The differential expression of microRNAs between normal and neoplastic tissues has been documented in several tumors . Beside their obvious role in tumor pathogenesis, microRNAs can be exploited as diagnostic markers of malignancy that can be especially helpful for tumors whose histological diagnosis is difficult (e.g., in well differentiated thyroid tumors) . Since microRNAs are very stable, microRNA profiling can be performed not only from frozen, but also from formalin-fixed paraffin-embedded tissues . Apart from tissue microRNAs that can be retrieved from biopsy samples or removed tumors, novel data show that microRNAs can enter the circulation and show significant differences in expression in several forms of malignancy. Circulating microRNAs can thus be envisaged as potential minimally invasive markers of malignancy .