Insulin secretion as a determinant of pancreatic cancer risk

Pancreatic endocrine and exocrine signaling and crosstalk in physiological and pathological status

The pancreas, an organ with dual functions, regulates blood glucose levels through the endocrine system by secreting hormones such as insulin and glucagon. It also aids digestion through the exocrine system by secreting digestive enzymes. Complex interactions and signaling mechanisms between the endocrine and exocrine functions of the pancreas play a crucial role in maintaining metabolic homeostasis and overall health. Compelling evidence indicates direct and indirect crosstalk between the endocrine and exocrine parts, influencing the development of diseases affecting both. From a developmental perspective, the exocrine and endocrine parts share the same origin-the "tip-trunk" domain. In certain circumstances, pancreatic exocrine cells may transdifferentiate into endocrine-like cells, such as insulin-secreting cells. Additionally, several pancreatic diseases, including pancreatic cancer, pancreatitis, and diabetes, exhibit potential relevance to both endocrine and exocrine functions. Endocrine cells may communicate with exocrine cells directly through cytokines or indirectly by regulating the immune microenvironment. This crosstalk affects the onset and progression of these diseases. This review summarizes the history and milestones of findings related to the exocrine and endocrine pancreas, their embryonic development, phenotypic transformations, signaling roles in health and disease, the endocrine-exocrine crosstalk from the perspective of diseases, and potential therapeutic targets. Elucidating the regulatory mechanisms of pancreatic endocrine and exocrine signaling and provide novel insights for the understanding and treatment of diseases.

Hyperinsulinemia in Obesity, Inflammation, and Cancer

The relative insufficiency of insulin secretion and/or insulin action causes diabetes. However, obesity and type 2 diabetes mellitus can be associated with an absolute increase in circulating insulin, a state known as hyperinsulinemia. Studies are beginning to elucidate the cause-effect relationships between hyperinsulinemia and numerous consequences of metabolic dysfunctions. Here, we review recent evidence demonstrating that hyperinsulinemia may play a role in inflammation, aging and development of cancers. In this review, we will focus on the consequences and mechanisms of excess insulin production and action, placing recent findings that have challenged dogma in the context of the existing body of literature. Where relevant, we elaborate on the role of specific signal transduction components in the actions of insulin and consequences of chronic hyperinsulinemia. By discussing the involvement of hyperinsulinemia in various metabolic and other chronic diseases, we may identify more effective therapeutics or lifestyle interventions for preventing or treating obesity, diabetes and cancer. We also seek to identify pertinent questions that are ripe for future investigation.

DPP4i, thiazolidinediones, or insulin and risks of cancer in patients with type 2 diabetes mellitus on metformin-sulfonylurea dual therapy with inadequate control

INTRODUCTION

This study aims to compare the risks of cancer among patients with type 2 diabetes mellitus (T2DM) on metformin-sulfonylurea dual therapy intensified with dipeptidyl peptidase 4 inhibitors (DPP4i), thiazolidinediones, or insulin.

RESEARCH DESIGN AND METHODS

We assembled a retrospective cohort data of 20 577 patients who were free of cancer and on metformin-sulfonylurea dual therapy, and whose drug treatments were intensified with DPP4i (n=9957), insulin (n=7760), or thiazolidinediones (n=2860) from January 2006 to December 2017. Propensity-score weighting was used to balance out baseline covariates across the three groups. HRs for any types of cancer, cancer mortality, and all-cause mortality were assessed using Cox proportional-hazards models.

