Associations of IL-10 genetic polymorphisms with the risk of urologic cancer: a meta-analysis based on 18,415 subjects

Background Interleukin-10 (IL-10) is a powerful modulator of anti-tumor immune responses. The IL-10 promoter region polymorphisms are known to regulate IL-10 production, and thus are thought to be implicated in tumorigenesis. Recently, the roles of these polymorphisms in urologic cancer have been extensively studied, with conflicting results. Therefore, we conducted the present meta-analysis to better elucidate the correlations between IL-10 polymorphisms and urologic cancer risk. Methods Eligible articles were searched in PubMed, Medline, Embase, Scopus and CNKI up to May 2016. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to detect any potential associations between IL-10 polymorphisms and the risk of urologic cancer. Results A total of 22 case–control studies including 8572 patients and 9843 controls were analyzed. The overall meta-analysis results showed that IL-10 −592C>A polymorphism was significantly associated with urologic cancer in CA versus AA (P = 0.04, OR 0.87, 95% CI 0.76–0.99) and AA versus CC+CA (P = 0.03, OR 1.15, 95% CI 1.02–1.31). Subgroup analyses by cancer types suggested there were significant associations between all the three investigated IL-10 polymorphisms and bladder cancer. However, subgroup analyses by ethnicity only detected a weak association between IL-10 −819C>T and Asian population. Conclusions Our findings suggests that IL-10 −592C>A polymorphism may implicate with urologic cancer risk. Besides, promoter region polymorphisms of IL-10 may serve as potential biological markers, especially for bladder cancer. Furthermore, IL-10 −819C>T polymorphism may contribute to urologic cancer susceptibility in Asians while all the three studied variants of IL-10 did not relate to Caucasian urologic cancer predisposition.


Background
Commonly seen urologic cancers such as prostate cancer, renal cancer, and bladder cancer are leading causes of cancer-related morbidity and mortality globally (Siegel et al. 2014). Despite rapid advances in early diagnosis and surgical treatment over the past few decades, the numbers of new urologic cancer cases and associated deaths are continue to increase, making it becomes one of the major threats to public health worldwide (Ferlay et al. 2015).
To date, the exact cause of urologic cancer remains unclear. Certain environmental factors like smoking habit, heavy alcohol intake, high caloric diet and chemical dyes have been identified as potential etiological factors for urologic cancer. However, the fact that only a small portion of individuals exposed to these carcinogenic agents ultimately develop urologic cancer suggests that genetic susceptibility factors may play a crucial part in its pathogenesis (Jiang et al. 2014).
Interleukin-10 (IL-10), encoded by the IL-10 gene located on chromosome 1q31-32, is a potent regulator Open Access *Correspondence: lishangwei1125@163.com 1 Division of Reproductive Medical Center, West China Second University Hospital, Sichuan University, Chengdu, Sichuan, China Full list of author information is available at the end of the article of anti-tumor immune responses (Eskdale et al. 1997;Mocellin et al. 2005). As a result, certain polymorphisms located in the promoter region of IL-10 gene (−592C>A, −819C>T and −1082A>G), which regulate the expression level of IL-10 protein (Turner et al. 1997;Kingo et al. 2005), were thought to be implicated in the pathogenesis of various kinds of cancers. Recently, many genetic association studies have been carried out to investigate the potential correlations between IL-10 promoter region polymorphisms and urologic cancer risk. However, results of these studies were controversial and the statistical power of individual studies was insufficient. Therefore, we conducted the present meta-analysis to better assess the potential associations of IL-10 genetic polymorphisms with the risk of urologic cancer.

Inclusion criteria
The inclusion criteria for the present study were set prior to the literature search. Eligible studies met all the following conditions: (1) case-control study of unrelated urologic cancer patients and control subjects; (2) evaluation of the associations between IL-10 polymorphisms (−592C>A, −819C>T and −1082A>G) and the risk of urologic cancer; (3) presentation of sufficient data to calculate the odds ratios (ORs) and corresponding 95% confidence intervals (CIs); (4) full text in English or Chinese available. If the report was duplicated or identical patients were enrolled in two studies, only the most recent and complete article was included. Abstracts, family-based association studies, case reports, case series, reviews, editorials, expert opinions and conference presentations were intentionally excluded.

