1. Introduction
Cervical cancer is the fourth most common cancer in the world, accounting for 6.5% of all cancers, after breast, colorectal, and lung cancer. It is also the fourth highest cause of cancer death in women in both high-income and low-middle-income countries, with an estimated mortality rate of 7.7% worldwide (GLOBOCAN 2020) [Reference Sung, Ferlay and Siegel1]. Exposure to high-risk human papillomavirus (HPV) is required but is not a sufficient cause of cervical cancer [Reference Moore, Wark, Hopper, Erbas and Garland2, Reference Xiao, Liu and Wen3]. Oncogenic HPV DNA is present in nearly 100% of invasive cervical cancers. A limited immune response to HPV linked to the host’s genetic make-up may increase the risk of cervical cancer [Reference Howell4]. Many authors have been interested in the research of risk factors related to cervical cancer throughout the last few decades [Reference Machalek, Wark and Tabrizi5]. It appears from their investigations that genetic factors seem to exert a significant influence on the carcinogenesis of the cervix. Notably, the reported results are conflicting. However, mutations in genes involved in cytokine synthesis, such as interleukin 10 (IL-10), appear to be strong predictors of cervical cancer risk [Reference Datta, Tuz Zahora and Abdul Aziz6–Reference Zidi, Gazouani and Stayoussef8]. Physiologically, IL-10 is an essential cytokine for inflammatory modulation. Several cell types are involved in the production of this cytokine, including Th1, Th2, Th17 lymphocytes, B lymphocytes, mast cells, eosinophils, monocytes, macrophages, and dendritic cells [Reference Saraiva, Christensen, Veldhoen, Murphy, Murphy and O’Garra9, Reference Stumhofer, Silver and Laurence10]. The IL-10 gene, which contains five exons, has been found on the long arm of chromosome 1q31-32 in humans [Reference Eskdale, Kube, Tesch and Gallagher11, Reference Trifunović, Miller, Debeljak and Horvat12]. The significance of the IL-10 gene in the control of immune-mediated illness responses has resulted in the discovery of numerous polymorphisms in different portions of the gene, including the promoter region [Reference Howell4, Reference Eskdale, Kube, Tesch and Gallagher11]. The majority of identified genetic polymorphisms are single nucleotide polymorphisms (SNPs). The SNP-592C/A of the IL-10 gene promoter is located near a number of transcription factor binding sites. This SNP has been implicated in the pathogenesis of cutaneous malignant melanoma and prostate, breast, gastric, and cervical cancer [Reference Datta, Tuz Zahora and Abdul Aziz6, Reference Abbas, Mason and Ibad13–Reference Wang, Yang, Xu and Zhong18]. Association studies carried out in different populations have shown that this SNP increases the risk of developing cervical cancer [Reference Datta, Tuz Zahora and Abdul Aziz6, Reference Torres-Poveda, Burguete-García and Bahena-Román17, Reference Singhal, Kumar, Bharadwaj, Hussain and Bharadwaj19]. However, other studies have reported conflicting results [Reference Du, Wang, Richards and Wang7, Reference Bai, Shi, He, Xue and Feng20, Reference Pereira, Trugilo and Okuyama21]. Furthermore, the expression of the IL-10 gene and/or the production of IL-10 has been demonstrated in various types of tumors, suggesting that IL-10 could, by promoting escape from the immune system, constitute a step in tumorigenesis [Reference de Oliveira, Rossi and Nizato22–Reference Niu, Du and Cai24]. Given the contradictory results of numerous studies on the role of SNP-592C/A of the IL-10 gene in the pathogenesis of cervical cancer, we conducted a meta-analysis to assess the association between SNP-592C/A in the IL-10 gene and the risk of cervical cancer.
2. Materials and Methods
2.1. Literature Search Strategy
The identification of initial manuscripts or published articles, available in English, was performed using the online databases PubMed, the Harvard University Library, Web of Science, and Genetics Medical Literature Database. Additional articles were identified from references cited in relevant reports and journals. The key search words “Interleukin-10” or “IL-10,” “−592C/A” or “−592C > A” or “rs1800872,” “polymorphism” or “variant” or “mutation” or “gene” or “cervical tumor” or “cervical cancer” were used to locate and select the articles.
