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Urinary Prostaglandin E2 Metabolite and Pancreatic Cancer Risk: Case-Control Study in Urban Shanghai

  • Jing Zhao,

    Affiliation Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China

  • Jing Wang,

    Affiliation Department of Epidemiology, Shanghai Cancer Institute, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, China

  • Jinfeng Du,

    Affiliation Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China

  • Hongli Xu,

    Affiliation Department of Epidemiology, Shanghai Cancer Institute, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, China

  • Wei Zhang,

    Affiliation Department of Epidemiology, Shanghai Cancer Institute, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, China

  • Quan-Xing Ni,

    Affiliation Department of Pancreatic and Hepatobiliary Surgery, Fudan University Shanghai Cancer Center, Shanghai, China

  • Herbert Yu,

    Affiliation Epidemiology Program, University of Hawaii Cancer Center, Honolulu, HI, United States of America

  • Harvey A. Risch,

    Affiliation Department of Chronic Disease Epidemiology, Yale School of Public Health and Yale Cancer Center, New Haven, CT, United States of America

  • Yu-Tang Gao ,

    yinggao@sibs.ac.cn (YG); ytgao@vip.sina.com (YTG)

    Affiliation Department of Epidemiology, Shanghai Cancer Institute, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, China

  • Ying Gao

    yinggao@sibs.ac.cn (YG); ytgao@vip.sina.com (YTG)

    Affiliation Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China

Urinary Prostaglandin E2 Metabolite and Pancreatic Cancer Risk: Case-Control Study in Urban Shanghai

  • Jing Zhao, 
  • Jing Wang, 
  • Jinfeng Du, 
  • Hongli Xu, 
  • Wei Zhang, 
  • Quan-Xing Ni, 
  • Herbert Yu, 
  • Harvey A. Risch, 
  • Yu-Tang Gao, 
  • Ying Gao
PLOS
x

Abstract

Pancreatic cancer has been increasing in importance in Shanghai over the last four decades. The etiology of the disease is still unclear. Evidence suggests that the COX-2 pathway, an important component of inflammation, may be involved in the disease. We aimed to evaluate the association between urinary prostaglandin E2 metabolite (PGE-M) level and risk of pancreatic cancer. From a recent population-based case-control study in Shanghai, 200 pancreatic ductal adenocarcinoma cases and 200 gender- and age- frequency matched controls were selected for the present analysis. Urinary PGE-M was measured with a liquid chromatography/mass spectrometric assay. Adjusted unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). A positive association was observed between PGE-M leve and pancreatic cancer risk: OR = 1.63 (95% CI 1.01–2.63) for the third tertile compared to the first. Though the interactions were not statistically significant, the associations tended to be stronger among subjects with diabetes history (OR = 3.32; 95% CI 1.20–9.19) and higher meat intake (OR = 2.12; 95% CI 1.10–4.06). The result suggests that higher urinary PGE-M level may be associated with increased risk of pancreatic ductal adenocarcinoma.

Introduction

Pancreatic cancer is one of the most fatal cancers in the world [1]. In the past 40 years, the incidence of this cancer has been increasing rapidly in China. Among all Chinese cities, Shanghai has the highest mortality from this disease [2]. In 1973, the urban Shanghai pancreatic cancer annual incidence rates were 3.66 per 105 for men and 3.20 per 105 for women [3], whereas in 2000, the rates had substantially increased to 11.22 and 10.93, respectively [3]. The lack of effective techniques for early diagnosis or treatment leads to less than 3% 5-year survival [4]. Cigarette smoking, family history of pancreatic cancer, history of diabetes mellitus and ABO blood group have been linked to the disease, though these factors explain only a fraction of the disease etiology [5,6].

Inflammation has been hypothesized to play a role in carcinogenesis of the pancreas [7]. Epidemiologic studies have suggested that chronic pancreatitis may be involved in some cases of pancreatic cancer [8]. Cyclooxygenase-2 (COX-2), a major enzyme in inflammation, has shown increased protein expression in pancreatic cells during the multistep progression of pancreatic cancer [9] and increased mRNA level in pancreatic cancer compared to adjacent nontumor tissue [10,11]. Nonsteroidal anti-inflammatory drugs (NSAIDs) are inhibitors of COX enzymes and their tumor suppressor effects on pancreatic cancer have been observed in both vitro studies [10,12,13] and some epidemiologic studies [14,15]. During inflammation, COX-2 converts arachidonic acid to PGE2, which may promote tumor development through inhibition of apoptosis, decrease of cell-mediated immunity, or stimulation of angiogenesis [16,17].

