ABSTRACT
Cancer is one of the common causes of deaths worldwide. Despite advances in cancer treatment, mortality and morbidity remains high, since most tumors are diagnosed at advanced=incurable stages. Therefore, there is a great need for novel methods that can detect cancer at an early stage. Evaluation of molecular changes in tumor cells in combination with the existing detection methods may help in early detection of cancer. Cancer biomarker is any biological substance that is indicative of the presence of the tumor in the body. It can be derived from the tumor site, remote media or found in circulation. Cancer biomarkers include cell-free tumor derived DNA, RNA, and protein. Elevated levels of DNA have been detected in serum and plasma of cancer patients using quantitative PCR [1-4]. Hence, quantitation of cell-free DNA may be useful in tumor diagnosis. In addition, DNA methylation markers have been used to detect epigenetic changes in cancer. Changes in gene expression contribute to cancer initiation and progression. Reverse transcriptase PCR (RTPCR) has been used to detect alterations in gene expression patterns. With the advent of microarray technologies, gene expression profiling studies have been carried out using circulating RNA and RNA from remote media [5,6]. Use of RNA as a biomarker is challenging due to decreased stability of the molecule. Proteins secreted by tumor cells into the extracellular environment may also be used as a biomarker in cancer diagnostics [7,8]. However, acquiring proteomic data has been challenged by lack of standardized methodologies, sensitivity, and reproducibility due to tumor heterogeneity.
