The pretreatment lymphocyte to monocyte ratio predicts clinical outcome for patients with hepatocellular carcinoma: A meta-analysis

The lymphocyte-to-monocyte ratio (LMR) has been reported to predict clinical outcomes in multiple malignancies. The aim of this study was to assess the prognostic role of pretreatment LMR in hepatocellular carcinoma (HCC). A total of seven studies comprising 2,738 patients were included in the meta-analysis. Pooled results showed that elevated LMR was significantly associated with increased overall survival (OS) (HR: 0.31, 95% CI: 0.20–0.47, p < 0.001), disease-free survival (DFS)/recurrence-free survival (RFS) (HR: 0.57, 95% CI: 0.49–0.67, p < 0.001). The favorable prognostic impact of high LMR on OS was observed in all subgroup with different sample size, type of publication, NOS score, and the cut-off value of LMR. In addition, low LMR was significantly correlated with TNM stage and BCLC stage. We therefore conclude that elevated pretreatment LMR could be a favorable prognostic factor for clinical outcomes in patients with HCC.

Inclusion criteria. The criteria for inclusion were listed as follows: (1) the diagnosis of HCC were confirmed by pathology; (2) studies assessing the association of pretreatment LMR with OS, DFS/RFS, or CSS; (3) the cut-off value of LMR was reported; and (4) studies supplied sufficient information for calculating hazard ratio (HR) and 95% confidence interval (CI).
Exclusion criteria. The exclusion criteria were as follows: (1) reviews, letters, case reports, and comments; (2) reporting insufficient data for calculating an HR and 95% CI; and (3) overlapping or duplicate data.
Data extraction and Assessment of risk of bias. The two reviewers independently reviewed all eligible studies and extracted data. Any disagreement was resolved by a third reviewer. The following information was captured using data abstraction forms: Study characteristics included first author's name, year of publication, study design (prospective or retrospective), type of publication, country, ethnicity, survival analysis methods (multivariate, univariate), and time of follow-up. Patient characteristics included patient ages and genders, number of patients, disease stage, treatment, and cut-off value. Outcome measures included HRs for OS, DFS, RFS, or CSS as well as their 95% CIs. HRs were extracted from multivariate or univariate analyses or estimated from Kaplan-Meier survival curves 20 .
The study quality was evaluated in accordance with the Newcastle-Ottawa Scale (NOS) 21 . This included an assessment of subject selection, comparability of groups, and clinical outcome. A total of nine items were extracted and each item scored 1. The maximum score is 9 and those studies with a NOS score ≥ 7 were considered as high-quality studies.
Statistical analysis. The meta-analysis was conducted using RevMan 5.3 software (Cochrane Collaboration, Copenhagen, Denmark). Heterogeneity between studies was estimated using Cochrane's Q statistic and I 2 statistic 22 . A p-value < 0.1 for the Q-test or I 2 > 50% indicated significant heterogeneity. When there was no statistically significant heterogeneity, we used the fixed-effects model for pooling the results; otherwise, the random-effects model was applied. HRs and their 95% CIs were searched in the original articles or extrapolated using methods described by Tierney and Parmar 20,23 . The log HR and standard error (SE) were used for aggregation of the survival results 23 . The associations between LMR and clinicopathologic features were expressed as odds ratios (ORs) and its 95% CIs. P < 0.05 was defined as statistically significant. Subgroup analyses were conducted for: the sample size, type of publication, NOS score, and the cut-off value of LMR. Sensitivity analyses were carried out to evaluate result stability excluding each study.

Results
Search results. Our search strategy yielded 63 potentially relevant records. After duplicates removal (21 records), 42 articles were screened for eligibility. Of these, 32 were excluded through titles and abstracts, leaving 10 articles for further evaluation. Subsequently, 3 articles did not meet the inclusion criteria and were therefore excluded. Eventually, seven studies, comprising a total of 2,507 patients, were considered eligible for the present meta-analysis 18,[24][25][26][27][28][29] . The PRISMA flow diagram of the study selection process was shown in Fig. 1.

Characteristics of the included studies.
According to the publication type, 6 and 1 studies were published in full-text and abstract forms, respectively. All included studies were from China and were published between 2014 and 2017. The sample sizes ranged from 208 to 1,020. There were six studies for OS, and all for DFS/ RFS. The cut-off values for LMR ranged from 0.83 to 3.77. All included studies consisted of two groups: high and low LMR. HR and 95% CI was extracted directly from the seven studies. In methodological quality of studies, the NOS scores of the included studies ranged from 5 to 8. Detailed patient characteristics and methodological quality are shown in Table 1.