Data extraction and quality assessment
From each included studies, the following data were extracted: references, country of origin, ethnicity of study population, the number of cases and controls, types of urologic cancer, allelic and genotypic frequencies of IL-10 polymorphisms in urologic cancer patients and control subjects, and whether the distributions of IL-10 polymorphisms in the control group were in accordance with Hardy-Weinberg equilibrium (HWE). The Newcastleottawa quality assessment scale (NOS), a classical rating tool which evaluates the credibility of observational studies from three perspectives: selection, comparability and exposure, was used to assess the reliability of all case-control studies included (Zhang et al. 2014). This rating system has a score range of 0-9, and studies with a score of more than 7 were assumed to be of high quality. Two reviewers (Shi and Xie) conducted the data extraction and quality assessment independently. When necessary, the reviewers wrote to the corresponding authors for extra information or raw data. Any discrepancies between two reviewers were resolved by discussion until reaching a consensus. The final results were reviewed by a senior reviewer (Li).

Statistical analysis
All data analyses were performed using Review Manager Version 5.3.3 (The Cochrane Collaboration, Software Update, Oxford, United Kingdom). HWE was explored with the Chi square test. ORs and 95% CIs were employed to evaluate potential associations between IL-10 polymorphisms and the risk of urologic cancer. Heterogeneity between studies was assessed by using the Q test and I 2 statistic. If probability value (P value) of Q test was less than 0.1 or I 2 was greater than 50%, the randomeffect model (REM) would be adopted for analyses due to the existence of significant between-study heterogeneity. Otherwise, the fixed-effect model (FEM) would be applied for analyses. Subgroup analyses were performed based on types of cancer and ethnicity of study population. Sensitivity analyses were carried out by omitting one individual study each time. Publication bias was further evaluated with funnel plots. And a P value of 0.05 or less was considered to be statistically significant for all analyses.

Included studies
The literature search yielded 462 results. After exclusion of irrelevant or duplicate articles by reading titles and abstracts, 39 articles were selected for further evaluation. Among these, a total of 22 case-control studies including 8572 urologic cancer patients and 9843 control subjects met our inclusion criteria (see Fig. 1), 14/22 were about the IL-10 −592C>A polymorphism, 13/22 were about the IL-10 −819C>T polymorphism, and 20/22 were about the IL-10 −1082A>G polymorphism. All included studies were published between 2002 and 2016. Of these, there were 16 studies of prostate cancer, 4 studies of renal cancer, and 2 studies of bladder cancer. All articles were published in English except for two in Chinese. Characteristics of studies analyzing IL-10 −592C>A polymorphism were summarized in Table 1, characteristics of studies examining IL-10 −819C>T polymorphism were summarized in Table 2, and characteristics of studies investigating IL-10 −1082A>G polymorphism were summarized in Table 3.

Risk of bias in included studies
As shown in Tables 1, 2 and 3, the average NOS score of included studies was 7.59 (range from 7 to 8), suggesting that all enrolled articles were of relatively high quality. The improper selection of controls and mismatching baseline characteristics of urologic cancer cases and control subjects (age and/or ethnicity) were the major sources of biases.

IL-10 −592C>A polymorphism and urologic cancer risk
For IL-10 −592C>A polymorphism, a total of 14 studies including 5899 urologic cancer patients and 6181 control subjects were investigated (Dluzniewski et al. 2012;Dwivedi et al. 2015a, b;Eder et al. 2007;Faupel-Badger et al. 2008;Liu et al. 2010;VanCleave et al. 2010;Wang et al. 2009;Winchester et al. 2015;Xu et al. 2005;Zabaleta et al. 2008;Basturk et al. 2005;Cozar et al. 2007;Chang et al. 2016;Chen et al. 2013). HWE test for the control group of each included studies demonstrated that only 1 study deviated from HWE (see Table 1). In order to explore the association between IL-10 −592C>A polymorphism and urologic cancer risk, we compared distribution of genotypes and alleles in every genetic model. For CC versus AA, CA versus AA, CA versus CC+AA, and AA versus CC+CA, between-study heterogeneity was mild, and analyses were performed with FEMs.

