Serial profiling of circulating tumor DNA for optimization of anti-VEGF chemotherapy in metastatic colorectal cancer patients

Understanding the molecular changes in tumors in response to anti-VEGF chemotherapy is crucial for optimization of the treatment strategy for metastatic colorectal cancer. We prospectively investigated changes in the amount and constitution of circulating tumor DNA (ctDNA) in serial peripheral blood samples during chemotherapy. Sixty-one plasma samples taken at different time points (baseline, remission, and post-progression) and pre-treatment tumor samples were collected from 21 patients who received bevacizumab-containing first-line chemotherapy. Extracted DNA was sequenced by next-generation sequencing using a panel of 90 oncogenes. Candidate ctDNAs in plasma were validated using mutational data from matching tumors. ctDNAs encoding one to six trunk mutations were found in all 21 cases, and the mutant allele frequency (MAF) was distributed over a wide range (1-89%). Significant decreases in the MAF at remission and increases in the MAF after progression were observed (p < 0.001). Reduction in the MAF to below 2% in the remission period was strongly associated with better survival (16.6 vs. 32.5 months, p < 0.001). In two cases, mutations (in CREBBP and FBXW7 genes) were newly detected in ctDNA at a low frequency of around 1% in the post-progression period. The use of ctDNA allows elucidation of the tumor clonal repertoire and tumor evolution during anti-VEGF chemotherapy. Changes in ctDNA levels could be useful as predictive biomarkers for survival. Mutations newly detected in ctDNA in the late treatment period might reveal the rise of a minor tumor clone that may show resistance to anti-VEGF therapy.