PIR and colorectal cancer: [65] PiRNAs are highly abundant in human plasma [63] Plasma levels of PiR-019825 were found to be deregulated in patients with colorectal cancer, whereas piR-016658 and piR-020496 were associated with prostate cancer patients, and plasma levels of piR-001311 and piR-016658 were found to be dysregulated in patients with pancreatic cancer. [63] Despite their large quantities, the role of piRNAs in the circulation has not been studied and still needs to be elucidated.