RESULTS

Over a mean follow-up period of 34 months with 58 539 person-years, cumulative incidences of cancer, cancer mortality, and all-cause mortality were 0.028, 0.009, and 0.072, respectively. Patients intensified with insulin had the highest incidence of all-cause mortality (incidence rate=3.22/100 person-years) and the insulin itself posed the greatest risk (HR 2.46, 95% CI 2.25 to 2.70, p<0.001; 2.44, 95% CI 2.23 to 2.67) compared with thiazolidinediones and DPP4i, respectively. Comparing between thiazolidinediones and DPP4i, thiazolidinediones was associated with higher risk of cancer (HR 1.43, 95% CI 1.25 to 1.63) but not cancer mortality (HR 1.21, 95% CI 0.92 to 1.58) and all-cause mortality (HR 0.99, 95% CI 0.88 to 1.11). Insulin was associated with the greatest risk of cancer mortality (HR 1.36, 95% CI 1.09 to 1.71; 1.65, 95% CI 1.31 to 2.07) compared with thiazolidinediones and DPP4i, respectively.

CONCLUSIONS

For patients with T2DM on metformin-sulfonylurea dual therapy, the addition of DPP4i was the third-line medication least likely to be associated with cancer mortality and cancer effect among three options, and posed no increased risk for all-cause mortality when compared with thiazolidinediones.

Environmental risk factors for pancreatic cancer: an update

Pancreatic cancer (PC) is one of the most aggressive diseases. Only 10 % of all PC cases are thought to be due to genetic factors. Here, we analyzed the most recently published case-control association studies, meta-analyses, and cohort studies with the aim to summarize the main environmental factors that could have a role in PC. Among the most dangerous agents involved in the initiation phase, there are the inhalation of cigarette smoke, and the exposure to mutagenic nitrosamines, organ-chlorinated compounds, heavy metals, and ionizing radiations. Moreover, pancreatitis, high doses of alcohol drinking, the body microbial infections, obesity, diabetes, gallstones and/or cholecystectomy, and the accumulation of asbestos fibers seem to play a crucial role in the progression of the disease. However, some of these agents act both as initiators and promoters in pancreatic acinar cells. Protective agents include dietary flavonoids, marine omega-3, vitamin D, fruit, vegetables, and the habit of regular physical activity. The identification of the factors involved in PC initiation and progression could be of help in establishing novel therapeutic approaches by targeting the molecular signaling pathways responsive to these stimuli. Moreover, the identification of these factors could facilitate the development of strategies for an early diagnosis or measures of risk reduction for high-risk people.

The role of insulin and IGF system in pancreatic cancer

The importance of the IGF system in carcinogenesis has been established for many solid cancers. It is well known that individuals with higher circulating levels of the IGF1 ligand present an increased risk of cancer. However, therapies with monoclonal antibodies targeting the IGF1 receptor (IGF1R) have been largely unsuccessful. One of the potential reasons for this failure is the existence of the highly homologous insulin receptor (IR), which appears to be at least equally efficient as the IGF1R in the transition of mitogenic signals to the nucleus and promotion of cell growth. Furthermore, IGF1 and insulin receptors can form hybrid receptors sensitive to stimulation of all three ligands of the system: insulin, IGF1, and IGF2. Although the connection between insulin, diabetes, and cancer has been established for years now, clear evidence that demonstrate the redundancy of insulin and insulin receptors and insulin-like growth factors and their receptors in cancer is missing. In this review, we focus on the contribution of insulin and IGFs to carcinogenesis in the insulin-producing organ, the pancreas. We give a short summary on the complexity of insulin and the IGF system in the pancreas and their potential roles in pancreatic cancer, especially pancreatic ductal adenocarcinoma. Finally, we discuss drug-targeting options of this system and the rationale of simultaneous targeting of both the insulin and the IGF systems.

Nutrients from fruit and vegetable consumption reduce the risk of pancreatic cancer

PURPOSE

Pancreatic cancer is a devastating disease for which the role of dietary factors remains inconclusive. Our objective was to evaluate the risk of pancreatic cancer associated with nutrients found in fruits and vegetables and nutrient supplementation using a clinic-based case-control design.

