Liver diseases are a global healthcare burden with estimated 844 million people worldwide suffering from chronic liver diseases and an annual mortality rate of 2 million.1 Two main epithelial cell types in the liver are hepatocytes and biliary cells. Hepatocytes make up the majority of the liver with various functions including protein synthesis, detoxification, bile production, and carbohydrate and lipid metabolism,4 so damages to hepatocytes may severely affect liver’s functions. HCC causes massive necrosis of the hepatocytes resulting in the loss of their physiological functions. Liver cancer is a very common malignant tumor with a complicated pathogenesis and the survival prognosis and the quality of life are the result of interactions of many factors. Early detection and treatment of liver cancer can significantly improve the survival and quality of life for patients with liver cancer. If managed properly, such as surgical removal and radio-chemotherapy, patients with late stage liver cancer may enjoy a prolonged life time and reasonable quality of life. Therefore, this study has aimed at investigating potential risk factors which affect prognosis before surgery that may provide a comprehensive guidance to clinicians in their making appropriate surgical approaches and postoperative treatment strategies.
Stat3 signaling pathway is a pro-inflammatory pathway that has been shown to be involved in chronic inflammation, autoimmunity, infectious diseases and cancer, and the members of the pathway are often used as diagnostic or prognostic indicators of disease activity and response to therapy.5 IL-6 is an upstream molecule capable of activating Stat3 pathway and IL-17 is a downstream molecule that is expressed in response to the activation of Stat3.
The present study has shown that IL-6 is highly expressed in paracancerous tissues (Table 2). Table 3 shows that the expression of IL-6 is inversely correlated with the cell differentiation of HCC. A previous study of HCC has shown that HCC tissues expressing lower IL-6 levels are correlated with a better prognosis, longer overall survival, and longer time to recurrence,6 somewhat similar to the results in this study.
On the other hand, there is growing evidence that IL-17 has an important contextual and tissue-dependent role in maintaining health in response to injury, physiological stress, and infection.7 IL-17 is not only associated with the immunity of the body,7 but its role in the development of tumors has also become a focus of research. Similar to IL-6, the current study shows that expressed IL-17 is higher in paracancerous tissues than in HCC tissues (Table 2). Again as shown in Table 3, IL-17 expression is inversely associated with the cell differentiation of HCC. Thus far, published reports support a pathogenic role of IL-17 in cancer development including cancers of the colon,8 the skin,9 the pancrea,10 the hepatocytes,11 the lung,12 and multiple myeloma.13 Patients with UCC may experience a poorer survival prognosis and a higher degree of infiltration of lymphocytes if IL-17 is highly expressed.11,14
Several reports have suggested that over-activated Stat3 is present in a variety of tumor cells and immune cells, suggesting that over-activated Stat3 may influence the body's ability to generate an effective immune response, thereby participate in tumor formation and promote tumor cell proliferation, migration, differentiation, and metastasis.15,16 The present study shows a higher level of activated p-Stat3 in HCC tissues (Table 2) in keeping with the abovementioned reports. In addition, studies have shown that esophageal squamous cell carcinoma and adenocarcinoma have higher IHC scores for p-Stat3 in tumor tissues when cancer cells have higher migration and proliferation.17 Furthermore, activated Stat3 can bind to the promoter region of the SKp2 gene which is a proto-oncogene associated with cervical carcinogenesis.18 In summary, IL-6/Stat3/IL-17 pathway forms a cascade that has been indicated to play an important role in the development, progression and prognosis of several cancers including HCC.19 In this context, the current study warrants further investigations as to the detailed mechanism(s) of the Stat3 pathway in the pathogenesis and prognosis of cancer.
