The expression signature of many miRNAs is specific to cell type and function, and also correlates with common oncogenic features. This specificity is useful as a diagnostic tool in the discrimination of tumor origins, subtypes, and oncogenic mutations. Individual miRNAs can also act as markers of cancer susceptibility; specifically, mutations in miRNAs and their binding sites are commonly associated with increased cancer risk. Furthermore, miRNA-associated mutations and aberrant expression can predict cancer prognosis and response to therapy. These features make miRNAs an appealing tool for clinical use.