CircRNAs and Axes Involved in Thyroid Cancer based on PTC: A Biomarker for Prognosis, Diagnosis and Treatment

Background: The circular RNAs (circRNAs) are defined as single-stranded RNA molecules with a length of 100 bp up to 4 kb, resulting from head-to-tail junctions at splice sites of spliced transcripts. Moreover, they are stable and abundant conserved RNA molecules, which often have tissue-specific expression and developmental stages. Dysregulation of circRNAs has been identified in many types of malignancies that mainly affect the progression of human cancers. Methods: This review was prepared via searching of the databases of Science Direct, Directory of Open Access Journals (DOAJ), Google Scholar, Pub-Med (NLM), Scopus, Web of Science, and hand searching using relative keywords. The selected papers were fully reviewed and the required information for the review was extracted and summarized. Results: In recent decades, the prevalence of thyroid cancer, especially papillary thyroid cancer (PTC), has increased among all cancers, thereby attracting worldwide attention. The global rate of death from thyroid cancer is approximately 0.2 -0.6 per 100,000 people. Some of the known axes involved in PTC include circ-0025033/miR-1304/miR-1231, circPVT1/miR-126, circBACH2/miR- 139-5p/LMO4, circ-ITCH/miR-22-3p/CBL/β-catenin, circZFR/miR1261/C8orf4, circRAPGEF5/ miR-198/FGFR1, circNUP214/miR-145/ZEB2. In this article, we review briefly the most important signaling axes involved in thyroid cancer. The expression level of microRNA (miRNAs) is regulated by circRNAs. Conclusion: Thus, circRNAs play an important role in the oncogenic and malignant behavior of cancer. The fact that circRNAs have been found in abundance in saliva, exosomes and standard blood samples makes circRNAs a diagnostic marker for diseases, especially cancer.