Since pancreatic tissue is difficult to access directly, the development of non-invasive technologies, including biomarkers in peripheral blood, pancreatic juice, or urine, could facilitate early detection of the disease [6]. Prostaglandin E2 metabolite (PGE-M) is the urinary metabolite of PGE2 and it can be used as an index of systemic PGE2 production. Several studies have observed that high levels of urinary PGE-M have been associated with increased risk of cancers of the colon and rectum [1820], stomach [21] and breast [22,23], suggesting that urinary PGE-M might be associated with other inflammation-related cancers, including pancreatic cancer. Our study aimed to explore the association between urinary PGE-M levels and pancreatic cancer risk in a case-control study conducted in urban Shanghai.

Materials and Methods

Study population

The current study was conducted within an existing case-control study of pancreatic cancer that has been described previously [24,25]. Briefly, the parent case-control study was performed from December 2006 to January 2011 in urban Shanghai. The subjects recruited were Shanghai residents aged between 35 and 79 years. An “instant case reporting system” was used to identify cases in 37 major hospitals. In total, 1241 patients newly diagnosed with pancreatic cancer were reported to the Shanghai Cancer Institute. Of these patients, 149 (12%) were unable to be contacted or refused to participate, and 184 (14%) were excluded because of diagnoses of benign tumors or non-pancreatic primaries, which left 908 confirmed pancreatic cancer patients in the study. Among them, 311 cases were histologically confirmed as pancreatic ductal adenocarcinoma according to WHO classification of Tumors of the Digestive System. For controls, 1,653 candidates randomly selected from Shanghai Residents Registry were contacted. Among those, 586 (35%) were excluded for other malignant diseases (94), deceasing (30) and refusal (462) and there were 1067 candidates recruited as controls. All participants were interviewed in-person to collect information on cigarette smoking, family history of cancer, personal medical conditions, dietary intakes and various other factors. Body mass index (BMI, weight/height2) was calculated from reported height at age 21 and body weight of a year before interview. Participants were asked to retain overnight urine from 8:00pm to the next 8:00am and the urine was collected before any treatment. The 12-hour urine samples were collected into sterile cups containing 1g ascorbic acid and 5mg EDTA. Samples were kept on ice (4°C) for transportation to the laboratory and processed within 1 hour into long-term storage at −80°C.

For the current analysis, 200 ductal adenocarcinoma cases with pathology diagnoses were randomly selected from the parent case-control study. Two hundred parent-study controls were randomly frequency matched to the 200 cases on gender and age. This study was approved by the institutional human subjects review boards of the Shanghai Cancer Institute and Yale University, and all of the participants provided written informed consent.

PGE-M measurement

Liquid chromatography/mass spectrometric assay (LC/MS/MS) was used to measure levels of urinary 11-α-hydroxy-9,15-dioxo-2,3,4,5-tetranor-prostane-1,20-dioicacid (PGE-M), the major metabolite of PGE2. The method has been described previously [26]. Briefly, 0.5mL urine with 15.0 μL (200ng/mL) of deuterated internal standard (PGE-M-d6) was adjusted to pH 3 with HCl, and PGE-M in the sample was converted to its O-methyloxime derivative with methyloxime HCl. After the urine samples were incubated in a 37°C water bath for 30 min, SepPak plus-C18 was applied to extract the methyloximed PGE-M using ethyl acetate as eluent. The eluate was then evaporated to dryness and residues were redissolved in 80.0μL of reconstituted mobile phase solution. Analysis was performed by liquid chromatography (Phenomenex Kinetex-C18 column) attached to an MDS Sciex API-4000 mass spectrometer with ESI probe. For endogenous PGE-M, the predominant product ion, m/z 336 representing [M-(OCH3+H2O)], and the analogous ion, m/z 339 [M-(OC[2H3]+H2O)] for the deuterated internal standard, were monitored in selected reaction monitoring (SRM) mode. Quantification of endogenous PGE-M used the ratio of the mass chromatogram peak areas of the m/z 336 and 339 ions. Urinary creatinine levels were measured using an Olympus AU5400 clinical chemistry analyzer with 0.1ml urine samples. The 400 samples were tested in five batches. Forty quality-control (QC) specimens (10%) from a single sample were randomly dispersed among the test-sample batches. The laboratory technician was blinded to case/control and QC sample status. The coefficients of variation for PGE-M and creatinine of the QC samples were 4.3% and 3.7%, respectively. The CV for the QC sample PGE-M corrected by creatinine was 4.8%. One sample’s result was below the lower limit of measurement (0.2ng/ml) and was assigned to the lowest PGE-M level group for the analysis.

