IsomiRs: A New Approach to Cancer Study

microRNAs are regulatory non-coding RNA molecules that containing about 18-24 nucleotides which involved in critical steps of many cellular processes, specifically gene expression, therefore, their deregulation can lead to human tumorigenesis. some kinds of variants of microRNAs are isomiRs that their length or sequence varies from miRNAs and they commonly araised from diverse cleavage by the ribonucleases Drosha and Dicer. Recent reports confirm that some of isomiRs may be yielded from a miRNA locus, and these physiological mature isomers have important roles in miRNA evolution. In this research, we reviewed new field of miRNAs structural /sequence diversity that can be involved in cancer biology. Also describe the evolutionary approaches and the functional significance of the miRNAs isoforms; however, there are lots of isomiR/miRNA molecular mechanisms that remain unclear. More studies to reveal more insights of functionality isomiRs into the carcinogenesis will provide informative strategies to be used in prognosis, diagnosis or treatment