Associations between leptin and adiponectin receptor upregulation, visceral obesity and tumour stage in oesophageal and junctional adenocarcinoma

Advances in biomarkers for esophageal cancer

Cancer of the esophagus is an aggressive disease with early lymphatic and hematogenous dissemination and at present often considered as one clinical entity because of their comparable increasing incidence, prognosis and optimal treatment options. However, it is still a matter of debate whether these malignancies have the same pathogenesis and genotype. Despite recent advances, treatment of upper gastrointestinal malignancies remains a significant challenge. Molecular pathology has revealed many molecular mechanisms of disease progression, which are related to prognosis. Better knowledge of molecular bases may lead to new paradigms, improved prognostication, early diagnosis and individually tailored therapeutic options. This review summarizes the rationale, preclinical evidence, retrospective clinical analyses and the interim clinical data pertaining HER2 therapy and many other molecular pathways.

The esophagitis to adenocarcinoma sequence; the role of inflammation

Esophageal adenocarcinoma (EAC) is the eighth most common cancer worldwide, and approximately 15% of patients survive 5years. Reflux disease (GERD) and Barrett's esophagus (BE) are major risk factors for the development of EAC, and epidemiologic studies highlight a strong association with obesity. The immune, inflammatory and intracellular signaling changes resulting from chronic inflammation of the esophageal squamous epithelium are increasingly well characterized. In GERD and Barrett's, an essential role for T-cells in the initiation of inflammation in the esophagus has been identified, and a balance between T-cell responses and phenotype may play an important role in disease progression. Obesity is a chronic low-grade inflammatory state, fueled by adipose tissue derived- inflammatory mediators such as IL-6, TNF-α and leptin, representing a novel area for targeted research. Additionally, reactive oxygen species (ROS) and receptor tyrosine kinase (RTK) activation may drive progression from esophagitis to EAC, and downstream signaling pathways employed by these molecules may be important. This review will explain the diverse range of mechanisms potentially driving and maintaining inflammation within the esophagus and explore both existing and future therapeutic strategies targeting the process.

Expression and biologic significance of adiponectin receptors in papillary thyroid carcinoma

Obesity is associated with a higher incidence of thyroid cancer. Adiponectin is one of the most abundant adipokines with a pleiotropic role in metabolism and in the development and progression of cancer. It has been shown that circulating adiponectin level is inversely associated with the risk of thyroid cancer. This study aimed to investigate the possible association between the expression of adiponectin receptors (AdipoR1 and AdipoR2) and clinicopathological variables in papillary thyroid cancer. We found that protein levels of AdipoR1 and AdipoR2 were increased in some thyroid cancer specimens compared with adjacent normal thyroid tissues. Thyroid cancer cells expressed AdipoR1 and AdipoR2, which were attenuated by histone deacetylase inhibitors valproic acid and trichostatin A. Adiponectin stimulated AMP-activated protein kinase phosphorylation in thyroid cancer cells. We further determined the expression of AdipoR1 and AdipoR2 by immunohistochemical staining in primary tumor samples and metastatic lymph nodes. AdipoR1 was expressed in 27 % of primary tumors and AdipoR2 in 47 %. Negative expression of both adiponectin receptors was significantly associated with extrathyroidal invasion, multicentricity, and higher TNM stage. There was a trend toward decreased disease-free survival in patients with negative tumor expression of AdipoR1 and AdipoR2 (log-rank P = 0.051). Collectively, overexpression of adiponectin receptors was observed in some tumor tissues of papillary thyroid cancer and was associated with a better prognosis.

Association between markers of obesity and progression from Barrett's esophagus to esophageal adenocarcinoma

BACKGROUND & AIMS

Individuals with Barrett's esophagus (BE) have an increased risk of developing esophageal adenocarcinoma (EA). Obesity contributes to the development of BE and its progression to cancer. We investigated the roles of obesity-induced hyperinsulinemia and dysregulation of adipokines in these processes.

METHODS

We measured fasting levels of glucose, insulin, leptin, and adiponectin in 392 patients enrolled in the Seattle Barrett's Esophagus Study. We calculated homeostatic model assessment scores (a measure of insulin sensitivity) and identified subjects with metabolic syndrome. We evaluated the association between these measures and the risk of EA using Cox regression models adjusted for known risk factors.

