381P A tumor-informed, hybrid-capture based ctDNA assay for minimal residual disease (MRD) detection in colorectal cancer (CRC) patients after curative surgery

Background MRD detection using ctDNA analysis after curative treatment may help identify patients at higher risk of relapse and improve treatment outcomes by enabling personalized treatment.We have analyzed the clinical performance of a recently developed tissue-informed, hybrid-capture NGS-based ctDNA MRD assay in CRC. Methods Patients with stage II-III CRC treated with standard care surgery and/or adjuvant therapy with archived surgical tissue and preoperative and postoperative 3-week plasma samples were selected fr|om a multi-center, prospective CRC cohort.For ctDNA MRD assay, AlphaLiquid Detect (IMBdx, Seoul, Korea) was used. It builds a personalized ctDNA panel for each patient including most of the variants meeting prespecified criteria found in tissue whole exome-sequencing data sequenced at ∼200-300x. Variants with clinical importance and high allele frequency are prioritized over potential germline variant sites and low mappability regions. A hybrid-capture based NGS data is generated for cell-free DNA at >100,000x to find ctDNA at a limit of detection <0.005%. Results A total of 71 patients (stage II/III 27(38.0%)/44(62.0%)) were successfully analyzed. 55 (77.5%) patients were treated with adjuvant therapy after surgery, and 3-year recurrence-free survival rate (RFS) was 67.5%. Personalized panels based on WES results included a median of 61 (6-166) mutations per patient. Using a cutoff value of 2 or more mutations for MRD positivity, 61/70 (87.1%) and 13/71 (18.3%) patients were confirmed to have ctDNA mutations exceeding the threshold fr|om their preoperative and postoperative plasma samples, respectively. The postoperative MRD positivity was strongly associated with poor RFS (HR = 8.23, 95% CI 3.3 – 21, p < 0.001). A simulation study sub-selecting fewer variants in the pre-designed panels showed a substantial decrease in the sensitivity but minimal changes in specificity, demonstrating the strength of the assay targeting entire variants fr|om each patient. Conclusions MRD positivity as determined by the tumor-informed, hybrid-capture based ctDNA assay showed a strong association with poor RFS in CRC.