Abstract
Objective: The IL-4/IL-4R and IL-6/IL-6R signaling pathways are involved in immune response and play roles in gastric carcinogenesis. To investigate the association between IL-4/IL-4R and IL-6/IL-6R genetic variations and gastric cancer risk, and their prognostic values, we performed a case-control study. The genotypes of the genetic variations were detected using a Mass-array platform. The Helicobacter pylori infection status was determined using a commercial H. pylori immunogold testing kit. We found that the IL-6 rs1800796 G allele was associated with an increased risk of gastric cancer (GG vs. CC: ORadjusted = 2.20, 95% CI = 1.33-3.63; GG/CG vs. CC: ORadjusted = 1.41, 95% CI = 1.09-1.82). The stratified analysis showed that rs1800796 G allele carriers (GG/CG) were associated with an increased risk of gastric cancer in the following subgroups: age >64 years old (ORadjusted = 1.67, 95% CI = 1.17-2.39), female (ORadjusted = 1.82, 95% CI = 1.09-3.05), positive for H. pylori infection (ORadjusted = 1.54, 95% CI = 1.07-2.22), non-cardiac gastric cancer (ORadjusted = 1.53, 95% CI = 1.15-2.04), stage T3-T4 tumor (ORadjusted = 1.41, 95% CI = 1.06-1.88), and gastric cancer with median to high differentiation (ORadjusted = 1.45, 95% CI = 1.08-1.96). None of the genetic variations were associated with overall survival. In short, we concluded that the IL-6 rs1800796 GG genotype is a risk factor for gastric cancer and that rs1800796 G allele carriers have an increased risk of gastric cancer; this association was stronger in individuals that were >64 years old, female, or positive for H. pylori infection. None of the genetic variations were associated with gastric cancer prognosis.
Keywords: IL-4, IL-4R, IL-6, IL-6R, genetic variation, gastric cancer, associations
Introduction
Gastric cancer is the fifth-most common type of cancer and the second-most prevalent cause of cancer-related deaths worldwide [1]. More than one-half of gastric cancer cases worldwide are diagnosed in eastern Asia, predominantly in China [2]. Gastric cancer is a complex and progressive disease; complex genetic and environmental interactions contribute to its initiation and progression [3]. Environmental factors, including Helicobacter pylori infection, excessive salt or alcohol intake, smoking, and genetic variations [4] are all risk factors for the development of gastric cancer.
In 1994, the World Health Organization and the International Agency for Research on Cancer identified H. pylori as a class I carcinogen. The infection rate of H. pylori is approximately 40-50% of the global human population, and studies have shown that people with H. pylori infection are five times more likely to develop gastric cancer than people without H. pylori infection [5,6]. H. pylori colonization can cause chronic inflammation, which significantly increases the risk of developing duodenal and gastric ulcers and gastric cancer. Epidemiologic studies have suggested that the interaction between the host genetic background and H. pylori contributes to the development of gastric cancer. IL1B, a proinflammatory factor that mediates the inflammatory response and strongly inhibits gastric acid secretion [7], is upregulated in response to H. pylori infection. In addition, we have shown that genetic variations in IL-1B associate with the risk of gastric cancer [8,9]. The host immune response that is triggered by H. pylori could be balanced by an anti-inflammatory response mediated by T helper 2 (Th2) cytokines, such as IL-10 and IL-4. We have shown that a shift in the Th1/Th2 balance can predict the progression of gastric disease caused by H. pylori [10]. Although it has been hypothesized that genetic variations in IL-4/IL-4R associate with gastric cancer risk, the results of epidemiologic studies have been inconclusive and have shown differences among different ethnic backgrounds [11-13]. IL-6 acts as both a pro- and anti-inflammatory cytokine [14] and regulates the immune response. It has also been shown that IL-6 may facilitate carcinogenesis through several mechanisms [15]. Epidemiologic studies have investigated the association of IL-6/IL-6R genetic variants with the risk [13,16-20] and prognosis [21] of gastric cancer, but the conclusions have been inconsistent [20,22-24]. Thus, we performed a case-control study to assess the association of IL-4/IL-4R and IL-6/IL-6R genetic variations with the risk and prognosis (determined by the number of overall survival (OS) days of gastric cancer.
