Role of microRNAs in the molecular diagnosis of cancer

MicroRNAs (miRNAs) are evolutionarily conserved, endogenous, small non-coding RNA molecules of about 22 nucleotides in length that function as posttranscriptional gene regulators. They are involved in numerous cellular processes including development, cell differentiation, cell cycle regulation and apoptosis. There is increasing evidence to show that miRNAs are mutated or differentially expressed in many types of cancer and specific functions of the miRNAs are now becoming apparent. Here we discuss the current literature on potential usefulness of miRNAs as diagnostic markers, emphasizing the involvement of specific miRNAs in particular tumor types, highlighting their potential role in distinguishing benign from malignant tissues and/or the different subtypes of the same tumor and/or in diagnosis and classification of tumor of unknown origin.