Circulating micrornas and long noncoding rnas: Liquid biomarkers in thoracic cancers

Thoracic cancers are the leading causes of cancer-related deaths worldwide. Recent advances in genome and transcriptome analysis have allowed for the identification of numerous classes of noncoding RNAs (ncRNAs) that play important roles either in a biological process or human disease. microRNAs (miRNAs) are small, 19–22 nucleotides, ncRNAs that regulate posttranscriptional gene expression by binding to the 3' untranslated region (3'UTR) of their target mRNA. Conversely, long noncoding RNAs (lncRNAs) are a novel class of transcripts longer than 200 nucleotides that do not encode any proteins. Some lncRNAs can interact with miRNAs and act as repressors, impeding them to bind to their protein-coding targets. There is cumulative evidence that these ncRNAs contribute to the tumorigenic process regulating cell growth, apoptosis, and metastasis, and may serve as biomarkers in various types of tumors. In this review, we have summarized the important role of ncRNAs as promising biomarkers in liquid biopsy for the diagnosis and prognosis of thoracic malignancies such as lung cancer, mesothelioma, and thymoma.