Canonical biogenesis pathway and mechanisms of miRNA deregulation. After RNA polymerse II-dependent transcription, pre-miRNAs are generated from pri-miRNAs or spliced RNA by Drosha-DGCR8 complex or intron splicing pathway, respectively. After exporting to cytoplasm, Dicer digests the pre-miRNAs to the mature miRNAs which guide the miRISC to inhibit target mRNAs. Factors in the yellow box indicate protein regulators or mechanisms leading to the aberrant biogenesis of miRNAs in cancer. See text for more detailed description.