Hepatocellular carcinoma (HCC) is the sixth most common malignant tumor and the second most common cause of cancer-related deaths among the world (1). On the basis of global cancer statistics, an estimated 782,500 new cases were diagnosed as HCC in 2012, leading to approximately 745,500 deaths of this disease (1). Some risk factors have been showed to be involved in the development of HCC, including hepatitis B virus (HBV), hepatitis C virus (HCV) infection, liver cirrhosis, aflatoxin exposure, and alcohol consumption etc. (2-5).
Studies suggest that epigenetic alterations (DNA methylation, histone modifications, nucleosome positioning and non-coding RNAs) are an early biotic event in human cancers (6,7). As a common epigenetic change, DNA methylation plays an important role in the tumorigenesis, progression and prognosis of cancer (8-10). Mapped to human chromosome 5q21-5q22, the adenomatous polyposis coli (APC) gene, a key tumor suppressor gene (TSG), encodes a large multidomain protein and involves in the Wnt signaling pathway (11,12). Moreover, the APC gene has many biological functions, such as the regulation of cell cycle, cell migration and adhesion, transcriptional activation, apoptosis, and chromosomal instability (13-15). APC promoter methylation has been found in many human cancers, including prostate cancer (16), colorectal cancer (17), breast cancer (18), and HCC (19).
The results with respect to promoter methylation of the APC in HCC vs. benign lesions remains controversial. For example, Harder et al. reported that APC promoter had a same methylation frequency in HCC and liver cirrhosis (20). APC promoter methylation frequency was significantly higher in HCC than in liver cirrhosis by Lee et al. (21). Thus, the current meta-analysis was performed to evaluate the relationship between APC promoter methylation and HCC in cancer vs. liver cirrhosis, chronic hepatitis, and dysplastic nodules. Additionally, we also assessed the correlation between APC promoter methylation and clinicopathological features of patients with HCC, including gender, tumor stage, vascular invasion, HBV, and HCV infection status.
Eligible publications were identified through searching the relevant databases before December 10th, 2016, including the PubMed, Embase, EBSCO and the Cochrane Library. The search strategy was conducted based on the following search terms and key words: (APC OR adenomatous polyposis coli) AND (liver OR hepatocellular OR hepatic) AND (cancer OR tumor OR neoplasm OR carcinoma) AND (methylation OR epigene*). The reference lists from the eligible studies were carefully checked to identify other potential articles.
Eligible articles must fulfil the following selection criteria in this meta-analysis: (I) patients were diagnosed with HCC by histopathological confirmation; (II) studies provided sufficient information to estimate the relationship between APC promoter methylation and HCC in the comparison of cancer and control groups; (III) studies provide sufficient dada to assess the correlation of APC promoter methylation with clinicopathological characteristics in HCC. When authors published several articles using the same sample population, only the most complete publication with more information were selected in our meta-analysis.
Data extraction and quality assessment
Two authors independently extracted the relevant information from the included studies: first author’s surname, year of publication, country, ethnicity, detection method of methylation, sample type, number of patients in case and control groups, methylation level, and clinicopathological parameters such as gender, tumor stage, vascular invasion, HBV, and HCV infection status. Control tissue samples included chronic hepatitis, liver cirrhosis, dysplastic nodules, and normal liver tissues. Additionally, the quality evaluation of the eligible articles was performed using the Newcastle–Ottawa Scale (NOS), ranging from 0 to 9. An individual study with a NOS score of ≥6 was considered as high quality, and a NOS score of ≤3 was considered as low quality (22,23) (Table S1).
The data were analyzed using Stata software (version 12.0, Stata Corporation, College Station, TX, USA). The pooled odds ratios (ORs) with their corresponding 95% confidence intervals (95% CIs) were calculated to determine whether APC promoter methylation was correlated with the risk of HCC in cancer vs. control groups. In addition, the relationship between APC promoter methylation and clinicopathological features of patients with HCC was also analyzed by the combined ORs with the corresponding 95% CIs. The chi-square test and Q statistics were applied to assess the possible heterogeneity among studies (24). The random-effects model was used in the current meta-analysis. If there was obvious evidence of heterogeneity (I2 >50% or P<0.1), a sensitivity analysis was carried out to determine the influence of the pooled OR and the change of heterogeneity by omitting an individual study (25,26). The potential publication bias was carried out using Egger’s test in cancer vs. normal liver tissue samples (27).