Statistical Analyses

Student’s t-test for continuous variables and the chi-square test for categorical variables were used to examine differences in basic characteristics between cases and controls. Urinary PGE-M levels were standardized by urinary creatinine values and were expressed as ng/mg creatinine. As the distribution of PGE-M was right-skewed, values were log10 transformed for analysis of continuous trends. Subjects were classified into tertiles according to the PGE-M distribution in controls, with lowest tertile as the reference group. We used two methods to choose the covariates included in the multivariable-adjusted models: (1) the potential confounder is associated with pancreatic cancer risk and with the PGE-M levels and the potential confounder changes the risk estimate by at least 10%; (2) the P value for -2Loglikelihood test is less than 0.05. In the final models, we use two different sets of confounders. Based on the former method, we used the basic model included gender and age as confounders. According to the second method, except for gender and age, attained education, family history of pancreatic cancer, and diabetes history were involved in the full model. To prevent the reverse causality, diabetes history was divided into three categories: no diabetes history, self-reported diabetes diagnosed less than 3 years before interview and diagnosed at least 3 years before interview.

To explore combined effects and modification effects of some a priori risk factors on the association between PGE-M and pancreatic cancer risk, stratified analyses were conducted by gender, history of diabetes mellitus, meat intake, vegetables/fruits intake and current aspirin usage et al. Continuous variables were classified into high vs low levels based on the median levels in controls. Interactions were evaluated with the log likelihood ratio statistic. All analyses were conducted with SAS 9.3 software and all P-values are two-sided.

Results

Basic characteristics of case and control subjects are given in Table 1. Cases and controls were similar in body mass index, smoking exposure, family history of cancer, pancreatitis, vegetables/fruits intake, dietary energy density, regular green tea drinking, and current usage of aspirin. Compared to controls, cases had higher levels of education and greater meat intakes, and were more likely to have family histories of pancreatic cancer, personal histories of diabetes and higher PGE-M levels. Among all the 200 cases, 177 (88.5%) subjects were in stage.

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Table 1. Characteristics of selected pancreatic cancer cases and controls, case-control study in urban Shanghai.

https://doi.org/10.1371/journal.pone.0118004.t001

In the basic model, compared to the lowest tertile, the highest level of urinary PGE-M was associated with increased risk of pancreatic cancer, with odds ratio (OR) estimate of 1.63 (95% CI 1.01–2.63) (Table 2). With regard to the full model, attained education, family history of pancreatic cancer, and diabetes history were not found to alter the magnitudes of association for PGE-M (Table 2).

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Table 2. Association of urinary PGE-M levels and risk of pancreatic cancer.

https://doi.org/10.1371/journal.pone.0118004.t002

We explored the combined effects of PGE-M and several a priori risk factors on pancreatic cancer risk, including gender, diatetes status (yes and no), dietary intake of meat and fruits/vegetables (high and low), and current aspirin usage (yes and no) (Fig. 1, S1 Table). The positive association between PGE-M and pancreatic cancer risk tended to be stronger among participants who had diabetes history and higher meat intake with ORs of 3.32 (95% CI 1.20–9.19) and 2.12 (95% CI 1.10–4.06), respectively (Fig. 1, S1 Table). We also explored potential modifying effects of these factors (S2 Table). The positive association for tertile 3 among all subjects was still significant among participants who reported not using aspirin: OR 1.69 (95% CI 1.02–2.80). Significant interactions of urinary PGE-M were not seen for the five factors (S2 Table). In addition, we explored the associations between urinary PGE-M levels and risk of pancreatic cancer by stages (S3 Table), and the association kept similar for stage II (OR = 1.76, 95% CI = 1.07–2.89).

