Circulating tumor DNA as a marker of minimal residual disease in non-small cell lung cancer

Circulating tumor DNA (ctDNA) refers to small fragments of nucleic acid (approximately 166 base pairs) that are not associated with cells or cell fragments and circulate in the bloodstream. Circulating tumor DNA has been proven to be a marker of minimal residual disease (MRD), a tumor process that cannot be detected using routine investigations. Circulating tumor DNA can be used as a marker of MRD because tumor cells secrete their DNA into the blood during necrosis, apoptosis, and functioning (with extracellular vesicles, etc.); therefore, it is possible to detect it and identify MRD. Circulating tumor DNA accounts for 0,01% to several percent of all circulating extracellular DNA depending on the size of the tumor, its vascularization and biological properties. Currently, much attention is paid to the detection of minimal residual disease after radical surgery for non-small cell lung cancer (NSCLC), since a number of large studies have shown postoperative plasma ctDNA to be a negative prognostic sign. For example, Chaudhuri et al. showed that 36-month relapse-free survival (RFS) in patients with and without postoperative plasma ctDNA was nearly 0% and 90-99%, respectively. The status of MRD determined by postoperative plasma ctDNA levels may be potentially used for adjuvant treatment selection in the postoperative period. In the DYNAMIC study, MRD-positive patients (with postoperative plasma ctDNA) who received adjuvant therapy had an RFS of 22,4 months while those who did not receive adjuvant treatment had an RFS of 9,3 months. Thus, the status of MRD based on the plasma ctDNA level after radical surgery may allow a personalized treatment approach for patients undergoing radical surgery for non-small cell lung cancer (NSCLC).