AIM: To investigate the prognostic value of preoperative lymphocyte-to-monocyte ratio (LMR) in patients with hepatocellular carcinoma (HCC) undergoing curative hepatectomy.

METHODS: Clinicopathological data of 210 hepatitis B virus (HBV)-associated HCC patients who were treated by radical hepatic resection between 2003 and 2010 were retrospectively analyzed. None of the patients received any preoperative anticancer therapy or intraoperative radiofrequency ablation. The diagnosis was confirmed by pathological examination after surgery. Absolute peripheral blood lymphocyte and monocyte counts were derived from serum complete blood cell count before surgery, and LMR was calculated by dividing lymphocyte count by monocyte count. The best cutoff was determined by receiver operating characteristics (ROC) curve analysis. Correlations between LMR levels and clinicopathological features were assessed using the χ² test. Survival outcomes were estimated using the Kaplan-Meier method and compared by the log-rank test. Univariate and multivariate analyses were performed to evaluate the prognostic impact of LMR and other clinicopathological factors on overall survival (OS) and recurrence-free survival (RFS), using the Cox proportional hazards model.

RESULTS: The optimal cutoff value of LMR for survival analysis was 3.23, which resulted in the most appropriate sensitivity of 55.3% and specificity of 74.7%, with the area under the curve (AUC) of 0.66 (95%CI: 0.593-0.725). All patients were dichotomized into either a low (≤ 3.23) LMR group (n = 66) or a high (> 3.23) LMR group (n = 144). A low preoperative LMR level was significantly correlated with the presence of cirrhosis, elevated levels of total bilirubin and larger tumor size. Patients with a low LMR level had significantly reduced 5-year OS (61.9% vs 83.2%, P < 0.001) and RFS (27.8% vs 47.6%, P = 0.009) compared to those with a high LMR level. Multivariate analyses indicated that a lower LMR level was a significantly independent predictor of inferior OS (P = 0.003) and RFS (P = 0.006). Subgroup analysis indicated that survival outcome was significantly more favorable in cirrhotic patients with LMR > 3.23. However, there were no differences between low and high LMR groups for OS and RFS in non-cirrhotic patients.

CONCLUSION: Preoperative LMR was demonstrated for the first time to serve as an independent prognostic factor in HBV-associated HCC patients after curative resection. Prospective studies with larger cohorts for validation are warranted.

Hepatocellular carcinoma (HCC) is one of the leading types of malignant tumors worldwide, which primarily develops in the setting of chronic liver inflammation[1]. In China, nearly 90% of HCC patients have underlying hepatitis B virus (HBV) infection. Hepatic resection has been established as a curative treatment for patients who have localized lesions arising in non-cirrhotic livers, or in cirrhotic livers with well-preserved hepatic function[2]. However, the long-term survival after resection remains dismal due to a high frequency of tumor recurrence[3-5]. Clinicopathological factors, such as microvascular invasion, multifocal disease, tumor size and degree of histologic differentiation, have been used to predict survival in patients with HCC after curative resection[3-6]. However, these clinical tumor parameters can only partially explain the prognostic heterogeneity of HCC.

Cumulative evidence has demonstrated that crosstalk between tumor cells and their surrounding inflammatory microenvironment plays a critical role in the initiation and progression of HCC. Inflammatory infiltrates in the tumor microenvironment can largely influence the biological behavior of HCC[7-12]. Tumor-associated macrophages (TAMs), which comprise a major proportion of leukocytes that infiltrate into the stroma, have been found to promote HCC proliferation, angiogenesis and metastasis[7,11-14]. Immunohistochemical studies have validated the association between high TAM density and unfavorable prognosis in HCC patients after curative resection[15,16]. Peripheral blood monocytes, which are precursors of TAMs[7], have also been reported to be a prognostic factor for HCC[17,18]. Tumor-infiltrating lymphocytes (TILs) are another representative component of the immune microenvironment. Specific TIL subtypes are involved in the clinical course of HCC, and TIL phenotypes are informative regarding prognosis[8-10,13].

Recently, the peripheral blood lymphocyte-to-monocyte ratio (LMR), as a simple surrogate biomarker of TILs and TAMs, has been reported to be a predictor of clinical outcomes in various malignancies[19-25]. LMR also acts as a representative biomarker by combining estimates of host immune homeostasis (i.e., absolute lymphocyte count) and tumor microenvironment (i.e., absolute monocyte count)[19,20]. To date, there have been no reports regarding the prognostic value of LMR in HCC patients. We therefore conducted this study to investigate the impact of preoperative peripheral blood LMR on long-term outcomes after curative hepatic resection for HCC.