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Fig 1. Combined effects of PGE-M and some a priori factors on risk for pancreatic cancer.

Adjusted ORs for pancreactic cancer according to the tertiles of PGE-M and diabetes status (A), meat intake (B), vegetables/fruits intake (C), and current aspirin usage (D). Adjusted for gender and age. Diabetes History was considered positive for self-reported diabetes diagnosed at least 3 years before interview.

https://doi.org/10.1371/journal.pone.0118004.g001

Discussion

In the current case-control study, we observed a positive association between high urinary PGE-M level and increased risk of pancreatic cancer. The positive association with high urinary PGE-M level was still significant after exclusion of individuals with current aspirin usage and was stronger among subjects with diabetes history or higher meat intake.

PGE-M is the urinary metabolite of PGE2, and thus indirectly reflects blood levels of PGE2. Excreted urinary metabolites measured by LC/MS/MS provide highly accurate indicators of endogenous eicosanoid production in humans [26,27]. Oral administration of both non-selective and selective inhibitors of COX-2 can result in lower urinary PGE-M levels in healthy individuals, which suggests that urinary PGE-M can reflect COX-2 production and activity [26].

To our knowledge, six epidemiological studies to-date have explored associations between urinary PGE-M levels and cancer risk, including four studies of gastrointestinal neoplasms [1821] and two studies of breast cancer [22,23]. Both a study on advanced/multiple colorectal adenoma [19] and a study on colorectal cancer [18] observed significant associations between PGE-M and disease risk. In a case-series study, urinary PGE-M levels among patients with Crohn’s disease, colorectal cancer and large adenomas were about two fold increased compared to patients who had small polyps or no polyps [20]. For gastric cancer [21], a significantly increasing trend in risk was observed with increasing PGE-M levels among women who had been diagnosed within 46 months after baseline urine collection. For breast cancer, the risk was increased with urinary PGE-M levels among postmenopausal women with no NSAIDs usage [22] or with a BMI<25 kg/m2 [23]. Consistent with these studies, we observed a positive association between high urinary PGE-M level and increased risk of pancreatic cancer. These results suggest that PGE-M, possibly as a marker of inflammation, could be associated with gastrointestinal cancer development.

PGE2 is one of the products of arachidonic acid catalyzed by COX-2, which has been suggested to play a role in the development of certain cancers [16,28]. COX-2 involvement may promote cancer cell proliferation, migration, invasion, and inhibit cell apoptosis via a number of signaling pathways [29]. PGE2 could also regulate angiogenesis and tumor immune-suppression in the tumor microenvironment [16]. Several clinical studies have observed that COX-2 is up-regulated in pancreatic adenocarcinoma [911]. COX-2 mRNA expression was more than 60-fold increased in pancreatic cancer tissue compared to adjacent non-tumor tissue [30]. In the hamster model of chemically induced ductal pancreatic adenocarcinoma, the selective COX-2 inhibitor, Celebrex, was observed to inhibit tumor growth in liver metastases [31]. Various epidemiological studies have suggested that inhibitors of COX-2 could protect against pancreatic cancer [32]. Furthermore, expression loss of 15-hydroxyprostaglandindehydrogenase (15-PGDH), an important enzyme involved in PGE2 degradation, has been linked to tumor formation, including colorectal cancer, lung cancer and transitional bladder cancer [29]. Thus, increased PGE2 may be associated with increased cancer risk, including pancreatic cancer.

Urinary PGE-M is subject to the influence of many factors. Aspirin, a COX-2 inhibitor is related to decreased PGE-M levels [26]. Interestingly, only 9.5% of individuals in our study took aspirin regularly; excluding the individuals with current aspirin usage strengthened the positive association between PGE-M and pancreatic cancer risk. This is adding further evidence supporting the negative relationship between aspirin and PGE-M. Smoking status has been observed to be positively associated with urinary PGE-M level smoking status, which had a dose-response effect [33]. Our data also suggested that urinary PGE-M was higher in ever smokers than never smokers (median (interquartile): 12.71(9.07–19.24) vs 11.51(8.77–16.45) ng/mg Cr). Increased BMI is associated with increased urinary PGE-M level [34]. Consistently, in our study, subjects with BMI more than 28kg/m2 had higher PGE-M level than subjects with BMI less than 24kg/m2 (median (interquartile): 13.55(10.76–18.41) vs 11.42(8.56–16.93) ng/mg Cr).