2.2. Inclusion Criteria
The eligibility criteria were as follows: (1) case-control study design evaluating the association of the -592C/A polymorphisms of the IL-10 gene with the risk of cervical cancer, (2) availability of the full scientific manuscript, (3) distribution of polymorphisms in the controls in agreement with Hardy–Weinberg equilibrium (HWE), (4) availability of proportions of the different genotypes (CC, CA, AA for −592C/A of the IL-10 gene) in both cases and controls, and (5) no significant change in the value of the odds ratio (OR).
2.3. Data Extraction
Three authors independently carried out the literature search to optimize the convergence of the retrieved data, including principal author, year of publication, study design, study population, racial and ethnic groups, sample size, genotypic and allelic proportions in cases and controls, HWE calculation, and genetic models tested.
2.4. Statistical Analysis
The statistical analyses were conducted using Review Manager v5.3 and MedCalc v14.8.1. The distribution of the −592C/A polymorphism of the IL-10 gene in agreement with HWE in the controls was evaluated by a chi-square test, with P < 0.05. A pooled OR test with a 95% confidence interval (CI) was used to assess the strength of the association between the −592C/A polymorphism in the IL-10 gene and the risk of cervical cancer, including the recessive model (AA vs. CC + CA), the dominant model (AA + CA vs. CC), and the additive model (A vs. C). To avoid type I error, the level of significance was corrected using Bonferroni’s adjustment during multiple comparisons. An inconsistency (I 2) statistical test was used to determine heterogeneity [Reference Cumpston, Li and Page25, Reference DerSimonian and Laird26]. If there was no heterogeneity (I 2 < 50%), a fixed-effect model (FEM) was retained for interpretation of a global OR. In the case of heterogeneity, the OR was interpreted using a random-effect model (REM). A funnel plot was used to determine bias [Reference Egger, Smith, Schneider and Minder27]. The trial sequential analysis (TSA) software was used to estimate the sample size required for each arm to assess the robustness of the meta-analysis findings with 90% statistical power [Reference Meng, Wang, Zhang, Fan, Zhang and Liang28].
3. Results
3.1. Characteristics of Eligible Studies
Four Caucasian studies with 2221 cases and 1240 controls [Reference Torres-Poveda, Burguete-García and Bahena-Román17, Reference Pereira, Trugilo and Okuyama21, Reference Ivansson, Gustavsson and Magnusson29, Reference Zoodsma, Nolte and Schipper30] and seven Asian studies with 1966 cases and 2071 controls [Reference Datta, Tuz Zahora and Abdul Aziz6, Reference Du, Wang, Richards and Wang7, Reference Bai, Shi, He, Xue and Feng20, Reference Roh, Kim and Seo31–Reference Yu, Ma and Wu34] were eligible to conduct the current meta-analysis out of thirteen studies (Figure 1) (Table 1). Only one study on Africans was found, and it was discarded due to Hardy–Weinberg’s imbalance [Reference Zidi, Gazouani and Stayoussef8]. Another study that had a major impact on the overall OR was also excluded [Reference Singhal, Kumar, Bharadwaj, Hussain and Bharadwaj19].
FIGURE 1: Flow diagram of eligible studies included.
TABLE 1: Genotypic distribution of the IL-10-592C/A polymorphism in eligible studies.
N: number.
3.2. Quantitative Analysis
Table 2 denotes the association between cervical cancer and SNP-592C/A of IL-10 for the genetic models. Overall, a significant association was found between the risk of cervical cancer and the three genetic models, including the recessive (OR (FEM) = 1.30, 95% CI = 1.14–1.49, P=0.0001), dominant (OR (REM) = 1.36, 95% CI = 1.09–1.70, P=0.006), and additive models (OR (REM) = 1.25, 95% CI = 1.09–1.44, P=0.001) (Figure 2).
