Liquid biopsy: Approaches to dynamic genotyping in cancer

Malignant tumors release tumor cells and fragments of nucleic acids into the bloodstream. Liquid biopsies are non-invasive blood tests that detect circulating tumor cells (CTC) and circulating nucleic acids such as mRNA, microRNA, and cell-free circulating tumor DNA, also known as ctDNA. The presence of ctDNA or CTCs in the plasma has prognostic impact. Since ctDNA contains tumor-specific mutations, its detection in the blood or other body fluids can predict response to treatment and relapse. Moreover, repeated analysis and quantitation of ctDNA can inform about changes in clonal composition over time and thus allow dynamic treatment stratification. Today, the routine clinical use of liquid biopsy diagnostic tests is limited; however, in the near future, they might become commonly used sensitive and specific biomarkers to guide cancer treatment. This review will summarize recent findings on the use of ctDNA for monitoring response to therapy and dynamic genetic treatment stratification.