Abstract
Lung cancer is the leading cause of cancer-related deaths. Biomarkers for lung cancer have raised great expectations in their clinical applications for early diagnosis, survival, and therapeutic responses. MicroRNAs (miRNAs), a family of short endogenous noncoding RNAs, play critical roles in cell growth, differentiation, and the development of various types of cancers. Current studies have shown that miRNAs are present in the extracellular spaces, packaged into various membrane-bound vesicles. Tumor-specific circulating miRNAs have been developed as early diagnostic biomarkers for lung cancer. Remarkably, some studies have succeeded in discovering circulating miRNAs with prognostic or predictive significance. Extracellular vesicles (EVs), such as exosomes and microvesicles, are recognized as novel tools for cell-cell communication and as biomarkers for various diseases. Their vesicle composition and miRNA content have the ability to transfer biological information to recipient cells and play an important role in cancer metastasis and prognosis. This review provides an in-depth summary of current findings on circulating miRNAs in lung cancer patients used as diagnostic biomarkers. We also discuss the role of EV miRNAs in cell-cell communication and explore the effectiveness of these contents as predictive biomarkers for cancer malignancy.