We also explored combined effects of several a priori factors with PGE-M on pancreatic cancer risk, and found a stronger association among subjects with higher meat intake. Meat contains abundant arachidonic acid [35] (the precusor of PGE2) and increased amount of dietary arachidonic acid probably augmented PGE2 formation [36, 37]. Therefore, meat intake here might be associated with pancreatic cancer through PGE2, which warrants further research. We also observed a significant association between PGE-M and pancreatic cancer among individuals with diabetes, which was reasonable since diabetes was an important risk factor related to pancreatic cancer [38].

Our study has several strengths. The diagnoses of all cases were validated by a panel of five clinical experts who used pathology reports, pathology slides and/or imaging materials, which minimized misclassification of cancer cases. Moreover, only ductal pancreatic adenocarcinoma patients were involved in our study, which increased the homogeneity of the disease studied.

A few potential limitations of the present study should also be considered. Firstly, as a case-control study, our analysis may be subject to reverse causality, where the presence of pancreatic tumors could theoretically increase serum levels of PGE2. However, we did not observe appreciable variation in urinary PGE-M according to disease stage. Secondly, the stratified analyses by stage were limited by power since 88.5% of cases were in stage II. Further study with larger sample size is needed. Thirdly, aspirin or NSAID usage at the time of interview may affect urinary PGE-M levels. However, there were only 18 cases and 20 controls reported current aspirin usage in the current study, and the association was still statistically significant after excluding these individuals.

In summary, the current study suggests that higher levels of urinary PGE-M may be associated with increased pancreatic cancer risk. Large prospective studies would be useful for further exploration.

Supporting Information

S1 Table. Combined effects of PGE-M and some a priori factors on risk for pancreatic cancer.

https://doi.org/10.1371/journal.pone.0118004.s001

(DOCX)

S2 Table. Association of urinary PGE-M levels and risk of pancreatic cancer by potential modifiers.

https://doi.org/10.1371/journal.pone.0118004.s002

(DOCX)

S3 Table. Association of urinary PGE-M levels and risk of pancreatic cancer in different cancer stages.

https://doi.org/10.1371/journal.pone.0118004.s003

(DOCX)

Acknowledgments

We express our sincere appreciation to all of the study participants and research staff involved in the Shanghai Pancreatic Cancer Case-control Study. We thank Lu Sun from the Shanghai Cancer Institute for her help in sample collection. We also thank Hong-Xing Xu and Shaojie Ma for assistance in sample preparation. We are grateful for help from Prof. Huiyong Yin at the Institute for Nutritional Sciences, Chinese Academy of Sciences, for PGE-M measurements consultation.

Author Contributions

Conceived and designed the experiments: YG YTG HR HY. Performed the experiments: JZ JW JD HX WZ QXN. Analyzed the data: JZ JW YG. Contributed reagents/materials/analysis tools: YG. Wrote the paper: JZ YG YTG.

