PIWIL4 and hepatocellular carcinoma: In this study, we investigated in detail the behavior of a new family of regulatory RNAs, piRNAs, in 14 cirrhotic and 20 matched HCC samples and thereby identified > 700 known piRNAs and 900 novel piRNA-likes expressed in human liver, indicating that PIWI-piRNAs system is active in benign and neoplastic tissues of this organ.