Accumulating studies have suggested that the infiltrating inflammatory microenvironment may represent an important determinant for the clinical outcome of HCC[7-12]. The imbalance of inflammatory immune cells, such as TAMs and TILs, in the tumor microenvironment, has been proven to be an important regulator of progression in HCC[11-16]. Systemic inflammatory response can be routinely determined by traditional hematological markers, such as C-reactive protein and neutrophil-to-lymphocyte ratio, which are considered to be valuable prognostic factors in patients with HCC[27-30]. Peripheral blood LMR, as a novel inflammatory biomarker, has been recently investigated and confirmed to be a predictor of clinical outcomes in lymphoma[19,20], colon cancer[21], non-small cell lung cancer[23], nasopharyngeal carcinoma[22], breast cancer[24] and gastric cancer[25].

To the best of our knowledge, this is the first study to investigate the preoperative LMR as a prognostic marker in HCC patients initially treated by curative hepatectomy. Only HBV-related HCC was included to avoid potential confounding factors from different etiologies. An objective and reliable cutoff point for LMR was generated by employing ROC curve analysis. Univariate analysis revealed that patients with an LMR > 3.23 had significantly better OS and RFS than those with an LMR ≤ 3.23. On multivariate analysis, LMR remained an independent prognostic marker for OS and RFS throughout the cohort. These results were consistent with previous findings on other types of tumors, in which a low pretreatment level of LMR was reported as an independent unfavorable prognostic factor[19-25]. However, the cutoff values were cancer-specific in the above studies, possibly reflecting the biologic differences among these studied malignancies.

The association between decreased LMR and poor oncologic outcome is complex and remains to be elucidated. There are several possible reasons accounting for this positive correlation. First, lymphocytes are the basic components of host antitumor immunity, which are important in the destruction of residual cancer cells and related micrometastases[20-22]. They infiltrate into tumor microenvironment and manifest as TILs, both the quantity and the phenotype of which may influence the effectiveness of antitumor immune reaction[8-10]. Unitt et al[8] found that reduced lymphocyte infiltration and a low CD4⁺/CD8⁺ T cell ratio were both significant independent predictors of HCC recurrence following liver transplantation. Two additional studies demonstrated that low intratumoral cytotoxic CD8⁺ T and high intratumoral regulatory T cells were associated with a poorer prognosis in HCC patients after resection[9,10]. In general, peripheral blood lymphocyte count serves as a simple surrogate marker of the host immune status. In our study, an association between a low level of ALC and adverse OS was identified by univariate analysis. We also revealed that patients with a decreased LMR had relative lymphocytopenia, which might be responsible for an incompetent immune response against tumor[20-22].

Second, myeloid-lineage cells, including monocytes and their progeny, are known to have immune suppressive activity[31]. They can also promote tumor angiogenesis, tumor-cell invasion and metastasis[21,31]. Circulating monocytes are recruited to the tumor stroma and differentiate into TAMs. As a major component of tumor microenvironment in HCC, TAMs can interact with cancer cells to enhance tumor progression by producing various cytokines and chemokines[11-15]. Poor clinical outcomes associated with high infiltrations of TAMs have been indicated by Zhu et al[15] and Kong et al[16]. Peripheral blood monocytes may reflect the formation or existence of TAMs[23]. The pro-tumorigenic effect of monocytes on HCC has been associated with poor prognosis, as demonstrated by Sasaki et al[17] and Shen et al[18] and validated in the current study, which showed that monocytosis was associated with poor OS in patients with HCC after resection.

These data indicate that LMR might act as the surrogate marker which reflects the interaction between host immunity (i.e., ALC) and tumor microenvironment (i.e., AMC). The presence of preoperative lymphopenia and monocytosis both served as predictors of inferior OS in our study. However, as the combination of ALC and AMC, LMR provided a better prognostic value. A decreased LMR reflects an inflammatory status that favors tumor progression and impairs host immune surveillance, both of which are associated with poor oncologic outcome. Pretreatment LMR level was also inversely correlated with the presence of liver cirrhosis, and the poor outcome predicted by low LMR level was shown only in cirrhotic patients, not in non-cirrhotic ones. These results indicate that the association between cirrhosis and LMR may be an important mechanism for HCC progression.

LMR is a simple and easily assessable clinical biomarker for prognostic stratification of HBV-associated HCC patients after hepatectomy. However, findings of the current study should be interpreted within its possible limitations. First, formal investigations on the specific components of tumor microenvironment in this population were not performed. Second, due to the retrospective design of the study, selection bias was inevitable, which might have influenced the survival analysis. Third, as the study cohort was comprised of a small single-center sample, we were unable to divide the data set into a training set and a testing set for statistical validation.

In conclusion, our study is the first to demonstrate that preoperative LMR can serve as an independent prognostic factor for patients with HBV-associated HCC undergoing curative resection. As a simple and cost-effective biomarker, LMR could be used to identify HCC patients with a poorer survival, especially those with cirrhotic livers, which may guide postoperative treatment. Future biological studies should further correlate LMR with the tumor microenvironment. Prospective studies with larger cohorts are awaited to validate the clinical usage of LMR as a prognostic marker for HCC patients.

The authors thank the surgeons and nurses in the Department of Liver Surgery, The Third Affiliated Hospital of Sun Yat-sen University for their help in treating the patients in this study.