Serum <scp>DNA</scp> methylome of the colorectal cancer serrated pathway enables non‐invasive detection

The clinical relevance of the colorectal cancer serrated pathway is evident, but the screening of serrated lesions remains challenging. We aimed to characterize the serum methylome of the serrated pathway and to evaluate circulating cell‐free DNA (cfDNA) methylomes as a potential source of biomarkers for the non‐invasive detection of serrated lesions. We collected serum samples from individuals with serrated adenocarcinoma (SAC), traditional serrated adenomas, sessile serrated lesions, hyperplastic polyps and individuals with no colorectal findings. First, we quantified cfDNA methylation with the MethylationEPIC array. Then, we compared the methylation profiles with tissue and serum datasets. Finally, we evaluated the utility of serum cfDNA methylation biomarkers. We identified a differential methylation profile able to distinguish high‐risk serrated lesions from no serrated neoplasia, showing concordance with tissue methylation from SAC and sessile serrated lesions. Serum methylation profiles are pathway‐specific, clearly separating serrated lesions from conventional adenomas. The combination of ninjurin 2 ( NINJ2 ) and glutamate‐rich 1 ( ERICH1 ) methylation discriminated high‐risk serrated lesions and SAC with 91.4% sensitivity (64.4% specificity), while zinc finger protein 718 ( ZNF718 ) methylation reported 100% sensitivity for the detection of SAC (96% specificity). This is the first study exploring the serum methylome of serrated lesions. Differential methylation of cfDNA can be used for the non‐invasive detection of colorectal serrated lesions.