Among these miRNAs, miR-21 has been extensively investigated in different cancers where it was shown to target important tumor suppressors such as, for example, PTEN, SPRY2, TIMP3, PDCD4, RECK, and STAT3, and thus to behave as one of the most important oncogenic miRNAs (oncomiR) identified to date [20]. This evidence concerns the gene PDCD4 and neoplasm.