Clinical Application of Liquid Biopsy in Targeted Therapy ofMetastatic Colorectal Cancer

Colorectal cancers (CRC) shed DNA into blood circulation. There is growing evidence that the analysis of circulatingtumor DNA can be effectively used for monitoring of disease, to track tumor heterogeneity and to evaluate response to treatment.Case Presentation.Here,wedescribetwocasesofpatientswithadvancedCRC.Thefirstcaseisaboutapatientwithnoavailabletissue for analysis of RAS mutation status. Liquid biopsy revealed RAS-wild-type and the therapy with anti-EGFR (epidermalgrowth factor receptor) monoclonal antibody cetuximab could be initiated. In the second case, the mutational profile of a patientwith initial wild-type RAS-status was continually tracked during the course of treatment. An acquired KRAS exon 3 mutation wasdetected. The number of KRAS mutated fragments decreased continuously after the discontinuation of the therapy with EGFR-specific antibodies.Conclusion. Liquid biopsy provides a rapid genotype result, which accurately reproduces the current mutationstatus of tumor tissue. Furthermore, liquid biopsy enables close monitoring of the onset of secondary resistance to anti-EGFRtherapy