Tumor markers, carcinoembryonic antigen (CEA), carbohydrate antigen 19‐9 (CA19‐9), lactate dehydrogenase (LDH), were significantly associated with ctDNA level of patients with mCRC (P = 0.000007, P = 0.006 and P = 0.00001, respectively, Table 2), and maximum and sum of the tumor diameter were also significantly associated with their ctDNA level (P = 0.00002 and P = 0.00009, Table 2). This evidence concerns the gene CEACAM5 and neoplasm.