Objective To investigate the value of Leu (CAG)-tRNA fragment(tRF-Leu^CAG) in evaluation of diagnostic efficacy, survival prognosis of lung adenocarcinoma (LAC) and its relationship with clinical features.

Methods The clinicopathological data of 68 pairs of surgically resected LAC tissues and normal adjacent lung tissues were collected. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the relative expression of tRF-Leu^CAG RNA in LAC and adjacent normal tissues (NC); the relationship between the expression level of tRF-Leu^CAG and clinicopathological features was analyzed. The positive expression of tRF-Leu^CAG was detected by RNA in situ molecular hybridization (RISH). Receiver operating characteristic (ROC) curve was used to analyze the diagnostic efficacy of tRF-Leu^CAG for LAC. Kaplan-meier method was used to analyze the 3-year survival curve of LAC patients. Transwell experiment was used to detect the effect of tRF-Leu^CAG on the migration of lung cancer cells.

Results The expression level of tRF-Leu^CAG in the LAC tissues was significantly higher than that in the adjacent normal lung tissues (P < 0.05); the expression level of tRF-Leu^CAG in patients with the lymph node metastasis was significantly higher than that in patients without the lymph node metastasis (P < 0.05). The expression level of tRF-Leu^CAG was significantly correlated with the degree of differentiation of LAC and lymph node metastasis (P < 0.05), but had no correlation with age, gender, smoking, tumor diameter, tumor grade and TNM stage (P > 0.05). The positive rate of tRF-Leu^CAG in the LAC tissues was 73.53% (50/68), which was significantly higher than 13.24% (9/68) in the normal adjacent lung tissues (P < 0.05). The ROC curve showed that the diagnostic efficacy indexes of tRF-Leu^CAG and carcinoembryonic antigen (CEA) in LAC were as follows. The area under the curve (AUC) was 0.869 and 0.852, 95%CI was 0.806 to 0.926 and 0.794 to 0.910, sensitivity was 86.2% and 83.6%, specificity was 80.5% and 85.8%, Youden inde was 0.643 and 0.608, respectively. Of the 68 LAC patients, 53 had high tRF-Leu^CAG expression (increased group) and 15 had normal and low tRF-Leu^CAG expression (normal and decreased group); the 3-year overall survival (OS) in the increased group was significantly shorter than that in the normal and decreased groups, and the difference was statistically significant (HR=2.968; 95%CI, 1.669 to 5.277; P < 0.05). Transwell migration experiment showed that overexpression of tRF-Leu^CAG promoted the migration of lung cancer cells, while decreased expression of tRF-Leu^CAG inhibited the migration of lung cancer cells (P < 0.05).

Conclusion The tRF-Leu^CAG may be a new oncogene, which can promote the differentiation and metastasis of lung cancer cells, and provide a targeted experimental basis for tRF-Leu^CAG in the treatment of metastatic LAC. The tRF-Leu^CAG may also serve as a new biomarker for the diagnosis and survival prognosis of LAC in the future.