References

  1. 1. Jemal A, Bray F, Center MM, Ferlay J, Ward E, et al. (2011) Global cancer statistics. CA Cancer J Clin 61 (2):69–90. pmid:21296855
  2. 2. Li L (2003) China pancreatic cancer death report. Chin J Epidemiol 24(6):520–2
  3. 3. Gao Y-T, Lu W (2007) Cancer incidence, mortality and survival rates in urban Shanghai (1973–2000). Shanghai: Second Military Medical University Press, pp: 69–124 (in Chinese). pmid:19108398
  4. 4. Gong Z, Holly EA, Bracci PM (2011) Survival in population-based pancreatic cancer patients: San Francisco Bay area, 1995–1999. Am J Epidemiol 174 (12):1373–1381. pmid:22047824
  5. 5. Risch HA, Lu L, Wang J, Zhang W, Ni Q, et al. (2013) ABO blood group and risk of pancreatic cancer: a study in Shanghai and meta-analysis. Am J Epidemiol 177 (12):1326–1337. pmid:23652164
  6. 6. Lowenfels AB, Maisonneuve P (2005) Risk factors for pancreatic cancer. J Cell Biochem 95 (4):649–656. pmid:15849724
  7. 7. McKay CJ, Glen P, McMillan DC (2008) Chronic inflammation and pancreatic cancer. Best Pract Res Cl Ga 22 (1):65–73. .
  8. 8. Duell EJ, Lucenteforte E, Olson SH, Bracci PM, Li D, et al. (2012) Pancreatitis and pancreatic cancer risk: a pooled analysis in the International Pancreatic Cancer Case-Control Consortium (PanC4). Ann Oncol 23 (11):2964–2970. pmid:22767586
  9. 9. Maitra A, Ashfaq R, Gunn CR, Rahman A, Yeo CJ, et al. (2002) Cyclooxygenase 2 expression in pancreatic adenocarcinoma and pancreatic intraepithelial neoplasia: an immunohistochemical analysis with automated cellular imaging. Am J Clin Pathol 118 (2):194–201. pmid:12162677
  10. 10. Molina MA, Sitja-Arnau M, Lemoine MG, Frazier ML, Sinicrope FA (1999) Increased cyclooxygenase-2 expression in human pancreatic carcinomas and cell lines: growth inhibition by nonsteroidal anti-inflammatory drugs. Cancer Res 59 (17):4356–4362 pmid:10485483
  11. 11. Okami J, Yamamoto H, Fujiwara Y, Tsujie M, Kondo M, et al. (1999) Overexpression of cyclooxygenase-2 in carcinoma of the pancreas. Clin Cancer Res 5 (8):2018–2024 pmid:10473081
  12. 12. Funahashi H, Satake M, Dawson D, Huynh NA, Reber HA, et al. (2007) Delayed progression of pancreatic intraepithelial neoplasia in a conditional Kras(G12D) mouse model by a selective cyclooxygenase-2 inhibitor. Cancer Res 67 (15):7068–7071. pmid:17652141
  13. 13. Zhou H, Huang L, Sun Y, Rigas B (2009) Nitric oxide-donating aspirin inhibits the growth of pancreatic cancer cells through redox-dependent signaling. Cancer Lett 273 (2):292–299. pmid:18805632
  14. 14. Anderson KE, Johnson TW, Lazovich D, Folsom AR (2002) Association Between Nonsteroidal Anti-Inflammatory drug use and the incidence of pancreatic cancer. J Natl Cancer I 94 (15):1168–1171. pmid:12165642
  15. 15. Bradley MC, Hughes CM, Cantwell MM, Napolitano G, Murray LJ (2010) Non-steroidal anti-inflammatory drugs and pancreatic cancer risk: a nested case-control study. Br J Cancer 102 (9):1415–1421 pmid:20372155
  16. 16. Wang D, Dubois RN (2010) Eicosanoids and cancer. Nat Rev Cancer 10 (3):181–193. pmid:20168319
  17. 17. Ito H, Duxbury M, Benoit E, Clancy TE, Zinner MJ, et al. (2004) Prostaglandin E2 Enhances pancreatic cancer iInvasiveness through an Ets-1-dependent induction of Matrix Metalloproteinase-2. Cancer Res 64 (20):7439–7446. pmid:15492268
  18. 18. Cai Q, Gao Y-T, Chow W-H, Shu X-O, Yang G, et al. (2006) Prospective study of urinary prostaglandin E2 metabolite and colorectal cancer risk. J Clin Onco 24 (31):5010–5016. pmid:17075120
  19. 19. Shrubsole MJ, Cai Q, Wen W, Milne G, Smalley WE, et al. (2012) Urinary prostaglandin E2 metabolite and risk for colorectal adenoma. Cancer Prev Res 5 (2):336–342. pmid:22166248
  20. 20. Johnson JC, Schmidt CR, Shrubsole MJ, Billheimer DD, Joshi PR, et al. (2006) Urine PGE-M: A metabolite of prostaglandin E2 as a potential biomarker of advanced colorectal neoplasia. Clin Gastroenterol H 4 (11):1358–1365. pmid:16996805
