27 Background: Minimal residual disease, defined by ctDNA+ in the absence of macroscopic of disease, represents a new and clinically poorly defined subset of patients (pts). While observational cohorts have been reported on the prognosis of MRD, there is little information on the impact of returning and acting on ctDNA results on the subsequent ability to detect radiographic disease. Here we provide real-world evidence form a large prospective cohort where ctDNA testing was routinely performed and returned to pts and providers, providing opportunities to understand the prognostic performance of ctDNA in practice, including the rate of false negatives defined as radiographic recurrence without detectable ctDNA. Methods: The INTERCEPT program enrolled pts undergoing curative intent surgery for stages II-IV CRC at MD Anderson Cancer Center. A tumor-informed MRD assay (Signatera) was drawn post-operatively and every 3 months as per established reimbursement guidelines. Pts enrolled between Jan-Dec 2022 were included with follow up through Aug, 2023. Post-op timepoint was defined as any test within 6.5 months of surgery to include adjuvant therapy. A false negative result was defined as a negative test but with radiographic detection of recurrence within the subsequent 4 months. Results: A total of 1,140 pts were included, with 44.7% female and 39% with advanced disease. At least one ctDNA+ result was obtained in 338 patients (29.6%). When limited to pts with a post-operative/post-adjuvant timepoint (n= 520) and a median follow up of 10.4m, the 12m DFS was 94.2% for ctDNA-, and 54.3% for pts with at least 1 ctDNA+ test (median DFS of 14.9m); HR 17.67 (95% CI: 10.08 – 30.99), p<0.0001. When segregated by stage, ctDNA remained the most important predictor of outcomes [Table], such that pts with stage IV ctDNA- had better prognosis than pts with stage II ctDNA+ (38.9% vs 87.7% 12mDFS, p=.002). For 15 pts, we detected a false negative ctDNA, representing a rate of 1.3% (15/1140) corresponding to a negative predictive value (NPV) of 98.1%. Conclusions: In this first prospective real-world ctDNA program, MRD testing had a high NPV (98.1%) with very few false negative cases. The prognostic importance of ctDNA was confirmed and exceeded the risk prediction of stage alone, underlying and supporting the importance of introducing the test in practice and the need to investigate interventional studies, as are ongoing in the INTERCEPT program (crcmrd.org). [Table: see text]
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