RESULTS

Increasing homeostatic model assessment scores were associated with an increasing risk for EA; the strongest association was observed within the first 3 years after participants entered the study (hazard ratio [HR], 2.45; 95% confidence interval [CI], 1.43-4.1; P trend = .001). Leptin level also was associated significantly with an increased risk of EA within 3 years (HR, 2.51; 95% CI, 1.09-5.81; P trend = .03) and 6 years (HR, 2.07; 95% CI, 1.01-4.26; P trend = .048) of baseline. The level of high-molecular-weight adiponectin had a nonlinear inverse association with risk of EA; the strongest associations were observed in the second tertile (HR, 0.34; 95% CI, 0.14-0.82). Metabolic syndrome was not associated with risk of EA.

CONCLUSIONS

Among patients with BE, increased levels of leptin and insulin resistance are associated with increased risk for EA, whereas increased levels of high-molecular-weight adiponectin is associated inversely with EA. These biomarkers might be used to determine cancer risk among patients with BE.

The role of chronic inflammation in obesity-associated cancers

There is a strong relationship between metabolism and immunity, which can become deleterious under conditions of metabolic stress. Obesity, considered a chronic inflammatory disease, is one example of this link. Chronic inflammation is increasingly being recognized as an etiology in several cancers, particularly those of epithelial origin, and therefore a potential link between obesity and cancer. In this review, the connection between the different factors that can lead to the chronic inflammatory state in the obese individual, as well as their effect in tumorigenesis, is addressed. Furthermore, the association between obesity, inflammation, and esophageal, liver, colon, postmenopausal breast, and endometrial cancers is discussed.

Barrett's esophagus in 2012: updates in pathogenesis, treatment, and surveillance

Barrett's esophagus (BE) is the only established precursor lesion in the development of esophageal adenocarcinoma (EAC) and it increases the risk of cancer by 11-fold. It is regarded as a complication of gastroesophageal reflux disease. There is an ever-increasing body of knowledge on the pathogenesis, diagnosis, treatment, and surveillance of BE and its associated dysplasia. In this review, we summarize the latest advances in BE research and clinical practice in the past 2 years. It is critical to understand the molecular underpinnings of this disorder to comprehend the clinical outcomes of the disease. For clinical gastroenterologists, there is also continuous growth of endoscopic approaches which is daunting, and further improvements in the detection and treatment of BE and early EAC are anticipated. In the future, we may see the increased role of biomarkers, both molecular and imaging, in both diagnostic and therapeutic strategies for BE.

Adiponectin receptor expression in gastric carcinoma: implications in tumor development and progression

PURPOSE

Adiponectin, an adipocyte-secreted endogenous insulin sensitizer, appears to play an important role in progression of several malignancies. Expression of adiponectin receptors--AdipoR1 and AdipoR2--has been documented in gastric cancer (GC) cell lines, but its role in GCs is still controversial. We investigated expression level of 2 adiponectin receptors and correlated their expression with prognosis in GC patients.

METHODS

We immunohistochemically evaluated AdipoR1 and AdipoR2 expression in 59 non-neoplastic gastric mucosas, 48 gastric adenomas, 250 GCs, and 58 lymph nodes involved by metastatic GC and assessed its association with clinicopathologic characteristics.

RESULTS

Expression rates of both receptors increased stepwise in non-neoplastic gastric mucosa, gastric adenoma, intestinal-type GC, and metastatic GC (p < 0.001). AdipoR1 and AdipoR2 expression was observed in 85 (34.0 %) and 118 (47.2 %) GC cases, respectively. Expression rates were higher in intestinal-type GC than in diffuse-type GC (p < 0.001 and 0.016, respectively). AdipoR1 and AdipoR2 expression was more frequent in advanced GC than in early GC (p < 0.001, each) and was associated with lymphatic invasion (p = 0.046 and 0.001, respectively). AdipoR2 expression was associated with poor overall and disease-free survival (p = 0.001 and 0.007, respectively). AdipoR1 expression was associated with poor disease-free survival for intestinal-type GC patients (p = 0.046). In multivariate analysis, AdipoR2 was an independent prognostic factor for intestinal-type GC (p = 0.017).

