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Year : 2015  |  Volume : 52  |  Issue : 6  |  Page : 112--115

A meta-analysis of the association between Chlamydia pneumoniae infection and lung cancer risk

X Hua-Feng, W Yue-Ming, L Hong, D Junyi 
 Department of Emergency, The 6th Affiliated Hospital of Wenzhou Medical University, Lishui People's Hospital 323000, Zhejiang, Lishui, China

Correspondence Address:
D Junyi
Department of Emergency, The 6th Affiliated Hospital of Wenzhou Medical University, Lishui People's Hospital 323000, Zhejiang, Lishui, China
China

Abstract

Objective: The association between Chlamydia pneumoniae infection and lung cancer risk was not clear with small number of cases in each study. The aim of this meta-analysis was to evaluate the correlation between pneumonia infection and lung cancer risk by pooling the open published papers. Materials and Methods: We searched the electronic databases of Medline, EMBASE, Web of Science, and China National Knowledge Infrastructure databases for publications related to the association between pneumonia infection and lung cancer risk. Odds ratio (OR) and its 95% confidence interval (95% CI) was used to assess the correlation. The data were pooled by Stata11.0 software (Stata Corporation, College Station, TX, USA). Results: Thirteen publications, involving 2549 lung cancer patients and 2764 controls were included in this meta-analysis. The pooled results indicated that the C. pneumoniae infection significant increased the risk of lung cancer OR = 2.07 (95% CI: 1.43–2.99) by random effect model. And for serum IgG, 12 publications reported the IgG positive rate in lung cancer patients and relative healthy controls. The pooled OR was 2.22 (95% CI: 1.41–3.50) by using the random effects model which indicated that the IgG positive rate was significantly higher in lung cancer patients than that of healthy controls. The sensitivity analysis indicated the pooled OR was not sensitive to a single study. However, Begger's funnel plot and Egger's line regression analysis indicated significant publications bias for this meta-analysis. Conclusions: According to the present published data, C. pneumoniae infection may increase the risk of lung cancer. However, for its significant publications and heterogeneity among the included studies, the conclusion should be interpreted cautiously.



How to cite this article:
Hua-Feng X, Yue-Ming W, Hong L, Junyi D. A meta-analysis of the association between Chlamydia pneumoniae infection and lung cancer risk.Indian J Cancer 2015;52:112-115


How to cite this URL:
Hua-Feng X, Yue-Ming W, Hong L, Junyi D. A meta-analysis of the association between Chlamydia pneumoniae infection and lung cancer risk. Indian J Cancer [serial online] 2015 [cited 2020 Dec 1 ];52:112-115
Available from: https://www.indianjcancer.com/text.asp?2015/52/6/112/172506


Full Text

 Introduction



As we all known, lung cancer is the leading cause of cancer-related death word wide.[1] It was estimated that

1.4 million deaths related to lung cancer were found in the year 2008.[2] Although the diagnostic and treatment method was developed in the recent 10 years, the morbidity and mortality rate was still on the rise. The mechanism of lung cancer was not fully understood. However, several risk factors for lung cancer was confirmed by experiment or epidemiology study. Smoking status was confirmed as the independent risk factor for developing lung cancer.[3],[4] Moreover, other carcinogenesis for lung cancer was also found such as radon and asbestos exposure, air pollution, second-hand smoking, genetic susceptibility, and chronic bacterial infection. Recently, several studies have evaluated the Chlamydia pneumoniae infection and lung cancer risk.[5],[6] However, for the small number subjects of each study, the results were not conclusive. Thus, we perform this meta-analysis using open published studies to further assess the relationship between C. pneumoniae infection and lung cancer risk.

 Materials and Methods



Search strategy

We searched the electronic databases of Medline, EMBSE, Web of Science, and China National Knowledge Infrastructure (CNKI) databases for publications related to the association between pneumonia infection and lung cancer risk. The search terms were “lung cancer/carcinoma of the lung” and “C. pneumoniae.” The study objects were limited to human beings, with the language restriction of English and Chinese. All potential relevant studies were assessed in detail, and additional all citations of the included articles were further evaluated in order to identify additional suitable studies. The inclusion criteria were: (1) Study design was limited to prospective cohort study or retrospective case–control study; (2) the patients were pathology clinical confirmed lung cancer; (3) the controls were relative healthy people with no diagnosis of any cancer; (4) the C. pneumoniae infection rate can be extracted from the included individual study. The data were extracted by two reviewers (Xu Hua-Feng, Wu Yue-Ming) independently from all included studies. The year of publication, the first author name, the study design, and the positive number of C. pneumoniae infection were extracted from the included studies.