Meta-analysis. LMR and OS in HCC.
Six of the included studies reported the data of LMR and OS in HCC.
To detect the potential heterogeneity, subgroup analyses stratified by sample size, type of publication, NOS score, and the cut-off value of LMR (Table 2). Subgroup analysis revealed that high LMR predicted increased OS in patient with HCC, regardless of the sample size (≥ 300 and < 300), type of publication (full-text and abstract), NOS score (≥ 7 and < 7), and the cut-off value of LMR (≥ 3 and < 3). LMR and clinicopathological features. To further explore the impact of LMR on the clinical features in HCC, we identified 9 clinical factors in HCC. The pooled analysis demonstrated that low LMR was significantly correlated with TNM stage (III-IV vs. I-II; HR = 1.78, 95% CI: 1.19-2.68, P = 0.005) and BCLC stage (B/C vs. A; HR = 1.70, 95% CI: 1.21-2.39, P = 0.002). Whereas no significant association was found with gender, AFP, liver cirrhosis, tumor differentiation, tumor number, tumor size, and vascular invasion. The correlation between LMR expression and clinicopathological parameters of HCC is shown in Table 3.
Sensitivity analysis. In order to assess the influence of single studies on the overall estimate, the sensitivity analysis was performed. Each single study was removed each time to estimate the influence of individual data sets on the combined HR for OS. The results showed that no study had a significant effect on the observed effect size (pooled HR), indicating the robustness of our findings.

Author
Year Country  25 . In the tumor microenvironment, the inflammatory immune cells have been implicated in HCC progression 30,31 . The pretreatment LMR, as a promising inflammatory biomarker, is reportedly linked to prognosis in patients with HCC 18,19,28 . Therefore, LMR may serve as a promising prognostic factors for HCC patients. To our knowledge, this is the first meta-analysis to investigate the prognostic effect of pretreatment LMR in HCC. Our meta-analysis provides strong evidence that the presence of high LMR significantly increases OS and DFS/RFS in patients with HCC. Stratified analysis demonstrated that high LMR was significantly correlated with increased OS in patient with HCC, regardless of the sample size, type of publication, NOS score, and the cut-off value of LMR. In addition, we further assessed the correlation between pretreatment LMR and clinicopathological features. The pooled data showed low LMR was linked with TNM stage and BCLC stage. Therefore, pretreatment LMR may serve as a promising prognostic biomarker for estimating HCC prognosis. Furthermore, we also performed sensitivity analysis and found that no study had a significant effect on the observed effect size (pooled HR), indicating the robustness of our findings.

Hepatocellular carcinoma (HCC) is mainly caused by viral infections such as hepatitis B virals (HBV) and hepatitis C virals (HCV) 3 . Mounting studies indicated that infiltration of inflammatory cells in the tumor microenvironment significantly affected the biological behavior of HCC
The exact molecular mechanisms responsible for the prognostic impact of LMR in HCC are unclear. It has been suggested that cross-talk between the inflammatory response and tumor progression play a critical role in the initiation and progression of HCC 14,32,33 . In the tumor microenvironment, inflammatory infiltrates have a large influence on the biological behavior of HCC 34,35 . Tumor-infiltrating lymphocytes (TILs), as representative component of the immune microenvironment, are implicated in several stages of HCC progression, and TIL phenotypes may be a predictor for favorable prognosis 36,37 . Conversely, low lymphocyte counts might result in an insufficient immunological reaction, which lead to inferior survival in multiple cancers 38,39 . In addition, infiltrated CD4+ and CD8+ T cells interaction among each other are essential to the antitumor immune response by inducing tumor cell apoptosis 40,41 . Monocytes infiltrating tumor tissue are also involved in HCC development and progression 42 . Activated monocytes in HCC microenvironments can trigger and polarize T-cell responses and faciliate inflammation-induced tumor development 43 . Tumor-associated macrophages (TMAs) are derived from circulating monocytes. TAMs can accelerate HCC cell proliferation, tumor-associated angiogenesis, and metastasis 30,37,44 . Several studies showed that high infiltration of TAMs predicted decreased survival in various    45,46 . Given this background, the observed favorable of high pretreatment LMR on OS of cancer patients may reflect the critical function of LMR in an inflammatory tumor microenvironment that inhibits tumor progression. Nevertheless, there were several limitations to the present study. First, excessive heterogeneity existed among studies. Subgroup analyses didn't find the potential sources of heterogeneity. In addition, we performed sensitivity analysis. The results showed that no study had a significant effect on the observed effect size. Second, the cut-off value for LMR was not unified in each study. Third, all included studies were retrospective analysis. Fourth, all included studies were from China, which limited our conclusions for other ethnic populations.
In conclusion, our findings demonstrated that an elevated pretreatment LMR is associated with favorable outcomes in patients with HCC.   Table 3. Meta-analysis of the association between LMR and clinicopathological features of HCC.