Therefore, as our first attempt in liquid biopsy of CRC, we tested plasma (300 μl) of stage IV CRC patients (carcinoma N = 20 and normal N = 20) using the cell-free circulating methylated DNA (cMethDNA) assay with the 8-gene subset TMEFF2, COL6A2, ZNF671, ARHGEF7, TM6SF1, MAL, GPX7, and AKR1B1. TM6SF1, ZNF671, and COL6A2 were included in this liquid biopsy panel despite the high background observed in normal colon tissue (Table 2 and Additional file 1: Fig. S1). Here, GPX7 is linked to carcinoma.