Translational Validation of a Novel Multi-Locus ctDNA Methylation Assay for Early Detection and Stratification of Colorectal Cancer: An Exploratory Prospective, Case-Control Study

To evaluate the diagnostic performance and clinicopathologic relevance of a multi-locus circulating tumor DNA methylation assay. In this prospective, single-center, case-control exploratory study, we enrolled 35 patients with colorectal cancer undergoing surgery and 57 healthy controls undergoing screening colonoscopy at the Asan Medical Center, Seoul, Republic of Korea between July 2024 and January 2025. Peripheral blood was collected before surgery or colonoscopy, and circulating tumor DNA methylation was analyzed using a multi-locus panel targeting Septin9, IKZF1, BCAT1, Septin9-2, BCAN, and VAV3. The main outcomes were test accuracy (sensitivity, specificity, and area under the curve [AUC]) and associations between methylation marker positivity and clinicopathologic features. Circulating tumor DNA was positive in 74.3% of the patients and 12.3% of controls, yielding a sensitivity of 74.3%, specificity of 87.7%, and an AUC of 0.837, whereas serum carcinoembryonic antigen exhibited lower sensitivity (25.7%). Sensitivity in stage I disease was limited (36.4%). Circulating tumor DNA-positive tumors were larger (5.7 cm vs. 2.2 cm, p < 0.001) and had more advanced T and N stages. The number of positive markers increased with pathologic stage (p = 0.003). Individual marker analysis revealed that BCAT1, Septin9-2, and VAV3 were associated with higher T stage, whereas BCAN positivity was linked to nodal metastasis. The six-marker circulating tumor DNA methylation assay demonstrated acceptable diagnostic accuracy, with multi-locus patterns associated with tumor burden and invasive features. However, sensitivity for early-stage disease was limited. The assay may serve as a complementary tool for screening and risk stratification.