Aushev, Vasily N.

3516 Background: ICIs produce durable benefit in MSI-H CRC, yet optimal treatment duration and monitoring strategies remain unclear. ctDNA enables minimally invasive assessment of molecular response during and after ICI. We evaluated real-world treatment patterns, outcomes, and longitudinal ctDNA dynamics in pts with MSI-H CRC treated with ICI. Methods: Pts with MSI-H mCRC treated with first-line ICI were identified from Natera’s Real-World Database with linked longitudinal ctDNA results (Signatera, Natera, Inc.) and commercial claims data (Forian’s Hybrid data ecosystem, CHRONOS). Overall survival (OS) was estimated using available mortality data (Veritas Data Research, Fact of Death Mortality Data Index). ctDNA status was assessed pre-ICI when available and longitudinally following ICI initiation. Outcomes included OS and time to next trmt (TTNT); ctDNA dynamics following ICI discontinuation were descriptively evaluated. Results: Among 559 pts treated with first line ICI (pembrolizumab [70.1%], ipilimumab+nivolumab [15.7%], and nivolumab [11.8%]), the median duration of ICI was 266 days. Baseline (pre-ICI) ctDNA results were available for 180 pts, including 38% who were treated with chemotherapy, and most pts (71.7%, 129/180) were ctDNA-positive (ctDNA(+)) prior to ICI initiation. Of these, 89.9% (116/129) had ctDNA-timepoints after the start of ICI, and 81.0% (94/116) achieved anytime ctDNA clearance (from ctDNA(+) to negative), while 19.0% (22/116) remained ctDNA(+). ctDNA(+) at anytime after the start of ICI (HR: 8.0, p < 0.0001) or on first result after the start of ICI (HR: 3.4, p < 0.0001) was associated with inferior OS compared ctDNA-negativity (ctDNA(-)) at these time points. Among pts whose first post-ICI test was ctDNA(+), 32% switched treatments, with a median TTNT of 302 days, compared to only 6.6% of pts (median TTNT 683 days) whose first post-ICI test was ctDNA(-). First post-ICI ctDNA status was associated with longer ICI duration (median 192 days for ctDNA(+) vs 303 days for ctDNA(-)), and ctDNA(+) was predictive of inferior OS (HR: 4.9; p < 0.001). ctDNA after the end of ICI was available for 392 patients; it was persistently negative in 77.2% (303/392), persistently positive in 12.8% (50/392), cleared after the end of ICI (positive to persistently negative) in 4.1%, and the remaining 5.9% had variable patterns (e.g. positive to negative to positive). Conclusions: In this large real-world cohort of MSI-H mCRC treated with ICI, longitudinal ctDNA dynamics strongly correlated with treatment durability, time to subsequent therapy, and OS. These findings support further evaluation of ctDNA to inform treatment duration and surveillance strategies in MSI-H mCRC.

Objective: In this study, we evaluate the utility of ctDNA analysis in a large cohort of patients for whom ctDNA testing was ordered commercially with real-world application. Summary Background Data: Circulating tumor DNA (ctDNA) has emerged as a prognostic and predictive biomarker for assessing post-surgical molecular residual disease (MRD) and response to treatment. Methods: A real-world data analysis was performed using commercial ctDNA testing (SignateraTM) from patients (N=795, n=5,971 plasma samples) with stage I-III colon cancer treated at multiple US institutions. The association of ctDNA detection within the MRD window, during surveillance, and the impact of ACT was correlated with patient outcomes. Results: ctDNA-positive patients during the MRD window and surveillance showed significantly shorter DFS compared to ctDNA-negative patients (hazard ratio (HR): 9.85, P<0.0001; HR: 26.91, P<0.0001). Multivariate analysis of the MRD window revealed ctDNA-positivity as the most significant factor associated with inferior DFS (adjHR: 7.7, P<0.001). MRD-positive patients who received ACT showed improved DFS compared to patients observed post-surgery (adjHR: 6.1, FDR adj P=0.0007). No ACT benefit was observed in MRD-negative patients (adj HR: 1.20, FDR adj P=0.768). On evaluating ctDNA dynamics from MRD to surveillance, patients who remained ctDNA-positive or converted from negative to positive showed a significantly inferior DFS (HR: 34.40, P<0.0001; HR: 13.65, P<0.0001) compared to persistently ctDNA-negative patients. Conclusions: Postsurgical ctDNA detection is prognostic of relapse and potentially predictive of ACT benefit in patients with resectable colon cancer, which may enable personalized surveillance, intervention, and/or trial options, ultimately improving patient outcomes.