TABLE 2: Genetic models and SNP-592C/A in the IL-10 gene in cervical cancer.
N: number; P: P value OR; P′: P value of heterogeneity; I 2: inconsistency; recessive model: AA vs. CC + CA; dominant model: AA + CA vs. CC; additive model: A vs. C; ∗ = fixed-effect model, ∗∗ = random-effect model; N = number; α = Bonferroni correction; Sig = Bonferroni significance.
FIGURE 2: Forest plots of the association between the -592C/A polymorphism of the IL-10 gene and cervical cancer for the (a) recessive model, (b) dominant model, and (c) additive model. The pooled OR is represented by a black diamond, the OR in each study is represented by blue squares with square sizes inversely proportionate to the standard error of the OR, and the horizontal lines represent the 95% CI.
Based on analysis by race/ethnicity (Table 2), the -592C/A polymorphism of the IL-10 gene was significantly associated with an increased risk of cervical cancer in Caucasians for the recessive model (OR (FEM) = 1.50, 95% CI = 1.12–2.00, p=0.006), dominant model (OR (REM) = 1.57, 95% CI = 1.03–2.40, P=0.04), and additive model (OR (FEM) = 1.15, 95% CI = 1.15–1.46, P < 0.0001) (Figure 3). Furthermore, an association of this polymorphism with cervical cancer was observed in the Asian populations for the recessive (OR (FEM) = 1.25, 95% CI = 1.07–1.46, P=0.004), dominant (OR (FEM) = 1.26, 95% CI = 1.09–1.46, P=0.002), and additive (OR (FEM) = 1.19, 95% CI = 1.08–1.30, P=0.0002) models (Figure 4). After Bonferroni correction adjusts P value, a nonsignificant association was found between IL-10 -592C/A polymorphism and cancer for the dominant model in Caucasians.
FIGURE 3: Forest plots of the association between SNP-592C/A in the IL-10 gene and cervical cancer for the (a) recessive model, (b) dominant model, and (c) additive model in the Caucasian population. The pooled OR is represented by a black diamond, the OR in each study is represented by blue squares with square sizes inversely proportionate to the standard error of the OR, and the horizontal lines represent the 95% CI.
FIGURE 4: Forest plots of the association between the -592C/A polymorphism of the IL-10 gene and cervical cancer for the (a) recessive model, (b) dominant model, and (c) additive model in the Asian population. The black diamond represents the pooled OR, the blue squares show the OR in each study with square sizes inversely proportional to the standard error of the OR, and the horizontal lines denote the 95% CI.
3.3. Sensitivity Analysis
The stability of the meta-analysis was maintained by removing studies that significantly changed the overall OR and P value after excluding those that deviated from HWE [Reference Zidi, Gazouani and Stayoussef8]. In this regard, only the article by Singhal et al. has been omitted [Reference Singhal, Kumar, Bharadwaj, Hussain and Bharadwaj19].
3.4. Heterogeneity Source
We found heterogeneity for the dominant and additive models with I 2 > 50 and I 2 = 66 percent, respectively, when we excluded studies that deviated from HWE and the ones that significantly affected the cumulative OR value (Figures 2(b) and 2(c)). The genetic models showed no heterogeneity in the race/ethnicity study, except for the dominating pattern in Caucasians (I 2 = 84 percent, P=0.0003) (Figure 3(b)).
3.5. Publication Bias
The evaluation of publication bias was conducted by performing funnel plots. An absence of publication bias was observed for the recessive, dominant, and additive models after removing studies, not in agreement with the HWE and the study modifying the value of the pooled OR (Figure 5).
FIGURE 5: Funnel plots of the (a) recessive model, (b) dominant model, and (c) additive model precision by OR.
4. Results of TSA
The TSA’s outcome is depicted in Figure 6. The conclusions of the present meta-analysis are strong because the required sample size is 3669 and the cumulative z-curve reached the requested sample size by crossing the upper limit of sequential trial monitoring.
