Introduction:
The finding that long noncoding RNAs (lncRNAs) originating from tumor cells could be found in general circulation has prompted the idea to use lncRNAs as noninvasive diagnostic biomarkers of particular diseases. In this study we explored the expression pattern of circulating GAS5 (growth arrest-specific transcript 5) lncRNA in non-small cell lung cancer (NSCLC) patients and its association with clinicopathological characteristics.

Material and methods:
Expression pattern of circulating GAS5 was analyzed in 58 plasma samples of NSCLC patients, and 15 healthy controls. Quantitative assessment was performed using the real-time PCR method and TaqMan chemistry.

Results:
Circulating GAS5 expression level in NSCLC patients was not significantly decreased compared to control samples (p = 0.081). Statistically significant difference in GAS5 expression was found in relation to TNM stage of the tumor (p < 0.001), decreasing with progression of the tumor stage. Lower GAS5 expression was detected in patients with larger tumors (p = 0.006), and in patients with lymph node metastasis (p = 0.001). Receiver operating characteristic curve analysis was used to evaluate the diagnostic potential of circulating GAS5 expression, showing the highest predictive power in distinguishing between stage III/IV patients and control samples (AUC = 0.8; sensitivity 53%, specificity 93%), and also for separating patients between TNM stage I/II and stage III/IV (AUC = 0.82; sensitivity 73%, specificity 79%).

Conclusions:
Our study suggests that decreased expression of circulating GAS5 is closely related to the tumor size and TNM stage. Therefore the measurement of GAS5 expression level in plasma could be a promising noninvasive diagnostic molecular biomarker in NSCLC patients.