METHODS

Our study included 384 rapidly ascertained cases and 983 controls frequency-matched on age at time of recruitment (in 5-year increments), race, sex, and region of residence. All subjects provided demographic information and completed a 144-item food frequency questionnaire in which they reported no change to their diet within 5 years prior to entering the study. Logistic regression was used to calculate odds ratios and 95 % confidence intervals, adjusted for age, sex, smoking, body mass index, energy intake, and alcohol consumption.

RESULTS

Results show a significant (trend p value < 0.05) inverse association between pancreatic cancer and nutrient/supplement groupings in a dose-dependent manner including magnesium, potassium, selenium, alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein and zeaxanthin, niacin, total alpha-tocopherol, total vitamin A activity, vitamin B6, and vitamin C. Adjusting for diabetes or total sugar intake did not result in significant changes.

CONCLUSION

We conclude that most nutrients obtained through consumption of fruits and vegetables may reduce the risk of developing pancreatic cancer.

The complexities of obesity and diabetes with the development and progression of pancreatic cancer

Pancreatic cancer (PC) is one of the most lethal malignant diseases with the worst prognosis. It is ranked as the fourth leading cause of cancer-related deaths in the United States. Many risk factors have been associated with PC. Interestingly, large numbers of epidemiological studies suggest that obesity and diabetes, especially type-2 diabetes, are positively associated with increased risk of PC. Similarly, these chronic diseases (obesity, diabetes, and cancer) are also a major public health concern. In the U.S. population, 50 percent are overweight, 30 percent are medically obese, and 10 percent have diabetes mellitus (DM). Therefore, obesity and DM have been considered as potential risk factors for cancers; however, the focus of this article is restricted to PC. Although the mechanisms responsible for the development of these chronic diseases leading to the development of PC are not fully understood, the biological importance of the activation of insulin, insulin like growth factor-1 (IGF-1) and its receptor (IGF-1R) signaling pathways in insulin resistance mechanism and subsequent induction of compensatory hyperinsulinemia has been proposed. Therefore, targeting insulin/IGF-1 signaling with anti-diabetic drugs for lowering blood insulin levels and reversal of insulin resistance could be useful strategy for the prevention and/or treatment of PC. A large number of studies have demonstrated that the administration of anti-diabetic drugs such as metformin and thiazolidinediones (TZD) class of PPAR-γ agonists decreases the risk of cancers, suggesting that these agents might be useful anti-tumor agents for the treatment of PC. In this review article, we will discuss the potential roles of metformin and TZD anti-diabetic drugs as anti-tumor agents in the context of PC and will further discuss the complexities and the possible roles of microRNAs (miRNAs) in the pathogenesis of obesity, diabetes, and PC.

An overview of genetic polymorphisms and pancreatic cancer risk in molecular epidemiologic studies

Background

Although pancreatic cancer has been extensively studied, few risk factors have been identified, and no validated biomarkers or screening tools exist for early detection in asymptomatic individuals. We present a broad overview of molecular epidemiologic studies that have addressed the relationship between pancreatic cancer risk and genetic polymorphisms in several candidate genes and suggest avenues for future research.

Methods

A comprehensive literature search was performed using the PubMed database.

Results

Overall, individual polymorphisms did not seem to confer great susceptibility to pancreatic cancer; however, interactions of polymorphisms in carcinogen-metabolizing genes, DNA repair genes, and folate-metabolizing genes with smoking, diet, and obesity were shown in some studies. The major problem with these studies is that, due to small sample sizes, they lack sufficient statistical power to explore gene–gene or gene–environment interactions. Another important challenge is that the measurement of environmental influence needs to be improved to better define gene–environment interaction. It is noteworthy that 2 recent genome-wide association studies of pancreatic cancer have reported that variants in ABO blood type and in 3 other chromosomal regions are associated with risk for this cancer, thus providing new insight into pancreatic cancer etiology.

Conclusions

As is the case in other complex diseases, common, low-risk variants in different genes may act collectively to confer susceptibility to pancreatic cancer in individuals with repeated environmental exposures, such as smoking and red meat intake. Clarification of gene–gene and gene–environmental interaction is therefore indispensable for future studies. To address these issues, a rigorously designed molecular epidemiologic study with a large sample is desirable.