FIGURE 6: Trial sequential analysis for IL10-592C/A polymorphism under the genotype contrast model. The x-axis shows the number of participants (cases and controls) of the meta-analysis in each branch. The y-axis z-score shows the z-score. The red line represents the required sample size. The green line represents the conventional test boundary (P=0.05).
5. Discussion
HPV infection is one of the leading causes of cervical cancer, yet it is not sufficient to trigger cervical carcinogenesis. Smoking, HIV, fetal exposure to diethylstilbestrol, and oral contraceptives have all been identified as additional risk factors. Although genetic variables have been linked to carcinogenesis, the mechanism by which the IL-10 gene polymorphism causes cervical cancer is unknown. In vitro, IL-10 has been shown to have powerful immunosuppressive and antiinflammatory activities [Reference de Vries35–Reference Katayama, Hayashi, Nagahira, Konishi, Yamaichi and Oikawa37].
This cytokine is produced by a variety of cell types, such as CD4 T cells and monocytes/macrophages [Reference Gabryšová, Howes, Saraiva and O’Garra38, Reference Rutz and Ouyang39]. Macrophages’ ability to present antigens to T cells, as well as their ability to provide a costimulatory signal to T cells, is reduced by IL-10. It performs this function by inhibiting the activation of class II MHC-11 molecules and specific accessory molecules on their surfaces, including the B7.1 molecule [Reference Costa Brandão Berti, Brajão de Oliveira, Berti and de Oliveira40]. By blocking cell-mediated immune responses and inflammatory reactions, IL-10 can promote carcinogenesis by limiting the development of an adequate antitumor response against tumor cells [Reference Costa Brandão Berti, Brajão de Oliveira, Berti and de Oliveira40, Reference Lin and Karin41].
It is worth noting that, in addition to its inhibitory characteristics, IL-10 stimulates antibody production, as well as the differentiation and proliferation of B lymphocytes, which in turn produce IL-10 [Reference Couper, Blount and Riley42–Reference Sabat, Grütz and Warszawska44]. Furthermore, the expression of the IL-10 gene has been confirmed in various tumors, suggesting that IL-10 could play a nonnegligible role in carcinogenesis by allowing the immune system to escape [Reference Howell4]. In promoter regions, functional polymorphisms of the IL-10 gene such as -592C/A can lead to changes in the affinity of transcriptional factors, thereby altering levels of mRNA expression (dose-dependent effect) of inflammatory cytokines associated with the occurrence of cancer [Reference de Oliveira, Rossi and Nizato22, Reference Fan, Meng, Zhang, Zhang and Liang45].
In the present study, including 4187 cases and 3311 controls, we noted that the −592C/A polymorphism of the IL-10 gene was correlated with the overall risk of cervical cancer for the recessive, dominant, and additive models. This finding is in line with a previous meta-analysis that identified a significant association between the −592C/A polymorphism and an increased risk of cervical cancer in 2396 cases and 1388 controls [Reference Ni, Ye, Teng and Wu46]. Contrary to our results, Guo et al. reported in a meta-analysis of 3,149 cases and 2,237 controls that the −592C/A polymorphism was not globally correlated with cervical cancer for the three genetic models [Reference Guo, Wen and Song14]. A recent meta-analysis with 1,393 cases and 1,307 controls also found conflicting results [Reference Wang, Jiao and Chen47]. In Caucasians and Asians, our meta-analysis adjusted for race and ethnicity found an association between the −592C/A polymorphism and cervical cancer in all models. Some meta-analyses supported our conclusions in some respects. This was the case in the meta-analysis by Guo et al. on the Caucasian population, which found that only the recessive model was associated with an increased risk of cervical cancer [Reference Guo, Wen and Song14], and another meta-analysis from the Asian population, which found that the additive model was associated with the risk of cervical cancer [Reference Ni, Ye, Teng and Wu46]. However, Wang et al. found that the −592C/A polymorphism had no effect on the risk of cervical cancer in Caucasian and Asian populations across all genetic models tested [Reference Wang, Jiao and Chen47].