CONCLUSIONS

Adiponectin receptor expression is related to GC development and progression, especially intestinal-type GC. Thus, adiponectin receptor expression can serve as a prognostic marker in GC patients.

Overweight patients operated on for cancer of the esophagus survive longer than normal-weight patients

BACKGROUND

Esophageal adenocarcinoma is often associated with obesity, and a 5 Kg m(-2) increase in body mass index (BMI) has, in fact, been found to be strongly associated with the risk of this type of cancer (RR, 1.52; p < 0.0001). Esophagectomy with lymphoadenectomy is the mainstay of therapy for these patients. The aim of this study was to assess and compare the surgical and oncological outcomes as well as the survival rates of underweight, normal weight, overweight, and obese patients following esophagectomy for esophageal cancer.

PATIENTS AND METHODS

Data relative to 1,127 patients with esophageal adenocarcinoma presenting at a specialized tertiary hospital (the Center of Esophageal Diseases for the Veneto Region) between 2000 and 2008 were prospectively collected. The 278 subjects whose BMI values before disease onset were available and underwent esophagectomy were enrolled in the study. Sixty-one of the 278 patients were classified as obese (BMI >30), 121 were classified as overweight (BMI, 25-29.9), 81 were classified as normal weight (BMI <24.9), and 15 ones as underweight (BMI <20). The outcome and survival of the four groups were compared. Frequency and survival analyses were carried out.

RESULTS

The rate of R0 esophagectomy and the incidence of toxicity during neoadjuvant chemotherapy were similar in the four groups. Respiratory complications after R0 esophagectomy seemed to be more frequent in the underweight and normal-weight patients group (p < 0.01). Moreover, underweight patients had a significantly higher rate of septic, cardiovascular, and metabolic postoperative complications. The 121 overweight patients had a better overall survival rate compared to normal weight and obese patients (p = 0.05). This difference was not significant if patients were stratified in stages I or II or stages III or IV.

CONCLUSION

Overweight patients seem to respond better to esophageal cancer and esophagectomy with respect to normal-weight ones. This data seem to suggest that in spite of several unfavorable features, a moderate increase of weight may be helpful to survive after esophagectomy for cancer.

Metabolic syndrome, obesity, and gastrointestinal cancer

METABOLIC SYNDROME IS A CLUSTER OF METABOLIC ABNORMALITIES AND IS DEFINED AS THE PRESENCE OF THREE OR MORE OF THE FOLLOWING FACTORS: increased waist circumference, elevated triglycerides, low high-density lipoprotein cholesterol, high blood pressure, and high fasting glucose. Obesity, which is accompanied by metabolic dysregulation often manifested in the metabolic syndrome, is an established risk factor for many cancers. Adipose tissue, particularly visceral fat, is an important metabolic tissue as it secretes systemic factors that alter the immunologic, metabolic, and endocrine milieu and also promotes insulin resistance. Within the growth-promoting, proinflammatory environment of the obese state, cross-talk between macrophages, adipocytes, and epithelial cells occurs via obesity-associated hormones, adipocytokines, and other mediators that may enhance cancer risk and progression. This paper synthesizes the evidence on key molecular mechanisms underlying the obesity-cancer link.

Progress in understanding the relationship between adiponectin receptors R1&R2 and carcinomas

Adiponectin is a key hormone secreted by adipocytes. It is involved in glucose and lipid metabolism and insulin sensitization, and has anti-inflammatory, anti-arteriosclerosis and anti-carcinogenic effects. Many studies have found that adiponectin is related to coronary heart disease, type 2 diabetes mellitus, hypertension and cancer. Recently, adiponectin receptors R1 and R2 have been reported to be expressed in several malignancies, such as colorectal cancer, breast cancer, endometrial cancer, esophageal cancer, gastric cancer, prostate cancer and nephrocyte cancer.

Expression of adiponectin receptors R1 and R2 in colorectal carcinoma and colorectal adenoma

AIM: To investigate the relationship between expression of adiponectin receptors R1 and R2 and clinicopathological parameters in colorectal cancer and colorectal adenomas.

METHODS: Expression of adiponectin receptors R1 and R2 in surgical specimens of colorectal carcinoma (n = 51), colorectal adenomas (n = 42), and normal colorectal mucosa (n = 35) was detected by immunohistochemistry.