Glycemic index, glycemic load, and the risk of pancreatic cancer among postmenopausal women in the women's health initiative observational study and clinical trial

BACKGROUND

Several reports have suggested that conditions associated with hyperinsulinemia and insulin resistance, such as diets high in carbohydrates, may influence the risk of pancreatic cancer, although results from prior studies have been mixed.

METHODS

We utilized data from the population-based women's health initiative (WHI) cohort to determine whether dietary factors that are associated with increased postprandial blood glucose levels are also associated with an increased risk of pancreatic cancer. The WHI included 161,809 postmenopausal women of ages 50-79, in which 332 cases of pancreatic cancer were identified over a median of 8 years of follow-up; 287 of these cases met the criteria for analysis. A validated 122-item food frequency questionnaire was used to estimate dietary glycemic load (GL), glycemic index (GI), total and available carbohydrates, fructose and sucrose. Baseline questionnaires and physical exams provided information on demographic, medical, lifestyle, and anthropometric characteristics. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between the exposures of interest and pancreatic cancer risk, with adjustment for potential confounders.

RESULTS

Dietary GL, GI, carbohydrates, fructose, and sucrose were not associated with increased risk of pancreatic cancer. The multivariable adjusted HR for the highest vs. the lowest quartile of GL was 0.80 (95% CI = 0.55-1.15, trend p = 0.31) and 1.13 (95% CI = 0.78-1.63, trend p = 0.94) for GI. The results remained negative when individuals with a history of diabetes were excluded.

CONCLUSIONS

Our results do not support the hypothesis that dietary intake of carbohydrates is associated with increased risk of pancreatic cancer.

Anthropometric measures, body mass index, and pancreatic cancer: a pooled analysis from the Pancreatic Cancer Cohort Consortium (PanScan)

BACKGROUND

Obesity has been proposed as a risk factor for pancreatic cancer.

METHODS

Pooled data were analyzed from the National Cancer Institute Pancreatic Cancer Cohort Consortium (PanScan) to study the association between prediagnostic anthropometric measures and risk of pancreatic cancer. PanScan applied a nested case-control study design and included 2170 cases and 2209 control subjects. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression for cohort-specific quartiles of body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]), weight, height, waist circumference, and waist to hip ratio as well as conventional BMI categories (underweight, <18.5; normal weight, 18.5-24.9; overweight, 25.0-29.9; obese, 30.0-34.9; and severely obese, > or = 35.0). Models were adjusted for potential confounders.

RESULTS

In all of the participants, a positive association between increasing BMI and risk of pancreatic cancer was observed (adjusted OR for the highest vs lowest BMI quartile, 1.33; 95% CI, 1.12-1.58; P(trend) < .001). In men, the adjusted OR for pancreatic cancer for the highest vs lowest quartile of BMI was 1.33 (95% CI, 1.04-1.69; P(trend) < .03), and in women it was 1.34 (95% CI, 1.05-1.70; P(trend) = .01). Increased waist to hip ratio was associated with increased risk of pancreatic cancer in women (adjusted OR for the highest vs lowest quartile, 1.87; 95% CI, 1.31-2.69; P(trend) = .003) but less so in men.

CONCLUSIONS

These findings provide strong support for a positive association between BMI and pancreatic cancer risk. In addition, centralized fat distribution may increase pancreatic cancer risk, especially in women.