A total of 223 relevant publications were searched from a range of online electronic databases as above described (Figure 1). Based on the above selection criteria, 21 available studies (19-21,28-39,40-45) were identified in the current meta-analysis. 16 studies evaluated the relationship between APC promoter methylation and HCC in tissue samples of HCC patients vs. normal live tissues (19-21,28,30,32-35,37,38,40,41,43-45). Three studies evaluated the correlation between APC promoter methylation and HCC in blood samples of HCC patients vs. healthy blood samples (29-31). Six publications analyzed the relationship between APC promoter methylation and HCC in cancer vs. liver cirrhosis (20,21,33,37,39,44). Three publications analyzed the association between APC promoter methylation and HCC in cancer vs. dysplastic nodules (21,33,43), three publications estimated the association between APC promoter methylation and HCC in cancer vs. chronic hepatitis (21,28,37). Nine studies analyzed the correlation between APC promoter methylation and clinicopathological features of patients with HCC (31,33,35-37,39,40,42,44). All eligible articles met a score of more than or equal to 5. The basic characteristics of the included studies are presented in Table S1.
Association between APC promoter methylation and HCC in cancer vs. normal controls
The data included the comparison of 1004 HCC patients and 212 normal live tissues, and 203 HCC patients and 109 healthy blood samples. The results demonstrated that promoter methylation of the APC gene was significantly higher in HCC than in normal live tissues and healthy blood samples (OR =11.46, 95% CI: 5.01–26.21, P<0.001; OR =93.83, 95% CI: 20.33–432.97, P<0.001; respectively) (Figure 2).
Association between APC promoter methylation and HCC in cancer vs. liver cirrhosis, chronic hepatitis, and dysplastic nodules
The result involving 296 patients with HCC and 173 patients with liver cirrhosis showed that APC promoter methylation was significantly higher in HCC than in liver cirrhosis (OR =6.04, 95% CI: 2.59–14.09, P<0.001) (Figure 3).
No significant correlation was observed between APC promoter methylation and HCC in cancer vs. chronic hepatitis and dysplastic nodules (OR =9.51, 95% CI: 0.04–2,387.75, P=0.424; OR =1.36, 95% CI: 0.24–7.66, P=0.728; respectively) (Figure 3), including 151 HCC patients vs. 77 patients with chronic hepatitis and 147 HCC patients vs. 74 patients with dysplastic nodules.
Subgroup analysis of APC promoter methylation in cancer vs. normal live tissues
Table 1 summarizes the pooled OR based on ethnicity (Asians, Caucasians and mixed population) and detection method (MSP and non-MSP). Subgroup analysis by ethnicity showed that APC promoter methylation was associated with an increased risk of HCC in Asian, Caucasian and mixed populations (OR =18.91, 95% CI: 5.26–67.96, P<0.001; OR =7.56, 95% CI: 2.05–27.91, P=0.002; OR =3.73, 95% CI: 1.27–10.99, P=0.017; respectively).
Subgroup analysis based on detection method showed that the pooled OR of APC promoter methylation for the MSP subgroup was 11.48 (95% CI: 2.35–56.16, P=0.003), and 11.38 (95% CI: 5.52–23.46, P<0.001) for the non-MSP subgroup.
Sensitivity analysis in cancer vs. normal live tissues and liver cirrhosis
We conducted a sensitivity analysis to assess the stability of the pooled result based on the omission of one study. When cancer was compared to normal live tissues, we deleted two studies (28,41), and re-calculated the combined OR from the remaining 14 studies (OR =16.60, 95% CI: 8.36–32.96, P<0.001), with a significantly decreased heterogeneity (I2=32.5%, P=0.131).
In the comparison of cancer and liver cirrhosis, one study (21) was removed, the pooled OR from the remaining five studies was 4.40 (95% CI: 2.21–8.78, P<0.001). Meanwhile, there was no substantial evidence of heterogeneity (I2=28.1%, P=0.234).
Association between APC promoter methylation and gender, tumor stage, and vascular invasion status
The results showed that APC promoter methylation was not correlated with gender, tumor stage, and vascular invasion status of patients with HCC (OR =1.33, 95% CI: 0.57–3.08, P=0.51; OR =1.10, 95% CI: 0.36-3.37, P=0.87; OR =0.77, 95% CI: 0.05–12.35, P=0.851; respectively), including 188, 238 and 120 HCC patients, respectively (Figure 4).
Association between APC promoter methylation and HBV and HCV infection status
The result from seven studies with 209 HCC patients demonstrated that APC promoter methylation was significantly correlated with HBV infection status of HCC patients (OR =2.86, 95% CI: 1.38–5.92, P=0.005) (Figure 5).
The result from five studies with 223 HCC patients showed that a significant correlation was found between APC promoter methylation and HCV infection status of HCC patients (OR =3.50, 95% CI: 1.63–7.52, P=0.001) (Figure 5).
Egger’s test was used to detect the potential publication bias in the comparison of cancer and normal live tissues. No obvious evidence of publication bias was found in this meta-analysis (P=0.076>0.05).
