The article reviews the role of microRNAs (miRNAs) in cancer, highlighting their critical role in gene expression regulation and their dysregulation in various cancers. MiRNAs are small non-coding RNAs that target and silence target mRNAs, and their expression can be regulated by genetic and epigenetic mechanisms. The biogenesis of miRNAs involves several steps, including the processing of primary miRNA (pri-miRNA) by the Microprocessor complex (DROSHA and DGCR8), export of pre-miRNA to the cytoplasm by exportin 5, and cleavage of pre-miRNA by DICER1 to form mature miRNAs. Genetic and epigenetic alterations in components of the miRNA biogenesis machinery, such as DROSHA, DICER1, and TRBP, are associated with cancer progression and poor clinical outcomes. Additionally, dysregulation of miRNA expression through transcriptional and epigenetic mechanisms, as well as the reactivation of embryonic pathways controlled by LIN28 proteins, contribute to miRNA dysregulation in cancer. The article also discusses the role of miRNAs in maintaining differentiated cell states and their potential as therapeutic targets.The article reviews the role of microRNAs (miRNAs) in cancer, highlighting their critical role in gene expression regulation and their dysregulation in various cancers. MiRNAs are small non-coding RNAs that target and silence target mRNAs, and their expression can be regulated by genetic and epigenetic mechanisms. The biogenesis of miRNAs involves several steps, including the processing of primary miRNA (pri-miRNA) by the Microprocessor complex (DROSHA and DGCR8), export of pre-miRNA to the cytoplasm by exportin 5, and cleavage of pre-miRNA by DICER1 to form mature miRNAs. Genetic and epigenetic alterations in components of the miRNA biogenesis machinery, such as DROSHA, DICER1, and TRBP, are associated with cancer progression and poor clinical outcomes. Additionally, dysregulation of miRNA expression through transcriptional and epigenetic mechanisms, as well as the reactivation of embryonic pathways controlled by LIN28 proteins, contribute to miRNA dysregulation in cancer. The article also discusses the role of miRNAs in maintaining differentiated cell states and their potential as therapeutic targets.