Cardiorespiratory fitness and digestive cancer mortality: findings from the aerobics center longitudinal study

Although higher levels of physical activity are inversely associated with risk of colon cancer, few prospective studies have evaluated overall digestive system cancer mortality in relation to cardiorespiratory fitness (CRF). The authors examined this association among 38,801 men ages 20 to 88 years who performed a maximal treadmill exercise test at baseline in the Aerobics Center Longitudinal Study (Dallas, TX) during 1974 to 2003. Mortality was assessed over 29 years of follow-up (1974-2003). Two hundred eighty-three digestive system cancer deaths occurred during a mean 17 years of observation. Age-adjusted mortality rates per 10,000 person-years according to low, moderate, and high CRF groups were 6.8, 4.0, and 3.3 for digestive system cancer (P(trend) < 0.001). After adjustment for age, examination year, body mass index, smoking, drinking, family history of cancer, personal history of diabetes, hazard ratios (95% confidence intervals) for overall digestive cancer deaths for those in the middle and upper 40% of the distribution of CRF relative to those in the lowest 20% were 0.66 (0.49-0.88) and 0.56 (0.40-0.80), respectively. Being fit (the upper 80% of CRF) was associated with a lower risk of mortality from colon [0.61 (0.37-1.00)], colorectal [0.58 (0.37-0.92)], and liver cancer [0.28 (0.11-0.72)] compared with being unfit (the lowest 20% of CRF). These findings support a protective role of CRF against total digestive tract, colorectal, and liver cancer deaths in men.

A prospective study of physical activity and the risk of pancreatic cancer among women (United States)

Background

Several epidemiologic studies have examined the association between physical activity and pancreatic cancer risk; however, the results of these studies are not consistent.

Methods

This study examined the associations of total, moderate, and vigorous physical activity to pancreatic cancer in a cohort of 33,530 U.S. women enrolled in the Breast Cancer Detection Demonstration Project (BCDDP). At baseline (1987–1989), information on physical activity over the past year was obtained using a self-administered questionnaire. Cox proportional hazards regression was used to estimate relative risks (RR) and 95% confidence intervals of pancreatic cancer risk.

Results

70 incident cases of pancreatic cancer were ascertained during 284,639 person years of follow-up between 1987–1989 and 1995–1998. After adjustment for age, body mass index, smoking status, history of diabetes, and height, increased physical activity was related to a suggestively decreased risk of pancreatic cancer. The RRs for increasing quartiles of total physical activity were 1.0, 0.80, 0.66, 0.52 (95% CI = 0.26, 1.05; p_trend = 0.05). This association was consistent across subgroups defined by body mass index and smoking status. We also observed statistically non-significant reductions in pancreatic cancer risk for women in the highest quartile of moderate (RR = 0.57; 95% CI = 0.26, 1.26) and highest quartile of vigorous physical activity (RR = 0.63; 95% CI = 0.31, 1.28) compared to their least active counterparts.

Conclusion

Our study provides evidence for a role of physical activity in protecting against pancreatic cancer.

Dietary glycemic load, added sugars, and carbohydrates as risk factors for pancreatic cancer: the Multiethnic Cohort Study

BACKGROUND

Because elevated blood glucose concentrations have been shown to be associated with greater risk of pancreatic cancer, a high dietary glycemic load, which is based on an empirical measure of blood glucose response after food consumption, has been hypothesized as a pancreatic cancer risk factor. However, results so far are scarce and inconsistent.

OBJECTIVE

We analyzed data for 162 150 participants in the Hawaii-Los Angeles Multiethnic Cohort Study to investigate associations between glycemic load, dietary carbohydrates, sucrose, fructose, total sugars, and added sugars and the risk of pancreatic cancer.

DESIGN

Dietary intake was assessed at baseline by using a quantitative food-frequency questionnaire. During 8 y of follow-up, 434 incident pancreatic cancer cases occurred.

RESULTS

Glycemic load and added sugars were not significantly associated with pancreatic cancer risk. The risk increased with higher intakes of total sugars, fructose, and sucrose, and the association with fructose was significant when the highest and lowest quartiles were compared (relative risk: 1.35; 95% CI: 1.02, 1.80; P for trend = 0.046). A significant association was found with fruit and juices intake (1.37; 1.02, 1.84; P for trend = 0.04) but not with soda intake. Statistical evidence of a significant interaction with body mass index was present only for sucrose intake (P = 0.04). A comparison of the highest and lowest quartiles of sucrose intake in overweight or obese participants gave a relative risk of 1.46 (0.95-2.25; P for trend = 0.04), but the comparison was not significant in normal-weight participants.