RESULTS: The expression of adiponectin receptors R1 and R2 was significantly higher in colorectal carcinoma than in colorectal adenomas (P = 0.047, 0.035), and in colorectal adenomas than in normal colorectal mucosa (P = 0.042, 0.046). Expression of adiponectin receptors was significantly correlated with histological differentiation, lymph node metastasis, and TNM stages (all P < 0.05), but not with other clinicopathological features including sex, age, tumor size.

CONCLUSION: Adiponectin receptors R1 and R2 are expressed in both colorectal carcinoma and normal colorectal mucosa. Expression of adiponectin receptors R1 and R2 is enhanced in colorectal cancer and adenomas. Adiponectin receptor expression closely correlates with tumor differentiation, lymph node metastasis and TNM stage in patients with colorectal cancer. Adiponectin receptors may become new targets for colorectal cancer treatment.

The association between obesity factor and esophageal caner

Accumulating epidemiological studies have supported the link between increased body mass index, central obesity and esophageal adenocarcinoma. This association appears stronger than that for other types of obesity-related cancers. Central obesity or visceral fat, more often observed in men, is much more strongly associated with adenocarcinoma than body mass index alone, possibly contributing to the imbalance of disease occurrence between the sexes. Potential mechanisms underlying the association between obesity and esophageal adenocarcinoma have been recently identified, including the insulin-like growth factor pathway, adipokines and sex hormone disturbances. These findings are summarized in this review; however, more research is warranted before these mechanisms are conclusively established.

The role of adiponectin in cancer: a review of current evidence

Excess body weight is associated not only with an increased risk of type 2 diabetes and cardiovascular disease (CVD) but also with various types of malignancies. Adiponectin, the most abundant protein secreted by adipose tissue, exhibits insulin-sensitizing, antiinflammatory, antiatherogenic, proapoptotic, and antiproliferative properties. Circulating adiponectin levels, which are determined predominantly by genetic factors, diet, physical activity, and abdominal adiposity, are decreased in patients with diabetes, CVD, and several obesity-associated cancers. Also, adiponectin levels are inversely associated with the risk of developing diabetes, CVD, and several malignancies later in life. Many cancer cell lines express adiponectin receptors, and adiponectin in vitro limits cell proliferation and induces apoptosis. Recent in vitro studies demonstrate the antiangiogenic and tumor growth-limiting properties of adiponectin. Studies in both animals and humans have investigated adiponectin and adiponectin receptor regulation and expression in several cancers. Current evidence supports a role of adiponectin as a novel risk factor and potential diagnostic and prognostic biomarker in cancer. In addition, either adiponectin per se or medications that increase adiponectin levels or up-regulate signaling pathways downstream of adiponectin may prove to be useful anticancer agents. This review presents the role of adiponectin in carcinogenesis and cancer progression and examines the pathophysiological mechanisms that underlie the association between adiponectin and malignancy in the context of a dysfunctional adipose tissue in obesity. Understanding of these mechanisms may be important for the development of preventive and therapeutic strategies against obesity-associated malignancies.

Dietary intake of lignans and risk of adenocarcinoma of the esophagus and gastroesophageal junction

PURPOSE

The strong male predominance in esophageal and gastroesophageal junctional adenocarcinoma remains unexplained. Sex hormonal influence has been suggested, but not proven. A protective role of dietary phytoestrogen lignans was hypothesized.

METHODS

A Swedish nationwide population-based case-control study was conducted in 1995-1997, including 181 cases of esophageal adenocarcinoma, 255 cases of gastroesophageal junctional adenocarcinoma, 158 cases of esophageal squamous cell carcinoma, and 806 control subjects. Data on various exposures, including dietary data, were collected through personal interviews and questionnaires. Dietary intake of lignans was assessed using a food frequency questionnaire and categorized into quartiles based on the consumption among the control participants. Unconditional logistic regression was used to calculate odds ratios (ORs) with 95 % confidence intervals (CIs), including adjustment for all established risk factors.

