were selected. Fasting insulin levels were not different between women with and without breast cancer (standardized mean difference, SMD −0.03, 95%CI −0.32 to 0.27; p = 0.9). Similarly, non-fasting/fasting C-peptide levels were not different between the two groups (mean difference, MD 0.07, −0.21 to 0.34; p = 0.6). Using individual odds ratios (ORs) adjusted at least for age, there was no higher risk of breast cancer when upper quartiles were compared with the lowest quartile (Q1) of fasting insulin levels (OR _{Q2 vs. Q1} 0.96, 0.71 to 1.28; OR _{Q3 vs. Q1} 1.22, 0.91 to 1.64; OR _{Q4 vs. Q1} 0.98, 0.70 to 1.38). Likewise, there were no differences for quartiles of non-fasting/fasting C-peptide levels (OR _{Q2 vs. Q1} 1.12, 0.91 to 1.37; OR _{Q3 vs. Q1} 1.20, 0.91 to 1.59; OR _{Q4 vs. Q1} 1.40, 1.03 to 1.92). Homeostatic model assessment (HOMA-IR) levels in breast cancer patients were significantly higher than in people without breast cancer (MD 0.22, 0.13 to 0.31, p<0.00001).

Conclusions

Higher levels of fasting insulin or non-fasting/fasting C-peptide are not associated with breast cancer in women. HOMA-IR levels are slightly higher in women with breast cancer.

Hypertension and the risk of breast cancer in Chilean women: a case-control study

BACKGROUND

Breast cancer is the most common cancer in women worldwide. Although different metabolic factors have been implicated in breast cancer development, the relationship between hypertension and breast cancer has not been elucidated.

AIM

To evaluate hypertension as a risk factor for breast cancer in Chilean women of low and middle socio-economic status.

METHODS

We conducted an age-matched (1:1) case-control study in 3 hospitals in Santiago, Chile. Breast cancer cases (n=170) were histopathologically confirmed. Controls had been classified as Breast Imaging Reporting and Data System I (negative) or II (benign findings) within 6 months of recruitment. Blood pressure was measured using a mercury sphygmomanometer and standardized procedures. We used 2 hypertension cut-off points: blood pressures of ≥140/90 mmHg and ≥130/85 mmHg. Fasting insulin and glucose levels were assessed, and anthropometric, sociodemographic, and behavioral information were collected. Odds ratios and 95% confidence intervals were estimated for the entire sample and restricted to postmenopausal women using multivariable conditional logistic regression models.

RESULTS

Hypertension (≥140/90 mmHg) was significantly higher in cases (37.1%) than controls (17.1%) for the entire sample and in postmenopausal pairs (44.0% compared to 23.8%). In crude and adjusted models, hypertensive women had a 4-fold increased risk of breast cancer (adjusted odds ratio: 4.2; 95% confidence interval: 1.8; 9.6) compared to non-hypertensive women in the entire sample. We found a similar association in the postmenopausal group (adjusted odds ratio: 2.8; 95% confidence interval: 1.1; 7.4). A significant effect was also observed when hypertension was defined as blood pressure of ≥130/85 mmHg.

CONCLUSION

A significant association was found between hypertension and breast cancer over the entire sample and when restricted to postmenopausal women. Hypertension is highly prevalent in Latin America and may be a modifiable risk factor for breast cancer; therefore, a small association between hypertension and breast cancer may have broad implications.

Serum insulin and C-peptide concentration and breast cancer: a meta-analysis

PURPOSE

Chronic hyperinsulinemia may play a role in breast cancer etiology. We performed a meta-analysis examining whether serum concentrations of insulin and C-peptide are associated with increased breast cancer risk.

METHODS

We restricted our analyses to prospective studies. After a systematic literature search, we computed summary relative risks (SRRs) and 95 % confidence intervals (95 % CIs) using random effect models applied to the relative risk associated with the highest versus lowest quantile of serum concentrations. We also graphically examined results in order to identify whether dose-response relationships were present.

RESULTS

Six articles including 1,890 cases were retrieved for serum insulin levels and five for serum C-peptide levels including 1,759 cases. SRR and 95 % CI were 1.08 (0.66-1.78) for insulin and 1.04 (0.77-1.41) for C-peptide. Heterogeneity of results between studies was high for insulin and inexistent for C-peptide. Restricting the analysis to women diagnosed with breast cancer before or after menopause did not alter results. In insulin studies, SRR computed from relative risks not adjusted for body mass index (and other risk factors) was 1.22 (0.91-1.63). The SRR fell to 1.02 (0.53-1.97) in studies that adjusted for body mass index and other factors. Similar drops occurred in C-peptide studies, from 1.11 (0.87-1.41) to 1.06 (0.70-1.61). No consistent dose-response relationship was apparent in either pre- or post-menopausal cancers.

CONCLUSIONS

Our meta-analysis of observational studies found no evidence of an association between serum insulin or C-peptide concentrations and breast cancer risk. Increased risk found by some studies may have been due to inadequate control for adiposity.

