Aim: To investigate whether neuron-glial antigen 2 (NG2) could be an effective prognostic marker in hepatocellular carcinoma (HCC).
Methods: NG2 expression was semi-quantitatively scored from the immunohistochemistry (IHC) data based on the number of positive cells and the staining intensity. A total of 132 HCC specimens and 96 adjacent noncancerous tissue samples were analyzed by IHC for NG2 protein expression. To confirm the NG2 expression levels observed by IHC, we measured NG2 expression in 30 randomly selected tumor and adjacent noncancerous tissue samples by quantitative real-time polymerase chain reaction and Western blot. The correlations between NG2 protein expression and the clinicopathological features of HCC patients were analyzed using the χ (2) test. To assess the prognostic value of NG2 for HCC, the association between NG2 expression and survival was analyzed using the Kaplan-Meier method with the log-rank test. To further evaluate the prognostic value of NG2 expression, a Cox multivariate proportional hazards regression analysis was performed with all the variables to derive risk estimates related to disease-free and overall survival and to control for confounders.
Results: High NG2 expression was observed in significantly more primary tumor samples (63.6%; 84/132) compared with the adjacent noncancerous tissue samples (28.1%; 27/96) (P < 0.0001). Moreover, high NG2 protein expression was closely associated with tumor differentiation (χ (2) = 9.436, P = 0.0089), recurrence (χ (2) = 5.769, P = 0.0163), tumor-node-metastasis (TNM) stage (χ (2) = 8.976, P = 0.0027), and invasion (χ (2) = 5.476, P = 0.0193). However, no significant relationship was observed between NG2 protein expression in HCC and other parameters, such as age, sex, tumor size, serum alpha fetoprotein (AFP), tumor number, or tumor capsule. The log-rank test indicated a significant difference in the overall survival of HCC patients with high NG2 expression compared with those with low NG2 expression (29.2% vs 9.5%, P < 0.001). Moreover, NG2 expression in HCC tissue significantly correlated with disease-free survival (15.2% vs 6.7%, P < 0.001). Multivariate analysis showed that NG2 expression (HR = 2.035, P = 0.002), serum AFP (HR = 1.903, P = 0.003), TNM stage (HR = 2.039, P = 0.001), and portal vein invasion (HR = 1.938, P = 0.002) were independent prognostic indicators for OS in HCC patients. Furthermore, NG2 expression (HR = 1.974, P = 0.003), serum AFP (HR = 1.767, P = 0.008), TNM stage (HR = 2.078, P = 0.001), tumor capsule (HR = 0.652, P = 0.045), and portal vein invasion (HR = 1.941, P = 0.002) were independent prognostic indicators for DFS in HCC patients.
Conclusion: The up-regulation of NG2 is associated with poor prognosis in HCC. Therefore, NG2 could be useful as an additional prognostic marker to increase the resolution of traditional approaches.
Keywords: Hepatocellular carcinoma; Neuron-glial antigen 2; Poor prognosis; Prognostic marker; Survival analysis.