Pursuing sensitive methods for detection and monitoring of oncologic diseases, that would limit the stress for patients, represents a longstanding challenge in cancer diagnostics. As an ideal noninvasive bio-markers may be considered bio-logical molecules that can be detected in blood and that provide most relevant picture about the state and development of disease. In fact, all types of cancer cells carry somatic mutations that enable the cells to escape from regulation and to grow and progress. These mutations are only present in the DNA of tumor cells and thus are hallmarks of cancer cells. Genotyping of tumor tissues becomes a common technique in clinical oncology, but it has its limits. Tissue biopsy only yields information about a very small area of tumor at the time of extraction and in some cases it is difficult or impossible to obtain the tissue sample. Furthermore, it is an invasive method that can stress patients. Analysis of circulating tumor DNA from blood--the so-called liquid biopsy--represents one possible solution. Dying tumor cells release fragments of their DNA into the blood stream. From blood, they can be isolated and subjected to analysis using new, sensitive and precise methods that detect genomic changes. These changes are evolving over time because cancer disease is characterized by evolution and ability to select new mutations that bring growth advantages or resistance to treatment. Our inability to capture the heterogeneity during tumor development is one of the major reasons responsible for failure of cancer treatment. Recent technological progress in detection and characterization of circulating DNA could enable tumor evolution monitoring in real time and become a guideline for an accurate and prompt treatment choice.

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Monitoring of Early Changes of Circulating Tumor DNA in the Plasma of Rectal Cancer Patients Receiving Neoadjuvant Concomitant Chemoradiotherapy: Evaluation for Prognosis and Prediction of Therapeutic Response