Aleshin, Alexey

11177 Background: Early detection of recurrence after curative-intent treatment is a critical priority, traditional imaging often detects relapse when disease burden is high, potentially limiting treatment efficacy. ctDNA has emerged as an established prognostic biomarker for molecular residual disease (MRD) detection and early relapse. We performed a real-world meta-analysis on published datasets that utilized personalized, tumor-informed ctDNA testing to assess its performance across tumor types and clinical management approaches. Methods: Real-world studies published from December 2022 to December 2025 using the personalized, tumor-informed Signatera ctDNA assay (Natera, Inc.) were included. Eligibility required ctDNA assessment in the MRD (2–16 weeks post-surgery (histology dependent)/pre adjuvant therapy (ACT)) and/or surveillance (post-ACT/end of the MRD window if no ACT was given) settings, with outcomes stratified by ctDNA status and hazard ratios (HR) reported from univariable or time-dependent Cox regression analysis. Exclusions included: clinical trials, biobanks, metastatic disease treated with palliative intent, case reports, reviews, editorials, or commentaries. Clinical outcomes were harmonized into a composite event-free survival (EFS) endpoint (time to recurrence, progression, or death). Pooled HRs and 95% CIs were estimated using random and fixed effects models and heterogeneity between studies was assessed using the I 2 and Cochran’s Q test. Median lead time from ctDNA-positivity to radiographic or clinical recurrence was summarized when available. Results: We identified 18 eligible publications comprising 3,004 unique patients across 15 solid tumor types. During the MRD window, ctDNA positivity was associated with a significantly increased risk of an EFS event compared with ctDNA negativity (pooled HR: 8.15; 95% CI: 6.12–10.85, I 2 = 0.00%, P = 0.844, n = 13). During the surveillance window, inclusive of post-definitive treatment, ctDNA positivity conferred an even greater EFS risk (pooled HR: 18.30; 95% CI: 14.17–23.65, I 2 = 0%, P = 0.911 for heterogeneity, n = 16). Across studies, ctDNA detection during surveillance preceded radiographic or clinical recurrence by a median of 3.20 months (95% CI: 2.50-4.10, P < 0.0001, n = 10), although this varied substantially by study/tumor type (I 2 = 80.9%). Conclusions: In this pan-cancer real-world meta-analysis, ctDNA positivity assessed using a tumor-informed assay was highly prognostic following curative-intent therapy at all timepoints evaluated with low heterogeneity between studies. These findings support the broad clinical utility of tumor-informed ctDNA testing for post-treatment risk stratification and longitudinal disease monitoring across solid tumors.

Importance Observational studies have associated use of aspirin and selective cyclooxygenase inhibitors with decreased recurrence and improved survival in patients with colon cancer. While randomized clinical trials have not shown benefit across all patients, these findings suggest that select subgroups may benefit from their use. Despite the well-established prognostic value of circulating tumor DNA (ctDNA), its role in guiding treatment remains unclear. Objective To investigate the predictive value of postoperative ctDNA for survival outcomes with adjuvant celecoxib alongside conventional chemotherapy in patients with stage III colon cancer. Design, Setting, and Participants This was a post hoc analysis of the phase 3 Cancer and Leukemia Group B (now Alliance)/Southwest Oncology Group 80702 randomized clinical trial (2010-2015) assessing adjuvant celecoxib vs placebo and 3 vs 6 months of adjuvant 5-fluorouracil, leucovorin, and oxaliplatin for stage III colon cancer. Patients consented to biospecimen collection and had ctDNA analysis performed. Data analysis was performed from September 2024 to June 2025. Exposures Postoperative ctDNA positivity was determined using a clinically validated, tumor-informed 16-plex-polymerase chain reaction-next-generation sequencing assay (Signatera; Natera Inc) performed between surgery and initiation of adjuvant therapy. Main Outcomes and Measures Disease-free survival (DFS) and overall survival (OS). Survival by ctDNA status and adjuvant celecoxib use were assessed as part of a post hoc companion study with prespecified statistical analysis plan. Results Among 940 patients (mean [SD] age, 60.9 [10.8] years; 426 female [45.3%] and 515 male [54.7%] individuals; 222 [23.6%] with prior low-dose aspirin use; and median follow-up of 6.0 [95% CI, 6.0-6.0] years), 767 (81.6%) were ctDNA negative and 173 (18.4%) were ctDNA positive. ctDNA positivity was highly prognostic of worse DFS (reference, ctDNA negativity; adjusted hazard ratio [aHR], 6.12; 95% CI, 4.66-8.03) and OS (aHR, 5.86; 95% CI, 4.19-8.19). In patients with ctDNA positivity, celecoxib was associated with improved DFS (aHR, 0.61; 95% CI, 0.42-0.89) and OS (aHR, 0.62; 95% CI, 0.40-0.96) compared to placebo. Among patients with ctDNA negativity, celecoxib did not provide survival benefit (DFS: aHR, 0.76; 95% CI, 0.53-1.09; OS: aHR, 0.85; 95% CI, 0.54-1.36), although the interaction was not significant ( P for interaction, .41 and .33 for DFS and OS, respectively). These findings persisted when stratifying patients by microsatellite instability status and PIK3CA mutational status. Conclusion and Relevance The findings of this post hoc analysis suggest that ctDNA status has the potential to inform clinical decision-making among patients with stage III colon cancer who should consider adjuvant celecoxib in addition to conventional chemotherapy. Trial Registration ClinicalTrials.gov Identifier: NCT01150045

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.