Materials and methods
Study subjects
This case-control study enrolled 479 gastric cancer patients and 483 age- and sex-matched healthy controls. All patients were histologically diagnosed to have gastric cancer, and the controls were individuals who came to the hospital for routine physical examinations. Data on the demographic features of the healthy controls were collected via a questionnaire, and data on the clinical features of the cancer patients were collected from their medical records. The clinical stages of the cancers were classified according to the American Joint Commission for Cancer Staging Manual, 6th edition. The survival status of patients were obtained by on-site interviews, direct calling, or reviews of medical charts. The Institutional Review Board of the Nanjing First Hospital approved this protocol, and written informed consent was obtained from all of the participants.
DNA extraction and genotyping
First, we selected the IL-4/IL-4R and IL-6/IL6R genetic variations to evaluate by reviewing the literature on IL-4/IL-4R and IL-6/IL6R genetic variants and their associations with gastric cancer risk. For the genetic variations that we selected, we retrieved related information from the National Center for Biotechnology Information dbSNP database (http://www.ncbi.nlm.nih.gov/projects/SNP). Then, we selected the genetic variations based on the following the criteria: (1) the minor allele frequency (MAF) was not <5% in the Han Chinese population; (2) the variation was positioned in an exon, promoter region, 5’untranslated region (UTR), or 3’UTR; and (3) the variation has been associated with cancer risk. Finally, we chose six IL-4/IL-4R genetic variations and four IL-6/IL-6R genetic variations to study further (Table S1).
DNA extraction and genotyping were performed as previously described [25]. In brief, DNA was extracted using the GoldMag-Mini Whole Blood Genomic DNA Purification Kit according to the manufacture’s protocol (GoldMag Co. Ltd. Xi’an, China). DNA purity was evaluated by spectrophotometry (DU530UV/VIS spectrophotometer, Beckman Instruments, Fullerton, CA, USA), and genotyping was performed with Sequenom MassARRAY RS1000 according to the standard protocol. We used MassARRAY Assay Design version 3.1.2.2 (Sequenom Inc., San Diego, CA) to design PCR and extension primers for the genetic variations. After PCR, the amplified DNA products were cleaned using EXO-SAP (Sequenom), extended by IPLEX chemistry, desalted using Clean Resin (Sequenom), and spotted onto Spectrochip matrix chips using a nanodispenser (Samsung). The chips were run in duplicate on a Sequenom MassArray MALDI-TOF MassArray system. To confirm the genotyping results, we randomly selected 15% of the samples for re-genotyping, and the results showed a concordance rate of 100%.
H. pylori serum assays
To determine whether the study participants had H. pylori infections, a commercial H. pylori immunogold testing kit (Kangmei Tianhong Biotech Co., Ltd, Beijing, China) was used to test for H. pylori antibodies; this test had a sensitivity of 98.29% and a specificity of 98.51% for the detection of H. pylori infection in the Chinese population.
Statistical analysis
The differences in the demographic features of the two groups were assessed by the t test or the chi-square (χ2) test. Hardy-Weinberg equilibrium (HWE) in the control group was tested using a goodness of fit χ2 test. The odds ratios (ORs) and 95% confidence intervals (CIs) for the association of the genetic variations with the risk of gastric cancer were calculated using a logistic regression based on SAS software (Version 9.1; SAS Institute, Cary, NC, USA). A sub-group analysis based on clinical and pathological characteristics was conducted to check if there was a significant association between the genetic variation and gastric cancer risk. Survival curves were assessed by Kaplan-Meier analyses. The association between the survival time and the genetic variation was estimated using the log-rank test. Hazard ratios (HRs), which were used to determine the prognostic values of the genetic variations for patient survival, were calculated using univariate Cox regression models or multivariate Cox regression models if the genetic variation was significantly associated with gastric cancer risk. The data was calculated using SPSS 11.0 software (SPSS, Chicago, IL, USA). A two-sided p-value <0.05 was considered statistically significant.
