PIWIL1 and cancer: In particular, long ncRNAs (lncRNAs), circular ncRNAs (circRNAs), and small ncRNAs including microRNAs (miRNAs), P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs), and small interfering RNAs (siRNAs) are involved in the regulation of cancer development and progression mostly by regulating gene expression at the transcriptional and post-transcriptional levels via RNA-RNA or RNA-DNA or RNA-protein interactions (Anastasiadou et al., 2017; Romano et al., 2017).