Correlation of presurgical circulating tumor DNA (ctDNA) levels with pathologic (p) stage and lymph node (LN) burden in localized colon cancer.

3048 Background: Accurate preoperative staging is vital for tailoring neoadjuvant therapy (NAT) in localized colon cancer. However, clinical staging often diverges from pathological findings due to limitations of imaging modalities in assessing pathologic LN (pLN) involvement and inter-observer variability. This study evaluated the association between presurgical ctDNA levels, microsatellite instability (MSI) status, and pLN burden across pStages I–III in colon cancer. Methods: This retrospective study included patients (pts) with pStage I-III colon cancer from the GALAXY study with available presurgical ctDNA levels (mean tumor molecules/mL; MTM/mL) assessed by a personalized tumor-informed assay (Signatera, Natera, Inc). Key exclusions included receipt of NAT, inconsistent pLN classification, pN1c disease, and missing MSI status. Conditional inference tree modeling was used to hierarchically evaluate clinicopathologic and molecular risk factors for their association with presurgical ctDNA levels. Results: Of the 3,473 pts (14.4%, 43.1% and 42.5% with pStage I, II and III, respectively) included, 90.2% had microsatellite stable (MSS) tumors. The conditional inference tree partitioned the cohort into five subgroups of distinct presurgical ctDNA level distributions defined by pStage, pLN burden, and MSI status, and demonstrated the pStage to be the strongest determinant of presurgical ctDNA levels. pStage I pts had uniformly low MTM/mL. In contrast, pStage II–III pts had higher and more variable MTM/mL levels, which were stratified by pLN burden and further differentiated by MSI status within each nodal category. Presurgical ctDNA levels were significantly higher in pLN-positive vs pLN-negative pts (median 2.52 vs 1.23 MTM/mL, p <0.0001) and in pStage IIB-III vs pStage I-IIA pts (median 2.64 vs 1 MTM/mL, p <0.0001). While presurgical ctDNA levels did not differ significantly based on MSI status alone, within both MSS and MSI-H subgroups, they were significantly higher in pLN-positive pts vs pLN-negative pts (MSI-H: median 4.40 vs 1.19 MTM/mL; MSS: median 2.41 vs 1.25 MTM/mL). Similar results were observed when grouped based on pStage I/II vs III. Specifically among pLN-positive pts, presurgical ctDNA levels increased with higher pLN burden (MSI-H: median 15.13 vs 3.75 MTM/mL for ≥4 vs 1-3 LN, p=0.049; MSS: median 3.70 vs 1.96 MTM/mL for ≥4 vs 1-3 LN, p<0.0001). Conclusions: Presurgical ctDNA levels reflect a hierarchical interplay of pathologic stage, lymph node burden, and MSI status rather than any single clinicopathologic factor. High presurgical ctDNA levels reliably correlated with pStage and pLN positivity in localized colon cancer, supporting the development of models incorporating presurgical ctDNA quantification to better select pts for NAT and their evaluation in prospective trials. Clinical trial information: 000039205.