RESULTS

Participants in the highest quartile of intake of lignans compared with the lowest quartile were at a decreased risk of esophageal adenocarcinoma (OR, 0.65; 95 % CI, 0.38-1.12; p for trend =0.03), gastroesophageal junctional adenocarcinoma (OR, 0.37; 95 % CI, 0.23-0.58; p for trend <0.0001), and these adenocarcinomas combined (OR, 0.45; 95 % CI, 0.31-0.67; p for trend <0.0001). No clear associations were found between lignan intake and risk of esophageal squamous cell carcinoma.

CONCLUSIONS

This population-based study indicates that a high dietary intake of lignans decreases the risk of adenocarcinoma of the esophagus and gastroesophageal junction.

Estrogen, male dominance and esophageal adenocarcinoma: is there a link?

Esophageal adenocarcinoma is a cancer with poor prognosis, and its incidence has risen sharply over recent decades. Obesity is a major risk factor for developing this cancer and there is a clear male gender bias in the incidence that cannot be fully explained by known risk factors. It is possible that a difference in the expression of estrogen, or its signaling axes, may contribute to this gender bias. We undertook a comprehensive literature search and analyzed the available data regarding estrogen and estrogen receptor expression, and the possible sex-specific links with esophageal adenocarcinoma development. Potentially relevant associations between visceral vs subcutaneous fat deposition and estrogen expression, and the effect of crosstalk between estrogen and leptin signaling were identified. We also found limited studies suggesting a role for estrogen receptor β expression in esophageal adenocarcinoma development. The current literature supports speculation on an etiological role for estrogen in the male gender bias in esophageal adenocarcinoma, but further studies are required.

Oncogenic role and therapeutic target of leptin signaling in breast cancer and cancer stem cells

Significant correlations between obesity and incidence of various cancers have been reported. Obesity, considered a mild inflammatory process, is characterized by a high level of secretion of several cytokines from adipose tissue. These molecules have disparate effects, which could be relevant to cancer development. Among the inflammatory molecules, leptin, mainly produced by adipose tissue and overexpressed with its receptor (Ob-R) in cancer cells is the most studied adipokine. Mutations of leptin or Ob-R genes associated with obesity or cancer are rarely found. However, leptin is an anti-apoptotic molecule in many cell types, and its central roles in obesity-related cancers are based on its pro-angiogenic, pro-inflammatory and mitogenic actions. Notably, these leptin actions are commonly reinforced through entangled crosstalk with multiple oncogenes, cytokines and growth factors. Leptin-induced signals comprise several pathways commonly triggered by many cytokines (i.e., canonical: JAK2/STAT; MAPK/ERK1/2 and PI-3K/AKT1 and, non-canonical signaling pathways: PKC, JNK and p38 MAP kinase). Each of these leptin-induced signals is essential to its biological effects on food intake, energy balance, adiposity, immune and endocrine systems, as well as oncogenesis. This review is mainly focused on the current knowledge of the oncogenic role of leptin in breast cancer. Additionally, leptin pro-angiogenic molecular mechanisms and its potential role in breast cancer stem cells will be reviewed. Strict biunivocal binding-affinity and activation of leptin/Ob-R complex makes it a unique molecular target for prevention and treatment of breast cancer, particularly in obesity contexts.

Oncogenic role and therapeutic target of leptin signaling in breast cancer and cancer stem cells

Significant correlations between obesity and incidence of various cancers have been reported. Obesity, considered a mild inflammatory process, is characterized by a high level of secretion of several cytokines from adipose tissue. These molecules have disparate effects, which could be relevant to cancer development. Among the inflammatory molecules, leptin, mainly produced by adipose tissue and overexpressed with its receptor (Ob-R) in cancer cells is the most studied adipokine. Mutations of leptin or Ob-R genes associated with obesity or cancer are rarely found. However, leptin is an anti-apoptotic molecule in many cell types, and its central roles in obesity-related cancers are based on its pro-angiogenic, pro-inflammatory and mitogenic actions. Notably, these leptin actions are commonly reinforced through entangled crosstalk with multiple oncogenes, cytokines and growth factors. Leptin-induced signals comprise several pathways commonly triggered by many cytokines (i.e., canonical: JAK2/STAT; MAPK/ERK1/2 and PI-3K/AKT1 and, non-canonical signaling pathways: PKC, JNK and p38 MAP kinase). Each of these leptin-induced signals is essential to its biological effects on food intake, energy balance, adiposity, immune and endocrine systems, as well as oncogenesis. This review is mainly focused on the current knowledge of the oncogenic role of leptin in breast cancer. Additionally, leptin pro-angiogenic molecular mechanisms and its potential role in breast cancer stem cells will be reviewed. Strict biunivocal binding-affinity and activation of leptin/Ob-R complex makes it a unique molecular target for prevention and treatment of breast cancer, particularly in obesity contexts.

