Since 1948, circulating tumour DNA(ctDNA) was first identified in human blood. ctDNA is in fact DNA shed by tumour cells from all metastatic tumour locations throughout the whole body, and is thrown into the bloodstream and can then be isolated by a standard blood draw. Using this technique scientists can obtain a wide view of tumour heterogeneity, identify different mechanisms of drug resistance, what is its predominance and the clinical rational of precision cancer medicine become a part of our daily practice. Secondly, early detection of cancer may also contribute to global decrease in cancer mortality. Since 1948, circulating tumor DNA (by ctDNA) was first identified in human blood. CtDNA is in fact in shedding tumor cells from all metastatic tumour locations, and is thrown into the bloodstream and can then be isolated by a standard blood draw. Using this technique scientists can obtain a wide view of tumor heterogeneity, identify is mechanisms for drug resistance, what is its predominance and the clinical rational of precision cancer medicine become a part of our daily practice. contribute to global decrease in cancer mortality.