CONCLUSIONS

High fructose and sucrose intakes may play a role in pancreatic cancer etiology. Conditions such as overweight or obesity in which a degree of insulin resistance may be present may also be important.

Body mass index, physical activity and the risk of pancreatic cancer in relation to smoking status and history of diabetes: a large-scale population-based cohort study in Japan--the JPHC study

OBJECTIVE

The effects of BMI and physical activity on the risk of pancreatic cancer were investigated in a large population-based cohort study in Japan (JPHC study). In particular, we explored how these effects were influenced by smoking status and a history of diabetes.

METHODS

In total, 99,670 participants (47,499 men, and 52,171 women) were followed for an average of 11 years through the end of 2003. Hazard ratios (HR) and their 95% confidence intervals (CI) were estimated by Cox proportional hazards models.

RESULTS

A total of 224 incident cases (128 men, 96 women) of pancreatic cancer were identified. A statistically significant excess risk of pancreatic cancer was associated with current smoking (HR=1.8, CI 1.1-3.0) and a history of diabetes (HR=2.1, CI 1.3-3.5) among men. A similar increase in risk associated with current smoking (HR=2.0, CI 0.9-4.4) and diabetes (HR=1.5, CI 0.7-3.5) was also seen among women. BMI was inversely associated with risk of pancreatic cancer among men, especially among current male smokers or diabetes patients, but no association was found among women. Leisure-time physical activity was not associated with risk in either men or women.

CONCLUSIONS

Our study confirms the association between cigarette smoking, history of diabetes and increased risk of pancreatic cancer. However, our data suggest that the association between BMI and risk of pancreatic cancer in this Japanese population may be different from that in Western populations.

Body mass index and physical activity as risk factors for pancreatic cancer: the Multiethnic Cohort Study

OBJECTIVE

To examine body mass index (BMI) and physical activity as risk factors for pancreatic cancer.

METHODS

Eight-year prospective data from 77,255 men and 90,175 women including 237 and 235 pancreatic cancer cases, respectively, in the Hawaii-Los Angeles Multiethnic Cohort Study were analyzed. Participants completed a questionnaire that included questions on body weight, height, and physical activity. Cox proportional hazards models were calculated to estimate relative risks (RR) of pancreatic cancer by levels of BMI and total physical activity (as metabolic equivalents (METs)) adjusted for several potential confounders.

RESULTS

Obesity (BMI > or = 30 kg/m(2)) was associated with an increased pancreatic cancer risk in men (RR = 1.51 (95% CI: 1.02-2.26)), but a reduced risk in women (RR = 0.65 (95% CI: 0.43-0.99)). In men the risk was higher in never smokers than in current or former smokers, though differences were not statistically significant. Physical activity was not associated with pancreatic cancer risk in either men or women.

CONCLUSION

The findings suggest, that a BMI of > or = 30 kg/m(2) may be a risk factor for pancreatic cancer in men. No evidence of an effect of physical activity on risk was found.

Obesity, recreational physical activity, and risk of pancreatic cancer in a large U.S. Cohort

BACKGROUND

Obesity and physical activity, in part through their effects on insulin sensitivity, may be modifiable risk factors for pancreatic cancer.

METHODS

The authors analyzed data from the American Cancer Society Cancer Prevention Study II Nutrition Cohort to examine the association between measures of adiposity, recreational physical activity, and pancreatic cancer risk. Information on current weight and weight at age 18, location of weight gain, and recreational physical activity were obtained at baseline in 1992 via a self-administered questionnaire for 145,627 men and women who were cancer-free at enrollment. During the 7 years of follow-up, 242 incident pancreatic cancer cases were identified among these participants. Cox proportional hazards modeling was used to compute hazard rate ratios (RR) and to adjust for potential confounding factors including personal history of diabetes and smoking.