Results
Characteristics of the study population
The demographic and exposure data of all the participants are summarized in Table S2. There were no differences between the two groups with respect to age and gender (age: P = 0.748, gender: P = 0.881). The frequencies of H. pylori infection, cigarette smoking, and alcohol consumption were higher in the study patients than in the controls (H. pylori: P = 0.039, cigarette smoking: P<0.001, alcohol consumption: P<0.001). The observed frequencies of all of the tested genotypes in the controls did not deviate from HWE (Table S1). The distributions of the genetic variations in the case patients and the controls are presented in Table 1.
Table 1.
Associations between IL-4 and IL-6 polymorphisms and gastric cancer risk
| Genotype | Cases, n (%) | Controls, n (%) | OR (95% CI) | AOR (95% CI)a | p-value |
|---|---|---|---|---|---|
| IL-4 rs2243248 | |||||
| TT | 421 (87.89) | 420 (86.96) | Reference | Reference | |
| GT | 57 (11.90) | 62 (12.84) | 0.92 (0.63, 1.35) | 0.92 (0.63, 1.37) | 0.693 |
| GG | 1 (0.21) | 1 (0.21) | 1.00 (0.06, 16.04) | 0.74 (0.05, 12.11) | 0.836 |
| GT/GG | 58 (12.11) | 63 (13.04) | 0.92 (0.63, 1.35) | 0.92 (0.63, 1.35) | 0.671 |
| Additive model | 0.92 (0.64, 1.34) | 0.92 (0.63, 1.34) | 0.660 | ||
| IL-4 rs2070874 | |||||
| TT | 309 (64.51) | 321 (66.46) | Reference | Reference | |
| TC | 147 (30.69) | 142 (29.40) | 1.08 (0.81, 1.42) | 1.03 (0.78, 1.37) | 0.817 |
| CC | 23 (4.80) | 20 (4.14) | 1.19 (0.64, 2.22) | 1.24 (0.66, 2.32) | 0.511 |
| TC/CC | 170 (35.49) | 162 (33.54) | 1.09 (0.84, 1.42) | 1.06 (0.81, 1.39) | 0.685 |
| Additive model | 1.08 (0.87, 1.35) | 1.07 (0.85, 1.34) | 0.576 | ||
| IL-4R rs2057768 | |||||
| TT | 125 (26.10) | 139 (28.78) | Reference | Reference | |
| CT | 241 (50.31) | 239 (49.48) | 1.12 (0.83, 1.51) | 1.16 (0.86, 1.58) | 0.331 |
| CC | 113 (23.59) | 105 (21.74) | 1.20 (0.84, 1.71) | 1.17 (0.81, 1.69) | 0.405 |
| CT/CC | 354 (73.90) | 344 (71.22) | 1.14 (0.86, 1.52) | 1.17 (0.87, 1.56) | 0.298 |
| Additive model | 1.10 (0.92, 1.31) | 1.09 (0.91, 1.31) | 0.349 | ||
| IL-4R rs2107356 | |||||
| CC | 192 (40.08) | 202 (41.82) | Reference | Reference | |
| TC | 224 (46.76) | 215 (44.51) | 1.10 (0.84, 1.44) | 1.15 (0.87, 1.51) | 0.340 |
| TT | 63 (13.15) | 66 (13.66) | 1.00 (0.68, 1.50) | 0.98 (0.65, 1.46) | 0.908 |
| TC/TT | 287 (59.92) | 281 (58.18) | 1.08 (0.83, 1.39) | 1.09 (0.84, 1.42) | 0.500 |
| Additive model | 1.03 (0.85, 1.24) | 1.02 (0.85, 1.23) | 0.813 | ||
| IL-4R rs1805015 | |||||
