QS206 - The Clinical Utility of Blood-Based Multi-Locus Circulating Tumor DNA Methylation Assay for Colorectal Cancer Diagnosis : Interim result, Case-control study

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Purpose/Background: Liquid biopsy methods, particularly circulating tumor DNA (ctDNA) methylation profiling, have emerged as potential alternatives. This ongoing prospective case-control study aims to assess the diagnostic efficacy of ctDNA methylation profiling as a non-invasive tool for CRC detection by using ColonCatch® platform, which targets six ctDNA methylation markers.

Methods/Interventions: We are targeting an enrollment of 254 participants aged 50-79, including 120 colorectal cancer patients who had not undergone neoadjuvant treatment or endoscopic resection, and 134 healthy controls. This interim analysis evaluated data from 35 colorectal cancer patients and 57 controls after excluding 22 samples that failed to pass qualification criteria. Plasma samples from cancer patients were collected preoperatively on the day of surgery, while control samples were obtained during outpatient visits. ColonCatch® test-positivity was defined as detecting at least one of six methylation markers (Septin9, IKZF1, BCAT1, Septin9-2, BCAN, and VAV3). Baseline characteristics such as sex, age, CEA levels, and smoking status were compared between CRC and control groups. For CRC patients, further analysis examined associations between marker positivity and clinical outcomes, including tumor size, pathological stage, and lymphovascular invasion.

Results/Outcomes: Among the samples analyzed, 33 participants (35.9%) tested positive for ctDNA methylation. The overall cohort consisted of 62% males, with an average age of 61.0 ± 7.4 years. ColonCatch® positivity demonstrated a statistically significant difference between the CRC and control groups (p < 0.001). The platform showed a sensitivity of 74% and specificity of 88% for diagnosing colorectal cancer, while CEA exhibited a lower sensitivity of 26% but a high specificity of 98%. In CRC patients, those who tested positive for ctDNA methylation markers had larger tumors (5.7 ± 2.0 cm vs. 2.2 ± 1.3 cm, p < 0.001) and more advanced pathological stages (p = 0.007). When T staging and N staging were analyzed separately, significant differences were observed (p = 0.005 and p = 0.041, respectively). Among the six methylation markers tested, BCAT1 had the highest positivity rate, with 16 positive samples, followed by Septin9 with 14 positive samples. The median number of positive methylation markers in cancer patients was 2.0 [0.5; 2.5]. As the cancer stage increased, the proportion of patients testing positive for more than two methylation markers significantly rose—from 9.1% in stage I to 66.7% in stage IV (p = 0.026), with stage IV patients having a median of 4.0 [3.0; 5.0] markers positive. For the nine false-negative CRC patients, seven were in pathological stage I.

Conclusion/Discussion: This study suggests that ctDNA methylation profiling could serve as a non-invasive and specific screening tool for colorectal cancer. Additionally, the use of multi-locus methylation markers shows potential for predicting tumor staging, though further research is needed to confirm these findings. Ongoing analysis will provide more definitive insights into the clinical utility of this approach.