Epigenetic roles of PIWI‑interacting RNAs (piRNAs) in cancer metastasis (Review).

P‑element‑induced wimpy testis (PIWI)‑interacting RNAs (piRNAs) are epigenetic‑related short ncRNAs that participate in chromatin regulation, transposon silencing, and modification of specific gene sites. These epigenetic factors or alterations are also involved in the growth of a variety of human cancers, including lung, breast, and colon cancer. Accumulating evidence has revealed that tumor metastasis and invasion involve genetic and epigenetic factors. Cancer metastasis is characterized by epigenetic alterations including DNA methylation and histone modification. Changes in DNA methylation, H3K9me3 heterochromatin and transposable elements have been detected in several cancers. piRNAs may function in gene silencing and gene modification upstream or downstream of oncogenes in cancer cell lines or cancer tissues. In addition to piRNAs, PIWI proteins can be used as biomarkers for prognosis, diagnosis and clinical evaluation and may be factors in cancer metastasis. Here, we elucidated the possible mechanisms by which piRNAs regulate cancer metastasis, including but not restricted to influencing DNA and histone methylation and transposable elements.