What is the biological mechanism by which cancer-derived miRNA appears in urine?

Cancer cells shed their contents into surrounding tissue and circulation through multiple mechanisms: active secretion of exosomes and microvesicles containing miRNA, passive leakage from apoptotic (dying) cancer cells, and active transport of miRNA-protein complexes. These circulating miRNAs enter the bloodstream and are subsequently filtered by the kidneys into urine. Because cancer cells produce significantly more miRNA-containing exosomes than normal cells, and because the kidneys filter large volumes of blood daily, even small tumors can produce detectable elevations in urinary miRNA. Yenos Analytical has confirmed that this filtration process does not disrupt the relative proportions of cancer-associated miRNAs, making urine a faithful mirror of the cancer miRNA signature.