Contributions of NFKB1 ‐94insertion/deletion ATTG polymorphism to the susceptibility of gastrointestinal cancers: A meta‐analysis

Abstract Nuclear factor‐kappa B1 (NF‐κB1), a pleiotropic transcription factor, functions as a critical contributor to tumorigenesis. Growing numbers of case‐control studies were carried out to analyse the potential contribution of NF‐κB1 gene variants to gastrointestinal cancer risk, yet remains conflicting conclusions. Therefore, we conducted this most up‐to‐date meta‐analysis to evaluate the relationship between NF‐κB1 gene insertion (I)/deletion (D) polymorphism, namely −94ins/delATTG or rs28362491, and the susceptibility to gastrointestinal cancers. We searched PubMed, EMBASE and MEDLINE databases updated in April 2021 for relevant studies. Meta‐analysis was carried out by software Stata11.0. The quantification of the relationship was determined by computing the combined odds ratios (ORs) and their corresponding 95% confidence intervals (CIs). Sensitivity analysis, the funnel plot and Begg's rank correlation test were also applied. Our findings indicate that −94ins/delATTG polymorphism could not significantly impact the susceptibility to gastrointestinal cancers. Under any five genetic models, −94ins/delATTG polymorphism was not remarkedly linked to the risk of colorectal, gastric and oesophageal cancer, respectively. The significant role of −94ins/delATTG was only observed in some certain subgroups. Findings here suggest that NF‐κB1 gene −94ins/delATTG polymorphism may not predispose to gastrointestinal cancer susceptibility.

tobacco smoking and over obesity. Apart from the environmental factors, genetic variations are also implicated in the onset and outcome of gastrointestinal cancers. [8][9][10][11] Single nucleotide polymorphisms (SNPs), the most common and effective variant type, are significantly associated with cancer susceptibility. [12][13][14] NF-κB, short for nuclear factor kappa B, is a pluripotent and critical dimer transcription factor. NF-κB orchestrates multiple physiological and pathological processes, particularly in cell survival, differentiation, inflammation and carcinogenesis. [15][16][17][18][19][20][21][22][23] It was originally discovered by Sen and Baltimore in 1986. 24 NF-κB family is consisted of 5 different protein subunits, including NF-κB1 (p50/ p105), NF-κB2 (p52/p100), RelA (p65), c-Rel and RelB, in mammals. 25 NF-κB expression is strictly regulated in normal cells, but it is generally overexpressed in many cancer cells. 26 Upregulation of NF-κB has been observed in several types of cancer, including hepatocellular carcinogenesis, 27,28 colon cancer, 29 breast cancer, 30 ovarian cancer 31 and glioma cancer. 32 Multiple number of NFKB1 gene SNPs were investigated in the implication of cancer. Among them, the rs28362491, namely the −94insertion/deletion ATTG polymorphism, ranks the most intensively investigated SNP. 33,34 The deletion of ATTG bases prevents or reduces the binding to nuclear proteins and results in decreased transcript levels of the NFKB1 gene, thus influencing the stability of mRNA and efficiency of regulating translation. Research regarding NFKB1 gene −94insertion/deletion ATTG polymorphism on its association with gastrointestinal cancer risk was widely performed. However, the conclusions are still contradictory and inconsistent, partly attributed to the underpower and bias of independent studies, especially for small cohorts. Therefore, the exact association between NFKB1 −94insertion/deletion ATTG variant and risk of gastrointestinal cancer awaits to be determined.
Here, a renewed meta-analysis with all potential studies performed before April 2021 was analysed to acquire a clearer impact of NFKB1 −94insertion/deletion ATTG polymorphism on gastrointestinal cancer susceptibility.

| Search strategy
We reported this meta-analysis in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) reporting guidelines.

| Publication selection
We applied an all-sided literature retrieval using EMBASE, PubMed and MEDLINE up to April 2021. We used the following key words to carry out this procedure: (1) NFKB1 or NF-κB1 or nuclear factor kappa B1; (2) −94insertion/deletion ATTG or rs28362491 or SNPs or polymorphisms or polymorphism or variants; and (3) colorectal cancer or gastric cancer or gastrointestinal cancers or oesophageal cancer. To identify all the available studies, we also arranged two authors to screen eligible publications by hand-searching the references of included publications.

| Eligibility criteria
Publications are required to meet the following criteria for inclu-  enough data to calculate odds ratios (ORs) and corresponding 95% confidence intervals (CIs). Editorials, meta-analyses, reviews, research on animals and repetitively published articles were excluded.

| Data extraction
We arranged two researchers (Hanqiang Wu and Jianrong Liang) to acquire the data independently by adopting the unified data table.
The authors acquired the following information from all the studies: surname of the first author, source of control, year of publication, type of cancers, ethnicity of the study subject, numbers of cases and controls, genotyping method, and genotype of SNPs. If the extracted information is disputable, the authors would re-check the references and make sure which extracted information is right. We assessed the methodologic quality of each study using the quality assessment criteria described by previous studies (Table S1). We judged the study quality to be high if the score was more than 9 points or otherwise to be low.

| Statistical methods
We first test if the SNPs in the controls conformed to Hardy-Weinberg equilibrium (HWE) by goodness-of-fit test. The association between NFKB1 rs28362491 and gastrointestinal cancer risk was evaluated by identifying the genotype frequencies of all cases and controls. Odds ratio (OR) and 95% confidence interval (CI) were adopted to assess this rela-

| Literature retrieval results
The screening process of the current meta-analysis was shown in

| Studies characteristics
Among the 16 included studies (Table 1) The SNPs in the control groups of 10 studies complied with HWE, while 6 deviated.

F I G U R E 3
Representative forest plots for the correlation between the NFKB1 −94ins/delATTG polymorphism and respective oesophageal, gastric and colorectal cancers susceptibility. The horizontal lines represent the study-specific ORs and 95% CIs

| Quantitative analysis
The detailed results of the meta-analysis were presented in Table 2 and Figures 2 and 3. The pooled analyses indicated that negative association was detected between the NFKB1 −94ins/delATTG pol-

| Sensitivity analysis
Here, we also carried out a sensitivity analysis by gradually deleting the included studies in a one-by-one manner. The no statistical F I G U R E 4 Sensitivity analysis of the association between NFKB1 −94ins/delATTG polymorphism and gastrointestinal cancer susceptibility. Each point represents the recalculated OR after deleting a separate study F I G U R E 5 Funnel plot analysis of publication bias for NFKB1 −94ins/ delATTG polymorphism. Each point represents a separate study fluctuation of the pooled OR value suggested that the analytic results were reliable and stable (Figure 4).

| Publication bias
Begg's funnel plot did not have significant asymmetry ( Figure 5).
Statistical evidence of Egger's test also could not identify obvious publication bias for all of the polymorphisms.

| Trial sequential analysis
To minimize random errors and strengthen the robustness of our conclusions, we performed TSA ( Figure 6). This analysis showed that the cumulative z-curve did cross the trial sequential monitoring boundary, suggesting that further evidence is needed to verify the conclusions.

| DISCUSS ION
In the current meta-analysis, we comprehensively extract informa-

| CON CLUS ION
In all, our finding has concluded that NFKB1 gene −94ins/delATTG

CO N FLI C T O F I NTE R E S T
The authors declare that there are no competing interests associated with the manuscript.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data sets used and/or analysed during the current study are available from the corresponding author on reasonable request.