Abstract Background: Tumor-informed circulating tumor (ct) DNA testing is recognized as a powerful predictor of CRC recurrence. However, the benefit of systemic therapy to prevent or delay clinical recurrence in patients (pts) with molecular recurrence after curative surgery remains uncertain. Methods: Pts with CRC who had undergone curative resection of primary and/or metastatic sites + standard of care (SoC) adjuvant treatment, if applicable, were enrolled in ALTAIR study if they (1) prospectively tested positive for ctDNA using a clinically validated, personalized assay (Signatera™, Natera, Inc.) within 3 months before enrollment and (2) had no recurrence on radiological (CT) imaging. Pts were randomized to receive FTD/TPI or placebo for 6 months. CT scans and ctDNA analyses were conducted every 2 months in the first year, every 3 months in the second year, and every 6 months in the third year. The primary endpoint was disease-free survival (DFS), with secondary endpoints including ctDNA clearance, overall survival (OS), and adverse events. The study assumed a median DFS of 8 months in the placebo group, an HR of 0.667 for the FTD/TPI group, 0.05 significance level, 0.80 power, 2-year enrollment, and 1-year follow-up, requiring 240 pts and 190 DFS events. Baseline ctDNA levels were evaluated by mean tumor molecules (MTM)/ml. Results: Between July 2020 and June 2023, 243 pts were enrolled and randomized to FTD/TPI (n=122) or placebo (n=121). Baseline characteristics were balanced, and 96.3% of pts received SoC treatment postoperatively. FTD/TPI group had a median DFS of 9.30 months vs. 5.55 months in the placebo group, which did not reach statistical significance in the primary population (HR, 0.79; 95% CI, 0.60-1.05; P = 0.107). The benefit was highly pronounced, however, in stage IV pts (HR: 0.53, P = 0.012). In addition, after excluding pts with low ctDNA levels (&lt;0.179 MTM/mL, threshold determined by ROC analysis) from both arms, significant benefit with FTD/TPI was observed in the primary population, resulting in an improved DFS (N=154, HR: 0.61 95% CI: 0.43-0.85; P = 0.003) with a median DFS of 8.12 months for FTD/TPI vs. 3.89 months for placebo; consistent with these findings, a trend toward higher ctDNA clearance rate was observed for the FTD/TPI group (8.33%), compared to placebo (4.05%).OS data remain immature, with 24 events reported across both arms. Grade ≥3 adverse events occurred in 73.0% of the FTD/TPI arm versus 3.3% in the placebo arm, with no new safety signals. Conclusions: Although statistical significance was not reached in the primary population, FTD/TPI showed benefit in pts with high molecular tumor burden and/ or Stage IV disease, resulting in improved DFS. Citation Format: Hideaki Bando, Jun Watanabe, Masahito Kotaka, Nobuhisa Matsuhashi, Eiji Oki, Yoshito Komatsu, Manabu Shiozawa, Keiji Hirata, Yuji Miyamoto, Kun-Huei Yeh, Shruti Sharma, Vasily Aushev, Adham Jurdi, Minetta C. Liu, Alexey Aleshin, Ichiro Takemasa, Daisuke Kotani, Akihito Sato, Toshihiro Misumi, Yoshiaki Nakamura, Qian Shi, Hiroya Taniguchi, Takeshi Kato, Takayuki Yoshino. A randomized, double-blind, phase III study comparing trifluridine/tipiracil (FTD/TPI) versus placebo in patients with molecular residual disease following curative resection of colorectal cancer (CRC): The ALTAIR Study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT131.