IL-10 −819C>T polymorphism and urologic cancer risk
A total of 13 studies with 4655 cancer cases and 6344 healthy controls were enrolled to evaluate the association between IL-10 −819C>T polymorphism and urologic cancer risk (Dwivedi et al. 2015a, b;Faupel-Badger et al. 2008;Liu et al. 2010;VanCleave et al. 2010;Winchester et al. 2015;Zabaleta et al. 2008;Basturk et al. 2005;Cozar et al. 2007;Chang et al. 2016;Chen et al. 2013;Kesarwani et al. 2009;Michaud et al. 2006;Ahirwar et al. 2009). HWE test for the control group of eligible studies revealed that 4 studies violated HWE (see Table 2). All genetic models were tested to detect any differences in genotypic and allelic frequencies of cases and controls. For CT versus TT, there was only trivial between-study heterogeneity, and FEM was employed for analysis. For CC versus CT, CC versus TT, CC versus CT+TT, CT versus CC+TT, TT versus CC+CT, and C versus T, between-study heterogeneity was obvious, and REMs were adopted for analyses. No significant association with urologic cancer was found for IL-10 −819C>T polymorphism in any genetic models (see Figs. 4,5).

Sensitivity analysis
Sensitivity analyses were carried out through removing one individual study each time.

Table 5 Subgroup analyses for IL-10 −819C>T polymorphism and urologic cancer risk
The difference in cases and controls regarding the distributions of investigated genetic polymorphisms in certain genetic model reached the statistically significant level, which is also less than 0.05 are indicated in italics OR odds ratio, CI confidence interval a The number of articles  Table 6 Subgroup analyses for IL-10 −1082A>G polymorphism and urologic cancer risk The difference in cases and controls regarding the distributions of investigated genetic polymorphisms in certain genetic model reached the statistically significant level, which is also less than 0.05 are indicated in italics OR odds ratio, CI confidence interval a The number of articles

Publication bias
Potential publication bias was evaluated with funnel plots. Visual inspection of funnel plots revealed no apparent asymmetry for IL-10 −592C>A, −819C>T, and −1082A>G polymorphisms. And these results indicated that significant publication bias was unlikely.