| TT | 402 (83.92) | 404 (83.64) | Reference | Reference | |
| CT | 76 (15.87) | 76 (15.73) | 1.01 (0.71, 1.42) | 1.00 (0.70, 1.42) | 0.994 |
| CC | 1 (0.21) | 3 (0.62) | 0.34 (0.04, 3.24) | 0.34 (0.04, 3.29) | 0.351 |
| CT/CC | 77 (16.08) | 79 (16.36) | 0.98 (0.70, 1.38) | 0.97 (0.69, 1.38) | 0.880 |
| Additive model | 0.96 (0.69, 1.33) | 0.95 (0.68, 1.33) | 0.754 | ||
| IL-4R rs1801275 | |||||
| AA | 326 (68.06) | 329 (68.12) | Reference | Reference | |
| GA | 137 (28.60) | 133 (27.54) | 1.04 (0.78, 1.38) | 1.04 (0.78, 1.38) | 0.812 |
| GG | 16 (3.34) | 21 (4.35) | 0.77 (0.39, 1.50) | 0.71 (0.36, 1.41) | 0.331 |
| GA/GG | 153 (31.94) | 154 (31.88) | 1.00 (0.77, 1.32) | 0.99 (0.75, 1.30) | 0.934 |
| Additive model | 0.97 (0.77, 1.22) | 0.95 (0.75, 1.20) | 0.662 | ||
| IL-6 rs6949149 | |||||
| TT | 151 (31.52) | 144 (29.81) | Reference | Reference | |
| GT | 228 (47.60) | 248 (51.35) | 0.88 (0.66, 1.17) | 0.89 (0.66, 1.19) | 0.421 |
| GG | 100 (20.88) | 91 (18.84) | 1.05 (0.73, 1.51) | 1.06 (0.73, 1.54) | 0.758 |
| GT/GG | 328 (68.48) | 339 (70.19) | 0.92 (0.70, 1.21) | 0.93 (0.70, 1.23) | 0.610 |
| Additive model | 1.01 (0.84, 1.21) | 1.02 (0.85, 1.22) | 0.863 | ||
| IL-6 rs10499563 | |||||
| TT | 298 (62.21) | 303 (62.73) | Reference | Reference | |
| TC | 163 (34.03) | 157 (32.51) | 1.06 (0.81, 1.39) | 1.08 (0.82, 1.42) | 0.602 |
| CC | 18 (3.76) | 23 (4.76) | 0.80 (0.42, 1.51) | 0.84 (0.44, 1.60) | 0.601 |
| TC/CC | 181 (37.79) | 180 (37.27) | 1.02 (0.79, 1.33) | 1.05 (0.80, 1.36) | 0.747 |
| Additive model | 0.99 (0.79, 1.23) | 1.01 (0.81, 1.26) | 0.948 | ||
| IL-6 rs1800796 | |||||
| CC | 226 (47.18) | 268 (55.49) | Reference | Reference | |
| CG | 203 (42.38) | 187 (38.72) | 1.29 (0.99, 1.68) | 1.28 (0.98, 1.68) | 0.071 |
| GG | 50 (10.44) | 28 (5.80) | 2.12 (1.29, 3.48) | 2.20 (1.33, 3.63) | 0.002 |
| GC/GG | 253 (52.82) | 215 (44.51) | 1.40 (1.08, 1.80) | 1.41 (1.09, 1.82) | 0.009 |
| Additive model | 1.38 (1.13, 1.68) | 1.39 (1.14, 1.71) | 0.001 | ||
| IL-6R rs2228145 | |||||
| AA | 163 (34.03) | 157 (32.51) | Reference | Reference | |
| CA | 232 (48.43) | 235 (48.65) | 0.95 (0.72, 1.26) | 0.96 (0.72, 1.29) | 0.803 |
| CC | 84 (17.54) | 91 (18.84) | 0.89 (0.62, 1.29) | 0.88 (0.61, 1.29) | 0.519 |
| CA/CC | 316 (65.97) | 326 (67.49) | 0.93 (0.71, 1.22) | 0.94 (0.72, 1.24) | 0.678 |
| Additive model | 0.94 (0.79, 1.13) | 0.94 (0.79, 1.13) | 0.541 |
Adjusted for age, gender, smoking, drinking, and H. pylori infection status.
p-values <0.05 are shown in bold. AOR, adjusted odds ratio; OR, odds ratio.