  21. 21. Dong LM, Shu X-O, Gao Y-T, Milne G, Ji B-T, et al. (2009) Urinary prostaglandin E2 metabolite and gastric cancer risk in the Shanghai Women's Health Study. Cancer Epidemiol Biomarkers Prev 18 (11):3075–3078. pmid:19861525
  22. 22. Kim S, Taylor JA, Milne GL, Sandler DP (2013) Association between urinary prostaglandin E2 metabolite and breast cancer risk: a prospective, case–cohort study of postmenopausal women. Cancer Prev Res 6 (6):511–518. pmid:23636050
  23. 23. Cui Y, Shu XO, Gao YT, Cai Q, Ji BT, et al. (2014) Urinary prostaglandin e2 metabolite and breast cancer risk. Cancer Epidemiol Biomarkers Prev 23 (12):2866–2873. pmid:25214156
  24. 24. Wang J, Zhang W, Sun L, Yu H, Ni QX, et al. (2012) Green tea drinking and risk of pancreatic cancer: a large-scale, population-based case-control study in urban Shanghai. Cancer Epidemiol 36 (6):e354–358. pmid:22944495
  25. 25. Risch HA, Lu L, Kidd MS, Wang J, Zhang W, et al. (2014) Helicobacter pylori Seropositivities and Risk of Pancreatic Carcinoma. Cancer Epidemiol Biomarkers Prev 23 (1):172–178. pmid:24234587
  26. 26. Murphey LJ, Williams MK, Sanchez SC, Byrne LM, Csiki I, et al. (2004) Quantification of the major urinary metabolite of PGE2 by a liquid chromatographic/mass spectrometric assay: determination of cyclooxygenase-specific PGE2 synthesis in healthy humans and those with lung cancer. Anal Biochem 334 (2):266–275. pmid:15494133
  27. 27. Wu X, Cai H, Xiang YB, Cai Q, Yang G, et al. (2010) Intra-person variation of urinary biomarkers of oxidative stress and inflammation. Cancer Epidemiol Biomarkers Prev 19 (4):947–952. pmid:20332256
  28. 28. Ding XZ, Hennig R, Adrian TE (2003) Lipoxygenase and cyclooxygenase metabolism: new insights in treatment and chemoprevention of pancreatic cancer. Mol Cancer 2:10 pmid:12575899
  29. 29. Wang D, DuBois RN (2006) Prostaglandins and cancer. Gut 55 (1):115–122. pmid:16118353
  30. 30. Tucker ON, Dannenberg AJ, Yang EK, Zhang F, Teng L, et al. (1999) Cyclooxygenase-2 expression is up-regulated in human pancreatic cancer. Cancer Res 59 (5):987–990 pmid:10070951
  31. 31. Wenger FA, Kilian M, Bisevac M, Khodadayan C, von Seebach M, et al. (2002) Effects of Celebrex and Zyflo on liver metastasis and lipidperoxidation in pancreatic cancer in Syrian hamsters. Clin Exp Metastasis 19 (8):681–687. pmid:12553373
  32. 32. Larsson SC, Giovannucci E, Bergkvist L, Wolk A (2006) Aspirin and nonsteroidal anti-inflammatory drug use and risk of pancreatic cancer: a meta-analysis. Cancer Epidemiol Biomarkers Prev 15 (12):2561–2564. pmid:17164387
  33. 33. Gross ND, Boyle JO, Morrow JD, Williams MK, Moskowitz CS, et al. (2005) Levels of prostaglandin E metabolite, the major urinary metabolite of prostaglandin E2, are increased in smokers. Clin Cancer Res 11 (16):6087–6093. pmid:16115954
  34. 34. Morris PG, Zhou XK, Milne GL, Goldstein D, Hawks LC, et al. (2013) Increased levels of urinary PGE-M, a biomarker of inflammation, occur in association with obesity, aging, and lung metastases in patients with breast cancer. Cancer Prev Res 6 (5):428–436. pmid:23531446
  35. 35. Li D, Ng A, Mann N, Sinclair A (1998) Contribution of meat fat to dietary arachidonic acid. Lipids 33 (4):437–440. pmid:9590632
  36. 36. Adam O (1992) Immediate and long range effects of the uptake of increased amounts of arachidonic acid. Clin Investig 70 (9):721–727. pmid:1450622
  37. 37. Kelley D, Taylor P, Nelson G, Mackey B (1998) Arachidonic acid supplementation enhances synthesis of eicosanoids without suppressing immune functions in young healthy men. Lipids 33 (2):125–130. pmid:9507233
  38. 38. Vincent A, Herman J, Schulick R, Hruban RH, Goggins M (2011) Pancreatic cancer. Lancet 378 (9791):607–620. pmid:21620466