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The piRNAs (PIWI-interacting RNAs) are ～26-31 nt in length and are very similar to but little longer than the microRNAs (miRNAs) in size [1].Since the discovery of the first piRNA in 2006,the number of piRNA sequences has now reached 173 million from 264 datasets in 21 organisms [2].And,there are 8,438,265 piRNAs identified in the human genome,which far exceeds the total number of miRNAs (～2000) [2],suggesting that piRNAs may play a wide variety of roles in biological activities that remain to be explored.Primarily,piRNAs have been suggested to have functions in transposon silencing by DNA methylation [3].Following that,many functions of piRNAs were reported [1].Of note,early reports claimed the specific expression of piRNAs in the reproduction system [4].However,in recent studies,the expressions of piRNAs in other normal tissues or cancer tissues,such as breast cancer,gastric cancer,colorectal cancer,lung cancer,and liver cancer,have been reported [1].But to date,there is no report demonstrating the expression of piRNA in thyroid and/or in thyroid cancer.