RESULTS

We observed an increased risk of pancreatic cancer among obese [body mass index (BMI) >/= 30] men and women compared with men and women of normal BMI [<25; RR, 2.08; 95% confidence interval (95% CI), 1.48-2.93, P(trend) = 0.0001]. After adjustment for between BMI, risk of pancreatic cancer was independently increased among men and women who reported a tendency for central weight gain compared with men and women reporting a tendency for peripheral weight gain (RR, 1.45; 95% CI, 1.02-2.07). We observed no difference in pancreatic cancer incidence rates between men and women who were most active (>31.5 metabolic equivalent hours per week) at baseline compared with men and women who reported no recreational physical activity (RR, 1.20; 95% CI, 0.63-2.27).

CONCLUSION

This study, along with several recent studies, supports the hypothesis that obesity and central adiposity are associated with pancreatic cancer risk.

Alcohol and pancreatic cancer

Findings obtained from numerous prospective cohort and case-control studies on alcohol consumption and pancreatic cancer risk have been inconsistent, with many confounding variables present in various investigations. However, heavy alcohol consumption has been known to be a major cause of chronic pancreatitis and a risk factor for type 2 diabetes mellitus, both of which are linked to pancreatic cancer. It has been established that an extensive normal interaction exists between the exocrine and endocrine pancreas, as well as in inflammatory processes and carcinogenesis. Alcohol and its metabolites (acetaldehyde and fatty acid ethyl esters) can alter metabolic pathways involved in the inflammatory response and carcinogenesis, and they are mediated by one or more of the following mechanisms: (1) premature activation of zymogens; (2) induction of the inflammatory response through activation of nuclear transcription factors, including nuclear factor-kappa and activation protein 1; (3) increased production of reactive oxygen species, resulting in oxidative DNA damage and altered effect of dietary antioxidants; (4) activation of pancreatic stellate cells, which leads to fibrosis; (5) gene mutation in enzymes related to cytochrome P450, glutathione S-transferase, aldehyde dehydrogenase, cationic trypsinogen, and pancreatic secretory trypsin inhibitor; (6) synergistic effects of ethanol and tobacco carcinogen on NNK [nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone] metabolism; and (7) dysregulation of proliferation and apoptosis. These various metabolic effects of alcohol can lead to or interact with other risk factors (genetic, dietary, environmental, and lifestyle factors) that result in acute and chronic pancreatitis and diabetes mellitus and, ultimately, affect the multistep process of carcinogenesis toward the development of pancreatic cancer.

Etiology of pancreatic cancer, with a hypothesis concerning the role of N-nitroso compounds and excess gastric acidity

In the United States, pancreatic cancer is the fourth most frequent cause of cancer death in males as well as females, after lung, prostate or breast, and colorectal cancer. Each year, approximately 30 000 Americans are diagnosed with pancreatic cancer and about the same number die of it. Germline mutations in a few genes including p16 and BRCA2 have been implicated in a small fraction of cases, as has chronic pancreatitis. The one established risk factor for pancreatic cancer is cigarette smoking: current smokers have two to three times the risk of nonsmokers. Studies of dietary factors have not been entirely consistent but do suggest associations of higher risk with consumption of smoked or processed meats or with animal foods in general and lower risk with consumption of fruits and vegetables. Colonization by Helicobacter pylori appears to increase risk, and a history of diabetes mellitus may also increase risk. The purpose of this epidemiologic review is to consider the possibility that risk of pancreatic cancer is increased by factors associated with pancreatic N-nitrosamine or N-nitrosamide exposures and with chronic excess gastric or duodenal acidity. Host genetic variation in inflammatory cytokine mechanisms may also be involved in this process. Many features of the evidence bearing on the pathophysiology of pancreatic cancer appear to support connections with N-nitroso compounds and with gastric acidity.