Patients with high body mass index tend to have lower stage of esophageal carcinoma at diagnosis

High body mass index (H-BMI; ≥25 kg/m(2) ) is common in US adults. In a small cohort of esophageal cancer (EC) patients treated with surgery, H-BMI and diagnosis of early stage EC appeared associated. We evaluated a much larger cohort of EC patients. From a prospectively maintained database, we analyzed 925 EC patients who had surgery with or without adjunctive therapy. Various statistical methods were used. Among 925 patients, 69% had H-BMI, and 31% had normal body mass index (<25 kg/m(2) ; N-BMI). H-BMI was associated with men (P<0.001), Caucasians (P=0.064; trend), lower esophageal localization (P<0.001), adenocarcinoma histology (P<0.001), low baseline cT-stage (P=0.003), low baseline overall clinical stage (P=0.003), coronary artery disease (P=0.036), and diabetes (P<0.001). N-BMI was associated with weight loss (P<0.001), alcohol abuse (P=0.056; trend), ever/current smoking (P=0.014), and baseline cN+ (P=0.018). H-BMI patients with cT1 tumors (n=110) had significantly higher rates of gastresophageal reflux disease symptoms (P<0.001), gastresophageal reflux disease history (P<0.001), and Barrett's esophagus history (P<0.001) compared with H-BMI patients with cT2 tumors (n=114). Median survival of N-BMI patients was 36.66 months compared with 53.20 months for H-BMI patients (P=0.005). In multivariate analysis, older age (P<0.001), squamous histology (P=0.002), smoking (P=0.040), weight loss (P=0.002), high baseline stage (P<0.001), high number of ypN+ (P=0.005), high surgical stage (P<0.001), and American Society of Anesthesia scores, three out of four (P<0.001) were independent prognosticators for poor overall survival. We were able to perform propensity-based analysis of surgical complications between H-BMI and N-BMI patients. A comparison of fully matched 376 patients (188 with H-BMI and 188 with N-BMI) found no significant differences in the rate of complications between the two groups. This larger data set confirms that a fraction of H-BMI patients with antecedent history is diagnosed with early baseline EC. Upon validation of our data in an independent cohort, refinements in surveillance of symptomatic H-BMI patients are warranted and could be implemented. Our data also suggest that H-BMI patients do not experience higher rate of surgical complications compared with N-BMI patients.

Multiple signal pathways in obesity-associated cancer

Obesity is increasing worldwide and reaches to a large proportion of the population in developed countries. Thus, obesity-associated cancer has become a major health problem. Multiple cancer risk factors in obesity have been identified including insulin/insulin-like growth factor axis, adipokines and cytokines; and multiple intracellular signal pathways have been studied. However, the role of each signal pathway in obesity-associated cancer is controversial. In this review, the recent studies on signal pathways in obesity-associated cancer are summarized and a unified explanation is provided. Multiple risk factors could initially activate phosphoinositide 3-kinase (PI3K/Akt), mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) pathways. With increased severity of obesity, mammalian target of rapamycin (mTOR), which is down-stream of both PI3K/Akt and MAPK, is highly activated. Activated mTOR in turn inhibits the PI3K/Akt pathway and further activates the STAT3 pathway. This may explain the activation of the PI3K/Akt pathway at the early stage of obesity and its inhibition at the later stage. mTOR inhibition may be used for cancer therapy, but it may be necessary to be combined with the PI3K/Akt inhibitor as decreased mTOR activity will release its feedback inhibition on the PI3K/Akt pathway, which is under the influence of multiple cancer risk factors in obesity. Thus, dual inhibitors of PI3K and mTOR may provide a novel approach.

