Small non-coding RNAs, are quickly becoming cornerstones in disease diagnosis and therapy, including microRNAs (miRNA) being discovered as potent biomarkers for a number of tumors. A paper published in Molecules this month looks into the possibility of miRNAs becoming a sensitive, reliable and non-invasive diagnostic and prognostic tool for cancer in the near future.
miRNAs are small RNA molecules that never get translated into protein – instead, they regulate the function of other genes and proteins in the cell, and have been found to play a major role in complex cellular pathways, including those involved in disease.
In terms of carcinogenesis, different miRNAs have been found to act either as oncogenes or tumor suppressor genes. Moreover, various tumors seem to express signature miRNA, which can be easily detected through a biopsy or a blood test, since cancer cells have been shown to shed these molecules into the blood stream and other bodily fluids.
Once in the blood, miRNAs seem to be protected from degradation by external enzymes; as such, they could be used as a stable, sensitive and informative biomarker for early stages of the disease.
miRNA screening has shown promising results in identifying cancerous growth in cases where the origin and type of the tumor is unclear after a positive blood test. In such a way, miRNAs could potentially discriminate between different tumor types and states, such as metastatic and aggressive cancers versus non-malignant tumors, and help determine prognosis and individual response to treatment in different cancer patients.
Early cancer detection requires a reliable and stable biomarker, which could be routinely measured in a non-invasive manner. In fact, miRNAs have been found in virtually all body fluids, of which more curious examples include tears, breast milk and others. However, most relevant diagnostic samples could be acquired from urine and saliva, which would be a breakthrough for completely non-invasive cancer detection.
Curiously, cancer-specific miRNAs in the blood seems to correlate with tumor size, and are found to return to normal levels after tumor resection. As such, these molecules show sensitivity and specificity beyond that of conventional cancer serum biomarkers, which include cell-free nucleic acids, such as DNA and mRNA.
miRNA signatures have already been established for breast, lung, bladder, pancreatic and other cancers. Pending further investigation, miRNAs could soon be validated as reproducible, reliable and non-invasive biomarkers for early detection, diagnosis and prognosis of cancer.