Testing of blood liver enzymes is routinely performed and changes in levels of aminotransferases are important diagnostic indicators revealing detrimental impacts to hepatocytes, therefore, liver functions. For example, elevated levels of ALT and AST may indicate hepatocyte-dominated disease, while elevated levels of ALP and GGT may suggest cholestasis-dominated disease.20 The sources of AST can be multiple organs including liver, heart, skeletal muscles, kidneys, brain, or red blood cells.21,22 However, ALT are more specifically derived from the liver and therefore is the preferred clinical test for diagnosing liver disease. GGT is a membrane-bound enzyme that is a key enzyme in biotransformation, nucleic acid metabolism, catalyzing the degradation of extracellular glutathione (GSH). GSH is critical in protecting cells from oxidant-induced damage produced during normal metabolism.23 ALP is a hydrolytic enzyme that is widely present in hepatocytes and blood sinuses of the bile duct membrane and is associated with the uptake and transport of certain substances. Elevated serum levels of ALP are associated with liver diseases including HCC, cholangiocarcinoma, and biliary cirrhosis.24 A previous case-control study has found that blood levels of GGT, ALT, and AST are elevated in approximately 90% of cases liver cancer, while half of the cases also show elevated levels of liver-specific ALP or bilirubin.25
A retrospective study has investigated the relationship of ALT, AST, GGT and ALP with HCC among patients who underwent hepatectomy and found that ALT, AST, GGT and ALP are positively associated with the risk of HCC and, GGT and AST/ALT are independent risk factors predicting postoperative survival in patients with primary HCC.8 These observations are consistent with our findings presented here. Due to the role of GGT in the degradation of glutathione (GSH), GGT has been associated with oxidative stress which may induce a microenvironment that promotes tumor growth in the liver.26 There is also evidence of elevated GGT in patients with obesity or diabetes or hepatic steatosis27 which are associated with metabolic syndrome that it is itself associated with an increased risk of HCC.28
Having validated the patient cohort using conventional TNM clinical staging to predict survival prognosis among HCC patients, we have analyzed and found that elevated levels of all 4 enzymes are correlated with poor survival among these HCC patients (Figure. 2). To investigate individual ability of these enzymes in survival prediction, we have adopted AUC (area under the curve) for this purpose. AUC reflects the ability in predicting survival by which the larger a factor’s AUC is, the higher its predictive ability is. As shown in Figure. 3, among ALT, AST, GGT and ALP enzymes, ALP shows the highest AUC of 0.708, suggesting its greatest ability to predict postoperative survival and the quality of life in patients with HCC. The above conclusion is confirmed by multifactorial COX regression analysis which reveals elevated levels of ALP are an independent risk factor for postoperative survival in HCC patients (Table 4). Quantifying prediction ability for individual enzyme is advantageous because clinicians can judge the reliability of a risk factor used in their survival analyses.
A novel approach in this study is the combinational analysis of multiple bio-factors that can be able to increase AUC values. For example, a 5-factor combination of ALT + AST + ALP + IL-17 + p-Stat3 shows significantly larger AUC value (0.826) than a 2-factor combination of AST + ALP (AUC = 0.787), suggesting a higher predicting power (Table 5). This approach is significant in that clinicians may use multiple routinely tested factors to reliably predict 5-year survival preoperatively before surgery.
In summary, we have shown 3 major findings in this investigation: (1) IL-6/Stat3/IL-17 signaling pathway is involved in survival prognosis among HCC patients; (2) Liver function-related aminotransferases ALT, AST, GGT and ALP can predict survival prognosis for HCC patients before surgery; and (3) A novel approach of combining multiple risk factors can be used to better predict HCC patients’ survival prognosis and quantifying prediction power using ROC analysis (AUC values) for individual risk factors may facilitate clinicians to judge the reliability of survival analyses. Utilizing routinely tested clinical bio-indicators to predict potential survival prognosis before surgery is significant in terms of facilitating surgeons’ decision-making for personalized surgical approaches as well as appropriate radio-chemotherapy after surgery. However, to establish a clinically practical protocol, e.g., the cutoff values for serum levels of individual enzymes for survival predictions to be used as clinicians’ guiding reference, requires a much larger sample of HCC patients. Our ongoing investigation is aimed at organizing a multi-center collaboration study to accomplish the above goal.