Modulation of miRNA expression in a tumor. Modulation of the expression of miRNAs can occurs via several distinct strategies. To achieve overexpression of miRNAs (green), miRNA mimics enter tumor cells as “pre” (Top right) or “mature” (Bottom right) miRNA forms. Dicer cleaves pre-miRNAs into short RNA fragments. Subsequently, miRNA forms complex with RISC and Ago2 proteins and binds to DNA to suppress RNA transcription. In contrast, the suppression of miRNA expression in a tumor (blue) can occur via several methodologies, including miR-sponges (top left), and antisense oligonucleotides (middle left) and CRISPR/Cas9 genome editing (bottom left). For genome editing, CRISPR/Cas9 complex enters nucleus and changes DNA sequence of target miRNAs. Both miRNA sponge and antisense oligonucleotides bind to miRNAs and inhibit their functions.