PIR and breast carcinoma: It is noteworthy that piR-651 and piR-823 were found to be dysregulated in gastric cancer [43, 44], and moreover, recent study showed a panel of piRNAs are associated with prognosis in breast cancer [28], suggesting that piRNAs which previously considered as “junk” RNAs, are indeed involved in tumor progression and could be used as clinically-relevant biomarkers.