Associations between genetic variations and gastric cancer risk
There was a significant difference in the distribution of the rs1800796 genotype between the cancer group and the control group. Logistic regression revealed that the rs1800796 GG and GG/CG genotypes were associated with increased gastric cancer risk (GG vs. CC: adjusted OR = 2.20, 95% CI = 1.33-3.63, P = 0.002; GG/CG vs. CC: adjusted OR = 0.009, 95% CI = 1.09-1.82, P = 0.009; additive model: adjusted OR = 1.39, 95% CI: 1.14-1.71, P = 0.001). No significant association was observed between the other genetic variations and gastric cancer risk (Table 1). To investigate the contribution of potential interactions between IL-4/IL-4R and IL-6/IL-6R to gastric cancer risk, we recalculated the combined genotypes of IL-4/IL-4R and IL-6/IL-6R genetic variations but did not find any significant associations (Tables S3 and S4).
Stratification analysis
To further assess the association between rs1800796 and the risk of gastric cancer, we performed a stratified analysis by age, gender, H. pylori infection status, tumor stage, and tumor site using a co-dominant model (CG/GG vs. CC). The increased risk of 1800796 G allele carriers (GG/CG) for gastric cancer remained significant in the following subgroups: age >64 years old (adjusted OR = 1.67, 95% CI = 1.17-2.39, P = 0.005), female (adjusted OR = 1.82, 95% CI = 1.09-3.05, P = 0.023), positive for H. pylori infection (adjusted OR = 1.54, 95% CI = 1.07-2.22, P = 0.023), non-gastric cardiac adenocarcinoma (NGCA; adjusted OR = 1.53, 95% CI = 1.15-2.04, P = 0.003), tumor stage T3-T4 (adjusted OR = 1.41, 95% CI = 1.06-1.88, P = 0.020), and median to high differentiation (adjusted OR = 1.45, 95% CI = 1.08-1.96, P = 0.015; Table 2).
Table 2.
Stratification analysis of the associations between rs1800796 genotypes and gastric cancer risk
| Variables | Rs1800796 (cases/controls) | AOR (95% CI) | p-valuea | |
|---|---|---|---|---|
|
| ||||
| CC | CG/GG | |||
| Age | ||||
| ≤64 | 115/125 | 96/87 | 1.16 (0.80, 1.70) | 0.432 |
| >64 | 111/143 | 107/100 | 1.67 (1.17, 2.39) | 0.005 |
| Gender | ||||
| Male | 163/187 | 190/171 | 1.30 (0.96, 1.75) | 0.091 |
| Female | 63/81 | 63/44 | 1.82 (1.09, 3.05) | 0.023 |
| H. pylori infection | ||||
| Positive | 121/133 | 140/98 | 1.54 (1.07, 2.22) | 0.019 |
| Negative | 105/135 | 113/117 | 1.28 (0.88, 1.85) | 0.193 |
| Differentiation | ||||
| Low | 93/268 | 99/215 | 1.34 (0.95, 1.89) | 0.091 |
| Median to high | 133/268 | 154/215 | 1.45 (1.08, 1.96) | 0.015 |
| Clinical stage | ||||
| I-II | 76/268 | 83/215 | 1.39 (0.95, 2.01) | 0.088 |
| III-IV | 150/268 | 170/215 | 1.41 (1.06, 1.88) | 0.020 |
| Tumor site | ||||
| Cardia | 72/268 | 66/215 | 1.15 (0.78, 1.68) | 0.493 |
| Non-cardia | 154/268 | 187/215 | 1.53 (1.15, 2.04) | 0.003 |
Adjusted for age, gender, smoking, drinking, and H. pylori infection status.
AOR, adjusted odds ratio.
Associations between genetic variations and clinical outcomes
Follow-ups were conducted with 460 gastric cancer patients to obtain survival information. To assess associations between genetic variations and prognosis, we used univariate Cox regression analysis to calculate HRs for patients with heterozygous and homozygous genotypes and to compare them with HRs for patients with the wild type genotype. We did not find any associations between the genetic variations and OS (Table 3), indicating that these genetic variations have no predictive value for gastric cancer.
Table 3.
