Prognostic Significance of EZH2 Expression in Non-Small Cell Lung Cancer: A Meta-analysis.

Lung cancer is a leading cause of cancer deaths in the world. Approximately 80–85% of all lung cancers are non-small-cell lung cancer (NSCLC)1. The prognosis for lung cancer patients is generally poor, with an overall 5 year survival rate of approximately 15%, and it has shown little improvement in recent decades2,3. Several independent prognostic factors for survival have been identified: performance status (PS), disease stage, age, sex and amount of weight lost4. Some of these factors are useful when choosing treatment options for an individual, principally disease stage and PS. However, the discriminant value of most potential prognostic biological markers is insufficient to predict the optimal therapeutic course for an individual5. Enhancer of zeste homolog 2 (EZH2) is a key component of the polycomb repressive complex 2, which possesses histone methyltransferase activity and mediates gene silencing through posttranslational histone modifications6. EZH2 is frequently overexpressed in a wide variety of human malignancies such as breast cancer7, prostate cancer8, gastric cancer9, colorectal cancer10 and lung cancer. In addition, it also promotes cancer development and progression through chromatin modification by epigenetic activation of oncogenic signaling cascades and silencing of tumor suppressor genes, and has been implicated in cell proliferation, differentiation, invasion, and metastasis11. Thus, it is acting with oncogenic properties. Many studies have evaluated whether the overexpression of EZH2 may be a prognostic factor for survival in patients with lung cancer. However, the results of the studies are inconclusive and no consensus has been reached. It is unknown whether differences in these investigations have been mostly due to their limited sample size or genuine heterogeneity. Thus, we conducted a meta-analysis of all available studies relating EZH2 with the clinical outcome in patients with lung cancer.