Statistical analysis

Stata/SE 11.0 (Stata Corporation, College Station, TX, USA) software was used to deal with the data analysis. The odds ratio (OR) was calculated for evaluated the correlation between C. pneumoniae infection and lung cancer risk. The heterogeneity among the included 13 publications was assessed by Chi-square test. The DerSimonian-Laird random effects method for pooling the OR was used if significant heterogeneity was found. Otherwise, the fixed effect model was applied. The publication bias was detected by funnel plot and Egger's line regression test.[7]

 Results



Main characteristics of the included 13 publications

We searched the electronic databases of Medline, EMBSE, Web of Science, and CNKI databases for publications to include in this meta-analysis. Finally, 13 publications involving 2549 lung cancer patients and 2764 controls were included in this meta-analysis. For the included 13 studies, 4 studies were published in Chinese, and other 9 papers were published in English. For the study design, 4 papers are nest case–control, and other 9 are case–control studies. The serum IgA positive rate for C. pneumoniae infection rate ranges from 25.9% to 86.3% for the lung cancer groups and 6.8% to 71.2% for the healthy control group. The main characteristics of included publications are showed in [Table 1].{Table 1}

Results from the meta-analysis

Twelve studies reported the association between C. pneumoniae infection and lung cancer risk by using the serum IgA. The pooled results indicated that the C. pneumoniae infection significant increased the risk of lung cancer OR = 2.07 (95% confidence interval [CI]:

1.43–2.99) [Figure 1] by random effect model. And for serum IgG, 12 publications reported the IgG positive rate in lung cancer patients and relative healthy controls. The pooled OR was 2.22 (95% CI: 1.41–3.50) [Figure 1] by using the random effects model, which indicated that the IgG positive rate was significantly higher in lung cancer patients than that of healthy controls. These results demonstrated that C. pneumoniae infection was significantly correlated with the lung cancer.{Figure 1}

Sensitivity analysis

A single publication involved in the meta-analysis was omitting each time to reflect the influence of the individual data set to the pooled ORs. The OR ranged from 1.20 (95% CI: 1.13–1.28) to 1.31 (95% CI: 1.22–1.40) for IgA [Figure 2] and 1.09 (95% CI: 1.05–1.46) to 1.19 (95% CI: 1.14–1.25) for IgG [Figure 3] with only a slight change. The sensitivity analysis indicated the pooled OR was not sensitive to a single study, which demonstrated that the results were relative stable.{Figure 2}{Figure 3}

Publication bias

Begger's funnel plot and Egger's line regression tests were used to evaluate the publication bias of this meta-analysis.[7] The Begger's funnel plot [Figure 4] and [Figure 5] showed obvious asymmetry. Moreover, Egger's line regression test also indicated significant publication bias (P < 0.05).{Figure 4}{Figure 5}

k

Lung cancer is still the deadliest cancer worldwide despite improvements in diagnostic and therapeutic techniques for the recent several years. Moreover, full understanding of carcinogenesis for lung cancer was not reached. The independent risk factor for lung cancer is smoking which has been confirm by several experiment studies or epidemiology studies in the past several decades.[18] However, other risk factors such as bacterial infection, radon exposure, and genetic susceptibility were not absolutely confirmed.

In 1997, Laurila et al.[17] first hypothesized that C. pneumoniae might correlate with increased risk of lung cancer based on an observation case–control study. Thereafter, several studies were conducted to further evaluate the association between C. pneumoniae infection and lung cancer risk. However, for weak statistical power, the results have been inconsistent. Meta-analysis is a powerful tool for studying cumulative data from individual studies with small sample sizes and low statistical power.[19] Pooling the effects from individual studies by a meta-analysis may increase the statistical power and can help detect modest risk differences among study groups. Thus, we perform this meta-analysis through pooling the publication data. In our meta-analysis, we finally included 13 articles with 4 published in Chinese and 9 published in English. The pooled results showed that the C. pneumoniae infection significant increased the risk of lung cancer OR = 2.07 by random effect model for IgA. And for serum IgG, the pooled OR was 2.22 (95% CI: 1.41–3.50) by using the random effects model which indicated that the IgG positive rate was significant higher in lung cancer patients than that of healthy controls. Both using the IgA and IgG as the C. pneumoniae infection diagnosis method, the significance for infection and lung cancer risk was observed.

We also conducted the sensitivity analysis by deleting each individual study to further assess the OR. We found that the pooled OR was not sensitive to a single study which indicated the result was stable. However, the publication analysis indicated significant publication bias by Begger's funnel plot and Egger's line regression analysis. Hence, we believe that according to the present published data, C. pneumoniae infection may increase the risk of lung cancer. However, for its significant publications bias and heterogeneity among the included studies, the conclusion should be interpreted cautiously.

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