Diabetes increases the risk of breast cancer: a meta-analysis

The aim of this meta-analysis was to collate and analyse all primary observational studies investigating the risk of breast cancer (BC) associated with diabetes. In addition, we aimed to complete subgroup analyses by both type of diabetes and gender of study participants to further clarify the origin of any such association between the two. Studies were obtained from a database search of MEDLINE, EMBASE, PubMed, Current Contents Connect and Google Scholar with additional cross-checking of reference lists. Collated data were assessed for heterogeneity and a pooled odds ratio (OR) calculated. Forty-three studies were included in the meta-analysis with 40 studies investigating BC in women and six studies investigating BC in men. Overall, we found a significantly increased risk of BC associated with diabetes in women (OR 1.20, 95% confidence interval (CI) 1.13-1.29). After subgroup analysis by type of diabetes, the association was unchanged with type 2 diabetes (OR 1.22, 95% CI 1.07-1.40) and nullified with gestational diabetes (OR 1.06, 95% CI 0.79-1.40). There were insufficient studies to calculate a pooled OR of the risk of BC associated with type 1 diabetes. There was an increased risk of BC in males with diabetes mellitus; however, the results did not reach statistical significance (OR 1.29, 95% CI 0.99-1.67). In conclusion, diabetes increases the risk of BC in women. This association is confirmed in women with type 2 diabetes and supports the hypothesis that diabetes is an independent risk factor for BC.

Diabetes and breast cancer risk: a meta-analysis

Background:

The potential of an increased risk of breast cancer in women with diabetes has been the subject of a great deal of recent research.

Methods:

A meta-analysis was undertaken using a random effects model to investigate the association between diabetes and breast cancer risk.

Results:

Thirty-nine independent risk estimates were available from observational epidemiological studies. The summary relative risk (SRR) for breast cancer in women with diabetes was 1.27 (95% confidence interval (CI), 1.16–1.39) with no evidence of publication bias. Prospective studies showed a lower risk (SRR 1.23 (95% CI, 1.12–1.35)) than retrospective studies (SRR 1.36 (95% CI, 1.13–1.63)). Type 1 diabetes, or diabetes in pre-menopausal women, were not associated with risk of breast cancer (SRR 1.00 (95% CI, 0.74–1.35) and SRR 0.86 (95% CI, 0.66–1.12), respectively). Studies adjusting for body mass index (BMI) showed lower estimates (SRR 1.16 (95% CI, 1.08–1.24)) as compared with those studies that were not adjusted for BMI (SRR 1.33 (95% CI, 1.18–1.51)).

Conclusion:

The risk of breast cancer in women with type 2 diabetes is increased by 27%, a figure that decreased to 16% after adjustment for BMI. No increased risk was seen for women at pre-menopausal ages or with type 1 diabetes.

Cancer risk associated with use of metformin and sulfonylurea in type 2 diabetes: a meta-analysis

OBJECTIVE

Oral antidiabetic drugs (including metformin and sulfonylurea) may play a role in the relationship between type 2 diabetes and cancer. To quantify the association between metformin and sulfonylurea and the risk of cancer, we performed a meta-analysis of available studies on the issue.

MATERIALS AND METHODS

We performed a MEDLINE search for observational studies that investigated the risk of all cancers and specific cancer sites in relation to use of metformin and/or sulfonylurea among patients with type 2 diabetes mellitus. Fixed- and random-effect models were fitted to estimate the summary relative risk (RR). Between-study heterogeneity was tested using χ(2) statistics and measured with the I(2) statistic. Publication bias was evaluated using funnel plot and Egger's regression asymmetry test.

RESULTS

Seventeen studies satisfying inclusion criteria and including 37,632 cancers were evaluated after reviewing 401 citations. Use of metformin was associated with significantly decreased RR of all cancers (summary RR 0.61, 95% confidence interval [CI] 0.54-0.70), colorectal cancer (0.64, 95% CI 0.54-0.76), and pancreatic cancer (0.38, 95% CI 0.14-0.91). With the exception of colorectal cancer, significant between-study heterogeneity was observed. Evidence of publication bias for metformin-cancer association was also observed. There was no evidence that metformin affects the risk of breast and prostate cancers, nor that sulfonylurea affects the risk of cancer at any site.

CONCLUSIONS

Metformin, but not sulfonylurea, appears to reduce subsequent cancer risk. This has relevant implications in light of the exploding global epidemic of diabetes.

Metabolic syndrome and incidence of liver and breast cancers in Japan

AIM OF THE STUDY

To clarify the relationship between the presence of metabolic syndrome and the incidence of cancer in a general Japanese population.

METHODS

A retrospective cohort study was conducted among 8329 male and 15,386 female subjects between 1992 and 2000. The analysis used five definitions of metabolic syndrome. The information on the site-specific cancer was obtained from the population-based cancer registry. A Cox proportional hazard model was adapted for the statistical analyses. The average follow-up period was 9.1 years.

