Recent medical breakthroughs in the early 2000s have discovered cell-free DNA as a new diagnostic marker in the circulating blood in humans. As the name implies, cell-free indicates DNA that are found freely in the blood without a nucleus, as DNA is usually found in a cell enclosed in a nucleus. Though cell-free DNA can also be found in the circulatory system of healthy individuals, their concentrations are at very low to negligible concentrations. However studies have found that the concentrations in cancer patients can reach high levels to substantiate diagnostic significance. With numerous studies conducted, it is now a well recognized fact that tumour DNA is liberated into the circulatory system during necrosis and apoptosis.
Furthermore the diagnostic significance of this cell-free DNA is not limited to just cancer patients; as other medical conditions such as graft rejection, stroke, trauma and burns where cellular damage is present, have similar observations too.
Cell-Free DNA can be excreted into the blood stream by both normal and tumour cells usually through either necrosis and/or apoptosis.
Apoptosis is a highly regulated process to “remove” cells that have reached their senescence stage and are replaced by new functionally healthy cells to prevent “over-population” of cells. In an average adult, between 50 and 70 billion cells reach senescence each day and undergo apoptosis. Apoptosis in normal tissues consequentially cleaves DNA into small 185-200bp fragments.
Tumour cells usually undergo necrosis which is an uncontrolled cell death resulting in loss of cell membrane integrity, resulting in the release of DNA fragments in various sizes and can be longer than 200bp.
Early detection has always been a focal point to improve cancer cure rates. Hence there is an increase in interest in looking for assays that can detect Cell-Free DNAthat correlates with specific cancer cells.
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