Lung cancer is the most common cause of cancer deaths worldwide with more than 1.2 million people dying of the disease annually [20, 21]. The study for early detection and treatment of lung cancer is a promising strategy to reduce the mortality of lung cancer. Currently, diagnostic techniques such as spiral computed tomography (CT) and autofluorescence bronchosocopy can detect lung cancers down to the normal range [22, 23]. However, these methods did not improve the 5-year survival rate of lung cancer. An explanation for this poor outcome is that the prognosis for patients with advanced lung cancer remains poor because the cancer is detected at an advanced and typically untreatable stage . Hence, it is very important to investigate some early and more-accurate diagnostic biomarkers for lung cancer to improve the survival rates of patients.
The human NOB1 gene is a newly discovered gene, which is associated with the regulation of cell cycle and cell transcription. And it may participate in occurrence and development of the various tumors by regulating the gene transcription. NOB1 is mainly expressed in the liver, lung and spleen, and downregulated in kidney, prostate, colon and ovarian tissues . Increasing studies indicated that NOB1 has extensive biological functions, for example, it participated in the synthesis and assembling of 26s proteasome and ribosome, regulating cell cycle through the UPP pathway. Besides, NOB1 may be involved in the regulation of cell cycle by ZNRD1 structure domain [25-29].
With the deepening of more and more research, NOB1 is found abnormally expressed in a variety of diseases. Yin et al. found that the NOB1 expression increased with pathological grades and it is important in oral squamous cell carcinoma development and serves as a candidate indicator of aggressiveness and a therapeutic target of OSCC . Besides, NOB1 might be involved in tumorigenesis of prostate cancer, and could be a potential molecular target for prostate cancer gene therapy . However, there are few researches about the NOB1 expression in lung cancer. The study of Li et al.  has provided a basis for our research on the diagnostic value of NOB1 in lung cancer. The results of this study revealed that down-regulation of NOB1 expression using the RNA silencing approach in A549 tumor cells significantly suppressed the proliferation and colony formation ability, and induced tumor apoptosis in vitro. Tumor growth was also suppressed in vivo. Therefore, the above studies showed that although the research about the value of NOB1 in tumors still in the early stage, NOB1 is expected to become a new biomarker with the further study and interpretation. And it may provide a new treatment approach for the patients with lung cancer.
In our study, we investigated the expression level of NOB1 in lung cancer patients and healthy volunteers. The results showed that the level of NOB1 expression was increased in lung cancer samples compared with the levels in healthy controls. Our data also revealed that the expression of this gene is significant correlation with some clinicopathological features in lung cancer patients, including differentiation and invasion depth. In particular, from the analysis of ROC curves, we found that the expression of NOB1 could be used as an efficient diagnostic biomarker for lung cancer patients. Based on the present results and the evidence above, we can speculate that the NOB1 gene may play an important role in lung cancer carcinogenesis and progression.