Jin et al. Journal of Experimental & Clinical Cancer Research 2010, 29:18 http://www.jeccr.com/content/29/1/18 H63D mutations in HCC occurrence still merits study. To clarify the relationship between HFE C282Y and H63D mutations and HCC, a meta-analysis was performed. Methods Study identification and selection Eligible studies were identified by searching the data- bases of PubMed and ISI Web of Knowledge for rele- vant reports published before May 2009. The search criteria “c282y OR h63d” and “liver cancer OR hepato- cellular carcinoma” were used. We also searched reports and dissection databases published in the Chinese Bio- medical database (CBM), China National Knowledge Infrastructure (CNKI), and Wan Fang (Chinese) data- base to collect articles of case-control studies or cohort studies on associations between HFE mutations and sus- ceptibility to HCC before May 2009. The reference lists of the retrieved articles were also reviewed to identify additional articles missed by the above search. Studies were selected if (1) there were available data for at least one of the C282Y and H63D two mutations with risk of HCC using a case-control or cohort design; (2) HCC cases were diagnosed by histopathological biopsy or by elevated AFP and distinct iconography changes (CT, MRI, and B ultrasonography); (3) control subjects were free of cancer. Controls could be com- posed of healthy subjects, chronic liver disease (CLD), including chronic hepatitis (CH) and LC. CLD was either histologically proven or diagnosed based on con- cordant clinical, biological, and morphological criteria. Review articles and articles that did not provide geno- type data were excluded. Data extraction and synthesis The following information was extracted from each study: first author’s surname, year of publication, ethni- city of study population, country where study was con- ducted, and the number of cases and controls for each C282Y and H63D genotype. When specific results were not reported, we used available tabular data to calculate them. Statistical methods To compare the odds ratio (OR) on the same baseline, we used crude OR to conduct the meta-analysis. The effect of association was indicated as crude OR with the corre- sponding 95% confidence intervals (CIs). Because of rela- tively small sample sizes of individual studies and low frequency of variant alleles and the practical clinical value, we performed meta-analysis only in two models: dominant model (YY+CY vs. CC or DD+HD vs. HH) and allele con- trast (Y vs. C or D vs. H). The pooled OR was estimated using the FE model (DerSimonian & Laird) [22]. The Page 2 of 8 heterogeneity between studies was tested using the Q sta- tistic [23]. If P < 0.10, the heterogeneity was considered statistically significant, and the RE model was then used. Heterogeneity was also quantified using the I2 metric, which is independent of the number of studies in the meta-analysis (I2 < 25% = no heterogeneity; I2 = 25-50% = moderate heterogeneity; I2 > 50% = large or extreme het- erogeneity) [24]. The potential small-study bias was tested using the Egger regression test asymmetry [25] and the Begg’s test for funnel plot, which is based on Kendall’s tau [26]. Sensitivity analysis was performed by omitting one study at a time to assess the influence of individual studies on meta-analysis. The distribution of the genotypes in the control group was tested for Hardy-Weinberg equilibrium using a goodness-of-fit Chi-square test. All analyses above were conducted using the STATA version 10.0 software (Stata Corp, College Station, Texas). All P-values were two-sided. A p value less than 0.05 was considered statistically significant. The statistical power was calculated using the PS soft- ware [27]. In order to assess the reliability of the posi- tive association, we calculated false positive report probability (FPRP) [28]. An Excel spreadsheet to calcu- late FPRP is included with the online material http:// jncicancerspectrum.oupjournals.org/jnci/content/vol96/ issue6. If FPRP < 0.20, we think the association is reli- able. Given that the gene mutation was regarded as cau- sal, we used population-attributable risk (PAR) to refer to the proportion of disease risk in a population that can be attributed to the causal effects of the risk allele. PAR can be assessed by using the formula [29]. Results Eligible studies By searching data, we found that 15 articles [7-19,30,31] used case-control or cohort design to explore the rela- tionship between HFE mutation and HCC. Six studies [7,9,13,18,19,30] were excluded either because of insuffi- cient numbers of samples or because they did not pro- vide concrete genotype data. Altogether, nine studies [8,10-12,14-17,31] which contained 1102 cases and 3766 controls met the inclusion criteria and were included in the final analysis. Eight studies were published in Eng- lish and one study was published in Spanish[16]. Five studies [8,12,14,16,17] used peripheral blood leucocytes, two studies used liver tissue [10,31]and two studies used both blood and liver tissue [11,15] to extract genome DNA. All studies used validated methods to genotype the C282Y and or H63D mutation. Seven studies [7-9,11,12,14,16,17,31] used PCR-RFLP, one study [10] used the Taqman method, and one study [15] used PCR combined with 3’minor groove binding group (MGB) probe fluorescent hybridization. Of the nine studies, eight studies (including 958 cases and 2258 controls)