Most of the available non invasive biomarkers for the detection of human cancers are reliable in the metastatic disease or able to monitor the primary/ adjuvant chemotherapy for the relapse. Hence, an ideal biomarker especially to detect cancer at an early stage is urgently required to reduce the morbidity and mortality worldwide. microRNAs (miRNA or miR), small non-coding RNAs (18-25 nts) synthesized from the human genome were found to be involved in a variety of cellular processes such as cell proliferation, differentiation and programmed cell death. A unique tissue miRNA expression profile was found in the malignancy of breast, bladder, colon, lung, liver, brain, prostate and pancreas, had proposed their role in the diagnosis of cancer as well as the treatment prognosis. The altered expression was also associated to the metastasis of the cancer cells as well. Among the various methods used for their detection in biological fluid such as blood, urine and saliva, quantitative reverse transcriptase polymerase chain reaction is the most commonly employed technique. Though increasing evidences had suggested the importance of miRNAs, a quality assisted standardized procedure for their detection is fragmentary. Therefore, standardization are urgently needed mainly in the processing of sample, developing a more accurate and precision method along with the normal extracellular housekeeping RNAs which can be used for the normalization to assess the quality and quantity of miRNA. This review article discusses recent update on the role of circulating extracellular miRNA in the diagnosis of human malignancy.

Keywords: Micro RNA; Gene Silencing; Tumor Suppressor Genes; Oncogenes; RNA Interference; Quantitative Reverse Transcriptase Polymerase Chain Reaction; Chronic Lymphocytic Leukemia.