Promoter methylation of tumor suppressor genes (TSGs) leads to the downregulation or loss of gene expression (46,47), and may markedly influence the initiation and progression of cancer (48). The reduced expression of the APC gene through promoter methylation has been found in various types of human cancers (49-51). APC promoter methylation may play a crucial role in cancer carcinogenesis and progression (52-55). The promoter of the APC gene has been shown to be frequently methylated in HCC (19,28,30). However, the clinical significance of APC promoter methylation remains unclear. We performed this meta-analysis to evaluate the association between APC promoter methylation and HCC in cancer vs. different benign lesions (liver cirrhosis, chronic hepatitis and dysplastic nodules), and the relationship of APC promoter methylation with clinicopathological characteristics of HCC patients.
Our result showed that APC promoter methylation was significantly higher in tissue samples of patients with HCC than in normal live tissues, suggesting that APC promoter methylation may play a key role in the initiation of HCC. Furthermore, subgroup analyses of ethnicity (Asian, Caucasian and mixed populations) and detection method (MSP and non-MSP) were conducted to find the difference among the different subgroups. A subgroup analysis by ethnicity revealed that APC promoter methylation was correlated with Asian, Caucasian and mixed populations with HCC, indicating that the Asian, Caucasian and mixed populations were susceptible to APC promoter methylation. Moreover, APC promoter methylation was found to be correlated with HCC risk in the MSP and non-MSP, suggesting that the MSP and non-MSP methods were sensitive to the APC gene. Interestingly, in the analysis of blood samples, the result from three studies showed that APC promoter methylation was notably higher in blood samples of HCC patients than in healthy subjects (OR =93.83, P<0.001), which indicated that APC promoter methylation may be a useful noninvasive biomarker based on blood detection. However, the results of subgroup analyses and blood samples should be carefully considered because of small sample sizes.
When HCC was compared to liver cirrhosis, chronic hepatitis, and dysplastic nodules. A significant correlation in the promoter methylation of the APC gene was observed between HCC and liver cirrhosis (OR =6.04, P<0.001), but not between HCC and chronic hepatitis, and dysplastic nodules (P>0.1). Our findings suggested that APC promoter methylation may only contribute to the progression from liver cirrhosis into HCC. Because the sample size in this study is small, more studies with large sample sizes are necessary to further validate the relationship between HCC and chronic hepatitis, and dysplastic nodules for APC promoter methylation.
Finally, the correlation of APC promoter methylation with clinicopathological features of HCC patients was also evaluated. The results revealed that APC promoter methylation was lined to HBV and HCV infection status of patients with HCC (OR =2.86, P=0.005; OR =3.50, P=0.001; respectively), but not associated with tumor stage, gender and vascular invasion status.
Substantial heterogeneity was found in cancer vs. normal live tissues and liver cirrhosis, therefore, the sensitivity analysis was performed in the current meta-analysis. Two studies (28,41) were removed in the comparison of cancer and normal live tissues, and one study (21) was removed in the comparison of cancer and liver cirrhosis. The pooled results remained significant, suggesting the stability of our analyses.
Our results compare favorably with the previous meta-analysis by Zhang et al. (56), which also found that APC promoter methylation was correlated with an increased risk of HCC in cancer vs. normal live tissues. The number of sample sizes included in the current meta-analysis (n=1,216 tissues) was larger than in the previous meta-analysis (n=944 tissues). In addition, the previous meta-analysis did not analyze whether APC promoter methylation was associated with HCC in the MSP and non-MSP subgroups.
Several limitations should be illustrated in this meta-analysis. First, our study mainly included Asian and Caucasian populations, and other ethnic groups, such as African population, were lacking. Second, based on small sample sizes, the relationship of APC promoter methylation with clinicopathological features of patients with HCC should be further studied in the future. Third, the association comparing HCC and liver cirrhosis, chronic hepatitis, or dysplastic nodules is needed in the future. Finally, based on blood samples, additional studies are essential to confirm whether APC promoter methylation may become a potential biomarker using blood samples for HCC diagnosis.
In conclusion, our findings suggest that HCC has a notably higher APC promoter methylation than normal live tissues and liver cirrhosis, but not higher than chronic hepatitis and dysplastic nodules. APC promoter methylation is correlated with HBV and HCV infection status of HCC patients, but not linked to tumor stage, gender and vascular invasion status. APC promoter methylation may be potential noninvasive biomarker in the blood. More well-matched studies with large sample sizes are essential to confirm our findings.
Funding: The research was supported by grants from the Health & Medical Science and Technology Program of Zhejiang Province (2017171691).
Conflicts of Interest: The authors have no conflicts of interest to declare.
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