Next Generation Sequencing (NGS) is the method which allowed scientists to determine the sequence of the whole human Genome, and such DNA “mapping” can now be performed on circulating cell DNA in the blood – either from circulating (e.g. white – blood) cells or cell-free DNA (cfDNA), derived from dying (“turning-over”) cells – indeed such cfDNA is always entering the bloodstream, with a turnover half life of some minutes, before the body digests and recycles the constituents. What has recently been appreciated is that this last statement applies to cancer – fragments of cancer cfDNA are constantly entering the bloodstream, are detectable by NGS and can be differentiated from normal DNA by the mutational “fingerprint” – best detected by the ‘defining’ gains and losses (DNA Copy Number Instability score – CNI).
Indeed, assessment of CNI may be the best test for determining the presence of cancer, the best test for determining whether treatments such as surgery have achieved a cure of a cancer and whether a past cancer is returning – by serial testing at intervals. More research on the cfDNA may allow us to determine the tissue of origin of the cancer e.g. prostate versus lung cancer, and for following the mutational evolution of a cancer- for cancer cells are mutating unceasingly during their natural history and oncologists nowadays can use drugs to block some specific driving oncogenes pathways-of therapeutic importance.