NDNF and lung adenocarcinoma: In this study, by the PPI and GSEA analysis of each gene within this model, 9 genes referred to RIG-I-like receptor, neuron-derived neurotrophic factors, cancer, and ubiquitin–proteasome system in lung adenocarcinoma, illuminatingly manifesting that the ubiquitin–proteasome system has a potential association with the immune system in cancer.