Analysis of associations between genetic variations and clinical outcomes
| Genotype | Cases, n | Death, n (%) | Log-rank p-value | HR |
|---|---|---|---|---|
| IL-4 rs2248 | ||||
| TT | 406 | 255 (0.63) | Reference | |
| GT/GG | 54 | 31 (0.57) | 0.734 | 1.07 (0.74, 1.55) |
| IL-4 rs2070874 | ||||
| TT | 301 | 192 (0.64) | Reference | |
| TC/CC | 159 | 94 (0.59) | 0.417 | 1.11 (0.87, 1.42) |
| IL-4R rs2057768 | ||||
| TT | 119 | 72 (0.61) | Reference | |
| CT/CC | 341 | 214 (0.63) | 0.451 | 1.05 (0.92, 1.20) |
| IL-4R rs2107356 | ||||
| CC | 182 | 108 (0.59) | Reference | |
| TC/TT | 278 | 178 (0.64) | 0.317 | 1.13 (0.89, 1.44) |
| IL-4R rs1805015 | ||||
| TT | 388 | 241 (0.62) | Reference | |
| CT/CC | 72 | 45 (0.63) | 0.745 | 1.03 (0.88, 1.20) |
| IL-4R rs1801275 | ||||
| AA | 316 | 197 (0.62) | Reference | |
| GA/GG | 144 | 89 (0.62) | 0.843 | 1.03 (0.80, 1.32) |
| IL-6 rs6949149 | ||||
| TT | 144 | 88 (0.61) | Reference | |
| GT/GG | 316 | 198 (0.63) | 0.510 | 1.04 (0.92, 1.18) |
| IL-6 rs10499563 | ||||
| TT | 286 | 183 (0.64) | Reference | |
| TC/CC | 174 | 103 (0.59) | 0.417 | 1.11 (0.87, 1.41) |
| IL-6 rs1800796 | ||||
| CC | 220 | 137 (0.62) | Reference | |
| GC/GG | 240 | 149 (0.62) | 0.952 | 1.00 (0.89, 1.13) |
| IL-6R rs2228145 | ||||
| AA | 156 | 96 (0.62) | Reference | |
| CA/CC | 304 | 190 (0.63) | 0.873 | 1.02 (0.80, 1.30) |
HR was estimated using the univariate Cox regression model.
Discussion
A total of 479 gastric cancer patients and 483 age- and gender-matched healthy controls in a Chinese population were recruited for this population-based case-control study. The results revealed that IL-6 rs1800796 was associated with an increased risk of gastric cancer and that this association was maintained in the following subgroups: older age (>64 years), female, positive for H. pylori infection, NGCA, gastric cancer with median to high differentiation, and stage T3-T4 gastric cancer. In addition, prognostic analysis of 460 patients with survival times up to 5 years showed that none of the selected genetic variations were associated with survival of gastric cancer patients.
IL-6 is located at chromosome 7q21.3 and contains five exons and four introns. Previously, four genetic variations (-174G/C, rs1800795; -572 or -634G/C, rs1800796; -597A/G, rs1800797; and -6331T/C, rs10499563) in the promoter region were associated with a risk of gastric cancer [16,17,26]. However, two studies of these variations in the Chinese population have shown conflicting conclusions [14,15]; this inconsistency is possibly due to the different populations (northern or southern Chinese populations) evaluated or due to the different sample sizes of their studies (215 vs. 375 patients). To attempt to resolve this inconsistency, we evaluated the associations between genetic variations and gastric cancer risk in a mid-east Chinese Han population. We showed that IL-6 rs1800796 was associated with gastric cancer risk, and this is consistent with the results of a meta-analysis that also show that the rs1800796GG genotype is associated with an increased risk of cancer [13,19,20,27]; specifically, a significant association was observed in the pooled results of the Asian population [13,28] and with the results of a study on genetic variations and cancer risk in a Korean population [29]. These studies also did not show a significant association between IL-6 s1800796GG and the risk of gastric cancer [18,23,27,30,31], possibly because of the occurrence of different frequencies of the rs1800796G allele in different races. The frequency of the rs1800796G allele is known to be 23.9% in an Asian population and 93.8% in a European population [27]. In this study, we found that the frequency of the rs1800796G allele was 25.15% in a Chinese population. Moreover, the latest meta-analysis concluded that rs1800796 is associated with cancer risk in Asians, but not in Caucasians [32]. However, for gastric cancer, one study with limited samples reported a negative result in Caucasians [33]. Thus, such an association is unclear in Caucasians and should be investigated further. It has also been shown that the IL-6 rs1800796 genetic variation is associated with the level of IL-6 in serum [34]. Because the rs1800796 genetic variation is in the promoter region of IL-6, it could affect the rate of transcription; the C allele genetic variant is associated with increased transcription of IL-6 when compared with the G allele [35,36]. In addition, individuals carrying the GG genotype are found to have higher IL-6 levels [37,38]. Further, circulating blood levels of IL-6 have been shown to function as potential diagnostic biomarkers for gastric cancer [39,40].
