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Abstract: MicroRNAs are non-coding ribonucleic acids that are evolutionarily protected. MiRNAs control the expression of genes after transcription by mRNA decomposition or inhibition of their translation. These molecular structures control physiological and pathological processes; therefore, many of them can play vital roles as oncogenes or tumor inhibitors. Besides, the occurrence of various mutations in miRNAs can lead to cancer. In this review article, we want to peruse the role of miR-491-5p in various cancers. In recent years, many experiments and studies have been performed on the involvement of miR-491-5p in cancer, invasion, and cell metastasis. Metastasis is an event that makes cancer more advanced and harder to treat. When cancer is invasive, the cancer cells invade nearby tissues or other organs and develop cancer. Tumor studies have shown that miR-491-5p can inhibit cell growth, invasion, and metastasis. Thus, expression enhancement of miR-491-5p disrupts cell migration and improves cancer.

More powerful prognostic and diagnostic tools are urgently needed for identifying and treating ovarian cancer (OC), which is the most fatal malignancy in women in developed countries. Circular RNAs (circRNAs) are conservative and stable looped molecules that can regulate gene expression by competing with other endogenous microRNA sponges. This discovery provided new insight into novel methods for regulating genes that are involved in many disorders and cancers. This review focuses on the dysregulated expression of circRNAs as well as their diagnostic and prognostic values in OC. We found that studies have identified twenty-one downregulated circRNAs and fifty-seven upregulated ones. The results of these studies confirm that circRNAs might be potent biomarkers with diagnostic, prognostic and therapeutic target value for OC. We also consider the connection between circRNAs and OC cell proliferation, apoptosis, metastasis, and chemotherapy resistance and sensitivity.