Furthermore, Torres-Poveda et al. and Pereira et al. found a correlation between the −592C/A polymorphism and cervical cancer in the Mexican and Brazilian populations for all three models, respectively [Reference Torres-Poveda, Burguete-García and Bahena-Román17, Reference Pereira, Trugilo and Okuyama21]. Zoodsma et al., Du et al., and Datta et al. reported that the risk of cervical cancer was correlated with the −592C/A SNP in the IL-10 gene for the dominant and additive models in Netherlander, Chinese, and Bangladeshi populations, respectively [Reference Datta, Tuz Zahora and Abdul Aziz6, Reference Du, Wang, Richards and Wang7, Reference Zoodsma, Nolte and Schipper30]. These discrepancies between studies can be explained by a few factors, including (1) sample size differences between studies, (2) inclusion of studies with allele frequencies that deviate from the HWE, (3) inclusion of studies that change the pooled OR value, (4) population genetic background, and (5) inclusion of studies based on noncancerous cervical lesions [Reference Zidi, Gazouani and Stayoussef8, Reference Singhal, Kumar, Bharadwaj, Hussain and Bharadwaj19, Reference Duvlis, Dabeski, Noveski, Ivkovski and Plaseska-Karanfilska48].
The present study shows certain limitations as follows: the limited number of case and control studies carried out on the association of SNP-592C/A in the IL-10 gene with the risk of cervical cancer, particularly in the Caucasian and African populations (almost absent), and the sample size. Although the sample size requirement showed statistical power of 90%, a more representative sample size from different populations worldwide could confirm or refute a robust conclusion.
6. Conclusions
Based on an analysis of a large sample with precise inclusion criteria, this study reveals that women with the −529C/A polymorphism of the IL-10 gene promoter have a high risk of cervical cancer for genetic models and provides evidence of an association of the IL-10 gene promoter in the pathogenesis of cervical cancer.
7. Disclosure
This manuscript was presented as a preprint in “Association of Interleukin-10 −592C/A Polymorphism and Cervical Cancer Risk: A Meta-Analysis” (Preprint) [Reference Diakite, Kassogue and Maiga49]
Abbreviations
AA vs. CC + CA: Recessive model
AA + CA vs. CC: Dominant model
A vs. C: Additive model
CI: Confidence interval
FE: Fixed effect
Fig: Figure
HWE: Hardy–Weinberg equilibrium
I 2: Inconsistency
IL-10: Interleukin-10
N: Number
OR: Odds ratio
RE: Random effect
vs: Versus.
Data Availability
The supplementary material represents all the data analyzed in this meta-analysis.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Authors’ Contributions
The final manuscript has been read and approved by all authors. Study conceptualization and design were done by BD, YK, MM, and LH. View, collection, analysis, and interpretation of the meta-analysis data were performed by BD, YK, MM, GD, OK, JLH, and LH. BD drafted of the manuscript with assistance from YK, MM, GD, OK, JM, IMB, BT, CBT, BK, AC, SB, SN, RLM, JLH, and LH. Critical review of the manuscript for significant intellectual content was done by YK, MM, GD, OK, JM, IMB, BT, CBT, BK, AC, SN, RLM, JLH, and LH. JLH, LH, and RLM supervised the work.
Acknowledgments
The National Institutes of Health (NIH)/National Cancer Institute (NCI) funded the research mentioned in this article under Award number D43CA260658. The authors thank the National Institutes of Health/NCI (D43CA260658) for their support and the HBNU Consortium, Global Health, FIC (D43 TW010543) for their training support. The authors also thank the Faculty of Medicine and Odontostomatology of the Université des Sciences, Techniques et Technologies de Bamako, University Hospital of Point G, and the team of the Laboratoire de Recherche et de Formation sur les Pathologies Moléculaires (LARFPAM: Laboratory of Research and Training in Molecular Pathology) for logistical support.
Supplementary Materials
PubMed accession numbers and Google scholar link of all data and references are given for meta-analysis.
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