In the stratification analysis, we observed that the carriers of the rs1800796G allele (GG/CG) in the older age (>64 years), female, and ‘positive for H. pylori infection’ subgroups had an increased risk of gastric cancer. It is well known that older individuals have longer exposures to risk factors, which enhances the risk of gastric cancer. The association between the genetic variations and gastric cancer risk observed in the female subgroup may be due to differences in the lifestyles of females and males; for example, females may smoke and drink less than males. For the individuals that were positive for H. pylori infection, rs1800796 was associated with an increased risk of gastric cancer, and this is consistent with the fact that H. pylori infection is a risk factor for gastric cancer. The subgroup analysis also revealed that the rs1800796 allele was associated with NGCA, stage T3-T4 cancer, and cancer with median to high differentiation, thus indicating that the association between the rs1800796 allele and the risk of gastric cancer could be affected by the pathological characteristics of gastric cancer.
We observed no significant association between the genetic variations and the prognosis of gastric cancer. Although serum IL-6 levels have been associated with survival of gastric cancer patients [41] and IL-6 genetic variations (rs1800796, rs8192284) have been shown to affect the prognosis and OS of patients with gastric cancer [21], we did not observe a significant association between rs1800796 and OS in our study. This may be due to differences in sample sizes (the previously published study involved 161 gastric cancer patients) and the different MAFs of rs1800796 in Asian and European populations.
Although similar findings have been previously reported, a novelty of this study is that we analyzed genetic variations involved in the IL-4/IL-4R and IL-6/IL-6R pathways in gastric cancer. In addition, we conducted a subgroup analysis based on clinical characteristics (age, gender, and H. pylori infection status) and pathological characteristics (differentiation, clinical stage, and tumor site). More importantly, we evaluated the prognostic value of these genetic variations using data from 460 Chinese patients who were followed up for up to five years. Nevertheless, some limitations of this study should be noted. First, the relatively small sample size may have limited the statistical power, especially in the multiple stratified analysis. Further, studies with a larger sample size are required to confirm our findings. Second, several environmental factors, such as diet and history of gastric disease, were not included in this study and may influence gastric cancer risk. Such an influence could be minimized by more restrictive case selection criteria. Third, the associations between some of the genetic variations and gastric cancer risk have been identified previously, which may weaken the novelty of this study. However, even though such associations in our Chinese population are unclear, the results of this study will inform future research in this area. Finally, the genetic variations included in this study were selected based on their potential functional roles in cancer occurrence, but their functions remain unclear. Therefore, the functions of the genetic variations require further elucidation.
In conclusion, this case-control study demonstrated that the IL-6 rs1800796 allele IL-6 associates with gastric cancer risk, and the association is stronger in individuals that are >64 years old, female, or positive for H. pylori infection. None of the genetic variations that we analyzed are associated with the prognosis of gastric cancer.
Acknowledgements
This study was supported by grants from the Jiangsu 333 High-level Talents Cultivating Project to B. H (no. BRA201702), the Jiangsu Provincial Medical Youth Talent to B.H (QNRC2016066) and Y.P (QNRC2016074), the Innovation Team of Jiangsu Provincial Health-strengthening Engineering by Science and Education (CXTDB2017008).
Disclosure of conflict of interest
None.
Supporting Information
References
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