Cetuximab is a chimeric (mouse/human) monoclonal antibody, an epidermal growth factor receptor (EGFR) inhibitor. Many large clinical trials demonstrated that for RAS wild-type metastatic colorectal cancer (mCRC), especially left-sided RAS wild-type mCRC, cetuximab can prolong OS. But some of patients have primary resistance to cetuximab and for all patients received cetuximab will develop secondary resistance. Cell-free or circulating tumour DNA (ctDNA) including primary site and metastatic site genetic information, which can avoid tumor heterogeneity. The results of paired test detection of tissue and ctDNA showed there is 93% consistency in RAS testing. Therefore, dynamic monitoring ctDNA during anti-EGFR targeted treatment of RAS wild-type mCRC patients can implement prognosis of efficacy and response evaluation in real-time. Besides, it can monitor the variation features of resistance gene and find resistance gene in real-time. According the situation of gene change to find potential drug resistance mechanism and formulate individualization treatment plan.