RESULTS

The National Cholesterol Education Program Adult Treatment Panel III 2001 criteria of metabolic syndrome revealed that the hazard ratio of metabolic syndrome for liver cancer was 1.89 (95% confidence interval (CI) 1.11-3.22) for males, and 3.67 (CI 1.78-7.57) for females. The hazard ratio for female breast cancer was 2.87 (CI 1.67-4.94). When the analysis was limited to postmenopausal women (55 years of age or older), the ratio increased to 6.73 (CI 2.93-15.43). The NCEP-ATPIII 2001 criteria were superior to the other four proposed criteria for predicting the incidence of cancer. In the statistical model, which included all components of the metabolic syndrome and the metabolic syndrome (present or absent), high blood glucose was a significant associated factor for all sites and liver cancers, whereas the metabolic syndrome was found to be a significant associated factor for breast cancer.

CONCLUSION

Metabolic syndrome may play an important role in the incidence of breast cancer. High fasting plasma glucose level is considered to be useful as an associated factor for the incidence of all-sites and liver cancer.

Metformin and cancer risk in diabetic patients: a systematic review and meta-analysis

Metformin, an insulin-lowering agent, has been associated with decreased cancer risk in epidemiologic studies in diabetic patients. We performed a comprehensive literature search and meta-analysis of epidemiologic studies to assess the effect of metformin on cancer incidence and mortality in diabetic patients, using Pubmed, ISI Web of Science, Embase, and the Cochrane library until May 2009, with no language or time restrictions. Independent reports with sufficient information to allow risk estimation of cancer risk/mortality and a measure of uncertainty were reviewed and cross-checked independently by three investigators. Eleven studies were selected for relevance in terms of intervention, population studied, independence, and reporting of cancer incidence or mortality data, reporting 4,042 cancer events and 529 cancer deaths. A 31% reduction in overall summary relative risk (0.69; 95% confidence interval, 0.61-0.79) was found in subjects taking metformin compared with other antidiabetic drugs. The inverse association was significant for pancreatic and hepatocellular cancer, and nonsignificant for colon, breast, and prostate cancer. A trend to a dose-response relationship was noted. Metformin is associated with a decreased risk of cancer incidence compared with other treatments among diabetic patients. Given the retrospective nature of most studies and the possibility that the control treatments increase risk, phase II trials are needed before large cancer prevention trials are launched.

New users of metformin are at low risk of incident cancer: a cohort study among people with type 2 diabetes

OBJECTIVE

The antidiabetic properties of metformin are mediated through its ability to activate the AMP-activated protein kinase (AMPK). Activation of AMPK can suppress tumor formation and inhibit cell growth in addition to lowering blood glucose levels. We tested the hypothesis that metformin reduces the risk of cancer in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

In an observational cohort study using record-linkage databases and based in Tayside, Scotland, U.K., we identified people with type 2 diabetes who were new users of metformin in 1994-2003. We also identified a set of diabetic comparators, individually matched to the metformin users by year of diabetes diagnosis, who had never used metformin. In a survival analysis we calculated hazard ratios for diagnosis of cancer, adjusted for baseline characteristics of the two groups using Cox regression.

RESULTS

Cancer was diagnosed among 7.3% of 4,085 metformin users compared with 11.6% of 4,085 comparators, with median times to cancer of 3.5 and 2.6 years, respectively (P < 0.001). The unadjusted hazard ratio (95% CI) for cancer was 0.46 (0.40-0.53). After adjusting for sex, age, BMI, A1C, deprivation, smoking, and other drug use, there was still a significantly reduced risk of cancer associated with metformin: 0.63 (0.53-0.75).

CONCLUSIONS

These results suggest that metformin use may be associated with a reduced risk of cancer. A randomized trial is needed to assess whether metformin is protective in a population at high risk for cancer.

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.

Insulin resistance, obesity and breast cancer risk

Breast cancer (BC) is one of the most important problems of public health. Among the avoidable risk factors during a woman's life, overweight and obesity are very important ones. Furthermore they are increasing worldwide. The risk of breast cancer is traditionally linked to obesity in postmenopausal women; conversely, it is neutral or even protective in premenopausal women. Since the initiator and promoter factors for BC act over a long time, it seems unlikely that the menopausal transition may have too big an impact on the role of obesity in the magnitude of the risk. We reviewed the literature in an attempt to understand this paradox, with particular attention to the body fat distribution and its impact on insulin resistance. The association of insulin resistance and obesity with BC risk are biologically plausible and consistent. Estradiol (E2) and IGFs act as mitogens in breast cancer cells. They act together and reciprocally. However the clinical and biological methods to assess the impact of insulin resistance are not always accurate. Furthermore insulin resistance is far from being a constant feature in obesity, particularly in premenopausal women; this complicates the analysis and explains the discrepancies in large prospective trials. The most consistent clinical feature to assess risk across epidemiological studies seems to be weight gain during lifetime. Loss of weight is associated with a lower risk for postmenopausal BC compared with weight maintenance. This observation should be an encouragement for women since loss of weight may be an effective strategy for breast cancer risk reduction.