Circular RNAs (circRNAs) are an evolutionarily conserved novel class of 
non-coding endogenous RNAs (ncRNAs) found in the eukaryotic transcriptome, 
originally believed to be aberrant RNA splicing by-products with decreased 
functionality. However, recent advances in high-throughput genomic technology 
have allowed circRNAs to be characterized in detail and revealed their role in 
controlling various biological and molecular processes, the most essential being 
gene regulation. Because of the structural stability, high expression, 
availability of microRNA (miRNA) binding sites and tissue-specific expression, 
circRNAs have become hot topic of research in RNA biology. Compared to the 
linear RNA, circRNAs are produced differentially by backsplicing exons or lariat 
introns from a pre-messenger RNA (mRNA) forming a covalently closed loop 
structure missing 3' poly-(A) tail or 5' cap, rendering them immune to 
exonuclease-mediated degradation. Emerging research has identified multifaceted 
roles of circRNAs as miRNA and RNA binding protein (RBP) sponges and 
transcription, translation, and splicing event regulators. CircRNAs have been 
involved in many human illnesses, including cancer and neurodegenerative 
disorders such as Alzheimer's and Parkinson's disease, due to their aberrant 
expression in different pathological conditions. The functional versatility 
exhibited by circRNAs enables them to serve as potential diagnostic or 
predictive biomarkers for various diseases. This review discusses the 
properties, characterization, profiling, and the diverse molecular mechanisms of 
circRNAs and their use as potential therapeutic targets in different human 
malignancies.