# Oncogenic EFNA4 Amplification Promotes Lung Adenocarcinoma Lymph Node Metastasis
## 4 Discussion  
Lung cancer has the highest incidence and mortality among major cancers throughout the world, and LUAD patients account for a large proportion of lung cancer patients. Despite the current multiple therapies, the prognosis and treatment for LUAD patients, particularly for those with lymph node metastasis, remain poor, and new therapeutic targets need to be identified. Therefore, the purpose of the current study was to identify and validate genes that are involved in the progression of metastatic LUAD.  
Based on the above starting points, we have three main findings. First, this study provides the first bioinformatics and also experimentally validated link between _EFNA4_ and lymph node metastases in lung cancer. Second, our experimental evidence suggests that _EFNA4_ may be an important player in lymph node metastasis, and targeting this protein represents a method to treat lung cancer. An anti-ephrin-A4 antibody-drug conjugate, PF-06647263, achieved sustained tumor regression in triple-negative breast and ovarian tumor-initiating cells [34]. However, in a phase I study, patients treated with PF-06647263 showed limited response [35]. This result demonstrates the complexity of _EFNA4_ in tumor therapy. On the one hand, targeting EFNA4 does show anti-tumor activity; on the other hand, patients show limited responses and numerous side effects. Therefore, we still need to explore the application scene and molecular mechanisms of _EFNA4_. Third, EFNA4 could be a prognostic marker which can be used to evaluate a lung cancer patient's clinical outcome.  
A limitation of this study is the lack of molecular mechanisms by which EFNA4 promotes lung cancer metastasis. The present evidence indicates that signaling by EPHA2 and its ligand, EFNA4, promotes hepatocellular carcinoma cell migration and the combination of EFNA4 and EPHA10 promotes proliferation and migration in oral squamous cell carcinoma cells [25; 26]. In fact, during the study, we also found the positive relationships between EFNA4 and key glycolytic enzymes (not shown in this paper). In addition to glycolysis, EFNA4-high tumor cells are more metabolically active than EFNA4-low tumor cells in many other metabolic pathways, including the tricarboxylic acid cycle, oxidative phosphorylation, fatty acid metabolism, and so on. Further works are needed to explain the relationship between EFNA4 and metabolic reprogramming in tumors. Based on cancer genomic analysis, EFNA4 overexpression is associated with lung cancer lymph node metastasis. Direct experimental evidence demonstrating the function of EFNA4 in lung cancer lymph node metastasis is still lacking.  
Overall, here, we show that the up-regulation of _EFNA4_ could promote the cell growth, migration and adhesion of lung tumor cells, whereas the down-regulation of _EFNA4_ led to the opposite results. Additionally, tumor survival analysis revealed significant impact of _EFNA4_ expression on survival, and _EFNA4_ overexpression is linked to poorer lung cancer outcome. Our work suggests that EFNA4 could be targeted by therapeutic agents and be a prognostic marker for lung cancer.