Visceral obesity, metabolic syndrome, insulin resistance and cancer

This paper presents emerging evidence linking visceral adiposity and the metabolic syndrome (MetSyn) with carcinogenesis. The link between obesity and cancer has been clearly identified in a multitude of robust epidemiological studies. Research is now focusing on the role of visceral adipose tissue in carcinogenesis; as it is recognised as an important metabolic tissue that secretes factors that systemically alter the immunological, metabolic and endocrine milieu. Excess visceral adipose tissue gives rise to a state of chronic systemic inflammation with associated insulin resistance and dysmetabolism, collectively known as the MetSyn. Prospective cohort studies have shown associations between visceral adiposity, the MetSyn and increased risk of breast cancer, colorectal cancer and oesophageal adenocarcinoma. Furthermore, visceral adiposity and the MetSyn have been associated with increased tumour progression and reduced survival. The mechanisms by which visceral adiposity and the MetSyn are thought to promote tumorigenesis are manifold. These include alterations in adipokine secretion and cell signalling pathways. In addition, hyperinsulinaemia, subsequent insulin resistance and stimulation of the insulin-like growth factor-1 axis have all been linked with visceral adiposity and promote tumour progression. Furthermore, the abundance of inflammatory cells in visceral adipose tissue, including macrophages and T-cells, create systemic inflammation and a pro-tumorigenic environment. It is clear from current research that excess visceral adiposity and associated dysmetabolism play a central role in the pathogenesis of certain cancer types. Further research is required to elucidate the exact mechanisms at play and identify potential targets for intervention.

Visceral adiposity, insulin resistance and cancer risk

BACKGROUND

There is a well established link between obesity and cancer. Emerging research is characterising this relationship further and delineating the specific role of excess visceral adiposity, as opposed to simple obesity, in promoting tumorigenesis. This review summarises the evidence from an epidemiological and pathophysiological perspective.

METHODS

Relevant medical literature was identified from searches of PubMed and references cited in appropriate articles identified. Selection of articles was based on peer review, journal and relevance.

RESULTS

Numerous epidemiological studies consistently identify increased risk of developing carcinoma in the obese. Adipose tissue, particularly viscerally located fat, is metabolically active and exerts systemic endocrine effects. Putative pathophysiological mechanisms linking obesity and carcinogenesis include the paracrine effects of adipose tissue and systemic alterations associated with obesity. Systemic changes in the obese state include chronic inflammation and alterations in adipokines and sex steroids. Insulin and the insulin-like growth factor axis influence tumorigenesis and also have a complex relationship with adiposity. There is evidence to suggest that insulin and the IGF axis play an important role in mediating obesity associated malignancy.

CONCLUSIONS

There is much evidence to support a role for obesity in cancer progression, however further research is warranted to determine the specific effect of excess visceral adipose tissue on tumorigenesis. Investigation of the potential mechanisms underpinning the association, including the role of insulin and the IGF axis, will improve understanding of the obesity and cancer link and may uncover targets for intervention.

Influence of obesity on the risk of esophageal disorders

Obesity is associated with an increased risk of esophageal disorders, including esophageal adenocarcinoma, Barrett esophagus and GERD. For reasons yet unknown, the association between obesity and esophageal adenocarcinoma seems to be stronger than that for other types of obesity-related cancers. Predominantly abdominal or intra-abdominal adiposity (representing visceral fat and other fat within the abdominal cavity), which is more frequently observed in men than in women, is more strongly linked with these esophageal disorders than BMI alone, a finding that might contribute to the striking male predominance of esophageal adenocarcinoma. Research has identified potential mechanisms underlying the strong link between obesity and esophageal conditions. These findings are summarized in this Review, but more research remains to be carried out before these mechanisms are established.

The implication of adiponectin and resistin in gastrointestinal diseases

Adiponectin and resistin, members of the adipokine family, are multi-task hormones involved in several disorders, including those of the alimentary tract. In the present review, eligible studies focusing on the role of adiponectin and resistin in gastrointestinal diseases are manifested together and classified according to anatomic criteria. In addition, similarities and common patterns have been recognized, ultimately revealing an inverse association: the down-regulation of adiponectin and up-regulation of resistin - both in vitro and in vivo - in gastrointestinal disorders, irrespective of their diverse nature - inflammatory, autoimmune or malignant - or anatomic position - esophageal, gastric, of the small intestine, colonic. Finally, a potential role for both adipokines in alimentary tract-related carcinogenesis has been identified, possibly representing a missing link between obesity and cancer.