Recently, microRNAs (miRNAs) have emerged as a new type of cancer-specific biomarker. miRNAs are small (~22bp) highly conserved non-coding RNAs endogenously expressed in every cell type. They function as key regulators of gene expression by silencing target transcripts through base-pair complementation.
miRNAs can be secreted from cells and are found in a variety of body fluids including blood, saliva and urine, where they are quantifiable and extremely stable. For these reasons miRNAs are becoming ideal candidates as non-invasive biomarkers for potentially any human disease, including cancer (Schwarzenbach et al., 2014).
Driven by the importance of early cancer diagnosis and the need to distinguish between numerous cancer types, oncologists are leading the way in identifying and validating miRNA signatures to diagnose and monitor disease. Here we highlight recent promising results for lung cancer, breast cancer and prostate cancer.
miRNA biomarkers for early diagnosis of lung cancer
Lung cancer is notoriously difficult to detect in its early stages, therefore there is a real need for biomarkers for its diagnosis. A recent study performed genome-wide miRNA expression profiling in plasma samples of patients with non-small cell lung cancer (NSCLC), a form of the disease that accounts for up to 85% of all lung cancer cases (Wozniak et al., 2015).
The researchers identified a signature of 24 circulating miRNAs in plasma of early stage NSCLC patients that displayed high diagnostic value. This was one of the largest exploratory studies, profiling 754 miRNAs in 100 NSCLC patients, thus providing a strong and highly predictive miRNA signature obtained through rigorous statistical approaches.
Recent research has taken an extra step towards the clinic by taking potential miRNA biomarkers and trialing them in large-scale validation studies. Montani et al. (2015), used participants from the Continuous Observation of Smoking Subjects lung cancer screening program to test a 13-miRNA signature.
They found that monitoring this combination of miRNAs could detect the disease with an overall accuracy of 74.9%. These promising results mean that early detection of lung cancer is now that little bit closer.
miRNA biomarkers to predict prostate cancer
Prostate cancer accounts for almost 15% of all new cancers in men. Is it possible, therefore, to use circulating miRNAs to predict the risk of treatment failure for prostate cancer? This is what Singh et al. (2015) set out to investigate by profiling serum miRNA expression in prostate cancer patients that underwent radical prostatectomy.
The study initially identified a panel of 43 miRNAs that could distinguish between disease stages in 14 prostate cell lines and patient samples. From these, 34 miRNAs were also detectable in the serum of prostate cancer patients. Following validation studies, the researchers concluded that miR-222 and miR-125b were predictors of progression risk in these patients, which could also be used to augment treatment decisions.
A potential miRNA to identify triple negative breast cancer
Triple negative breast cancer (TNBC) is very difficult to treat and accounts for around 20% of all breast cancers in women, so there is an urgent need for biomarkers for early detection of this disease. A recent study used a microarray platform to look at the role of plasma miRNAs in TNBC (Shin et al., 2015).
The researchers identified a five miRNA signature (miR-92a-3p, miR-342-3p, miR-16, miR-21 and miR-199a-5p) that could discriminate TNBC from non-TNBC. Overall, miR-199a-5p showed the highest specificity and sensitivity in distinguishing stage and tumor subtypes, raising hopes that this miRNA might be able to be used for TNBC diagnosis in the future.
Circulating miRNAs have great potential for the diagnosis of cancers where there is an unmet need to be able to diagnose cancers at an early stage or distinguish between cancer types. Their presence in circulating biofluids provides non-invasive ways of establishing early prognosis, predicting treatment response and ascertaining progression risk.
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