Discussion
Urologic cancer is a major public health problem. According to a recent survey, prostate cancer, renal cancer and bladder cancer altogether accounted for 13.3% (1879,000/14090,000) new cancer cases and 7.5% (616,000/8201,000) cancer-related deaths worldwide in 2012, making the urologic cancer ranked as the second most common group of malignancies in terms of morbidity, and the third most common group of malignancies in terms of mortality (Ferlay et al. 2015).
To date, the etiologies of urologic cancer are still largely unknown in spite of extensive studies. However, it has become evident recently that multiple immunomodulatory cytokines are implicated in the process of tumor genesis (Kurzrock 2001;Smyth et al. 2004). Among these cytokines, IL-10 is a multifunctional immunological regulator mainly produced by B cells, T cells and activated monocytes/marcophages. As an important modulator of immune responses, IL-10 can be both tumor-promoting and tumor-inhibiting since it has both immunosuppressive and anti-angiogenic functions (Mocellin et al. 2005). On the one hand, the immunosuppressive property of IL-10 may suppress anti-tumor immune responses and promote tumor development. On the other hand, the anti-angiogenic property of IL-10 may inhibit microvasculature formation and tumor growth. Previous studies have found that serum level of IL-10 was significantly elevated in urologic cancer, and it was closely correlated with tumor progression and metastasis (Stearns et al. 1999;Uwatoko et al. 2002;Dwivedi et al. 2015a, b), which suggested that IL-10 may play a vital role in the development of urologic cancer.
Recently, numerous studies have tried to explore the potential associations between IL-10 polymorphisms and the risk of urologic cancer, but the results were contradicted. Thus, we conducted the present metaanalysis to solve the conflict and obtain a more conclusive result. And our overall analyses suggested that IL-10 −592C>A polymorphism was significantly associated with the risk of urologic cancer in CA versus AA, and AA versus CC+CA. However, we failed to detect any significant associations with urologic cancer for IL-10 −819C>T and −1082A>G polymorphisms in overall analyses. Considering the differences of carcinogenic mechanisms for each type of cancer and the importance of ethnic background in genetic investigations, stratified analyses were subsequently performed by categorizing included studies into different subgroups on the basis of types of cancer and ethnicity of study population. When data were stratified by types of cancer, we found that IL-10 −592C>A, −819C>T and −1082A>G polymorphisms were all significantly associated with the risk of bladder cancer in certain genetic models. In addition, the A allele of −592C>A polymorphism and T allele of −819C>T polymorphism conferred an increased susceptibility to bladder cancer. When data were stratified by ethnicity of study population, a significant association with urologic cancer risk in Asians was detected for IL-10 −819C>T polymorphism in CT versus TT. No any other significant associations between IL-10 polymorphisms and urologic cancer risk were observed in subgroup analyses. For the evaluation of the heterogeneity, we found that the between-study heterogeneity remained significant in several subgroup comparisons, suggesting that differences in cancer type and ethnicity could not fully elucidate the observed inconsistent results, and other unmeasured characteristics of study participants may partially attribute to the heterogeneity between studies. Moreover, we noticed a substantial decrease of heterogeneity for IL-10 −592C>A polymorphism when the study performed by Zabaleta et al. (2008) was omitted, and that for IL-10 −819C>T polymorphism when the study conducted by Chen et al. (2013) was removed or that for IL-10 1082A>G polymorphism when the studies of Ianni et al. (2013) and Niu (2011) were excluded, which suggested that these studies were the major sources of the observed heterogeneity.
This study is certainly not without limitations. Firstly, the number of studies investigating the associations of certain IL-10 polymorphisms with renal cancer or bladder cancer is still limited, and sample size of several included studies were obviously not sufficient, which precluded us from drawing definite conclusions. Secondly, our results were based on unadjusted estimates since the majority of included studies failed to report baseline characteristics of individuals, such as age, sex, smoking status and eating habits. And lack of analyses adjusted for these potential confounding factors may affect the reliability of our results. Thirdly, although funnel plots revealed no apparent publication bias, we still could not eliminate the possibility of publication bias since only published studies were included. Fourthly, all included studies were published in English or Chinese, therefore, maybe some qualified articles in other languages were missed. Fifthly, genetic associations of IL-10 polymorphisms with urologic cancer may also be influenced by gene-gene and gene-environmental interactions. It is possible that one certain polymorphism may be associated with the risk of urologic cancer, but due to interactions with multiple genes and environmental factors, the association would no longer be observed.

Conclusions
In conclusion, the current meta-analysis suggests that IL-10 −592C>A polymorphism may implicate with urologic cancer risk. Besides, promoter region polymorphisms of IL-10 may serve as potential biological markers, especially for bladder cancer. Furthermore, IL-10 −819C>T polymorphism may contribute to urologic cancer susceptibility in Asians while all the three studied variants of IL-10 did not relate to Caucasian urologic cancer predisposition. However, it should be pointed out that the present results concerning renal cancer and bladder cancer were based on limited number of case-control studies, and further multi-center studies with larger sample size from different populations are warranted to confirm our results. Besides, given that immunomodulating cytokines play a crucial role in regulating anti-tumor immune responses, future investigations are needed to explore the potential roles of other polymorphisms of these cytokine genes in the occurrence and development of urologic cancer.