LBA22 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 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, but this difference did not reach statistical significance in the primary population (HR, 0.79; 95% CI, 0.60-1.05; P = 0.107). The FTD/TPI benefit was highly significant in resected oligometastatic stage IV pts as shown in Table. The baseline MTM/ml levels were significantly higher in resected oligometastatic Stage IV pts vs non-Stage IV (0.68 vs 0.32, P = 0.024). Overall, FTD/TPI benefit was significantly pronounced with higher MTM/mL, with linear benefit observed with increasing MTM/mL values at the enrollment time point. 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 clinically meaningful DFS benefit in pts with resected oligometastatic disease and a trend towards increasing DFS benefits with increasing MTM/mL values. Clinical trial information: NCT04457297 . Number Baseline MTM/ml Median DFS FTD/TPI(months) Placebo (months) Primary population 243 0.40 9.30 5.55 HR, 0.79 P = 0.107 Stage IV 66 0.68 9.76 3.96 HR, 0.53 P = 0.012 Non-Stage IV 177 0.32 9.26 6.05 HR, 0.86 P = 0.378

LBA14 Background: CALGB/SWOG 80702 previously showed that the addition of celecoxib to standard adjuvant chemotherapy with FOLFOX did not significantly improve disease-free survival (DFS) in patients with stage III colon cancer. Here, we evaluated the prognostic and predictive value of ctDNA in identifying a subpopulation of patients who may benefit from celecoxib. Methods: In the subset of patients with adequate biospecimens who participated in CALGB/SWOG 80702, a randomized phase III trial of 3 versus 6 months of adjuvant 5-FU, leucovorin, oxaliplatin (FOLFOX) +/- celecoxib, ctDNA assessment was performed using a clinically validated, tumor-informed 16-plex mPCR-NGS assay (Signatera(TM), Natera, Inc.) after surgery and before the start of adjuvant therapy (baseline). The Kaplan-Meier method was used to describe the distribution of survival time based on ctDNA positivity and log-rank testing was performed. Cox proportional hazards models were used to examine unadjusted associations between ctDNA positivity and disease-free (DFS) and overall survival (OS). Two-sided P values equal to or less than 0.05 were considered statistically significant, except for interaction P values (tested with a likelihood ratio). Results: In total, 1,011 of the 2,526 patients who participated in 80702 had ctDNA testing results from baseline; 189 were ctDNA positive (18.7%). ctDNA positivity associated with male sex, higher T stage, and N2 (versus N1) stage. ctDNA positivity was significantly associated with worse DFS (hazard ratio [HR] 6.52 [95% confident interval (CI) 5.09-8.34; p<0.0001] and OS (HR 6.28 [95% CI 4.63-8.51; p<0.0001]). Three-year DFS was 86.6% in ctDNA-negative cases and 36.8% in ctDNA-positive cases. Among patients who were ctDNA negative, celecoxib use was not significantly associated with worse DFS as compared to placebo (HR 0.75 [95% CI 0.54-1.05; p=0.095]) with a three-year DFS of 87.7% versus 85.5%, respectively. Among ctDNA-positive patients, celecoxib significantly improved DFS compared to placebo (HR 0.59 [95% CI 0.42-0.85; p=0.004]) with a three-year DFS of 44.1% versus 26.6% (P interaction = 0.25). Similar results were seen for overall survival with a hazard ratio of 0.86 (95% CI 0.56-1.33; p=0.49) for ctDNA negative cases and 0.63 (95% CI 0.41-0.96; p=0.028) for ctDNA-positive cases for celecoxib versus placebo (P interaction = 0.28). Conclusion: In a randomized phase III adjuvant therapy trial for stage III colon cancer, ctDNA was highly prognostic of DFS and OS. ctDNA positivity also appeared predictive of the benefit of adjuvant celecoxib for DFS and OS. These results suggest a potential role for ctDNA in determining which patients should consider celecoxib in addition to standard FOLFOX adjuvant therapy. Clinical trial information: NCT01150045 .

Abstract Background: We compared the predictive and prognostic value of ctDNA dynamics in high-risk hormone receptor-positive/HER2-negative (HR+/HER2-) and triple negative breast cancer (TNBC) receiving neoadjuvant chemotherapy (NAC) enrolled in the I-SPY 2 trial (NCT01042379). To our knowledge, this is the largest ctDNA study in breast cancer in the neoadjuvant setting. Methods: Blood samples were collected at pre-treatment (T0), during treatment (T1 at 3 weeks, and T2 at 12 weeks) and after NAC (T3 at 24 weeks) from 106 HR+/HER2- and 97 TNBC patients. Plasma samples (n=734) were analyzed using a personalized and tumor-informed mPCR NGS-based ctDNA test (SignateraTM). Patients, all high risk for recurrence by MammaPrint, received paclitaxel-based treatment +/- experimental therapy followed by anthracycline. The median follow-up was 3.0 years (0.5 to 6.5). The predictive and prognostic value of ctDNA dynamics and status at different timepoints were examined. Our analysis is exploratory and does not adjust for other biomarkers. Results: Pretreatment ctDNA positivity (Fisher p&lt;0.0001) and levels (mean tumor molecules/mL, MTM/mL, t test p=0.0062) were significantly higher in TNBC (90.7%, 14.7 MTM/mL) than in high risk HR+/HER2- (66.0%, 5.5 MTM/mL). Early and late ctDNA clearance during treatment (3 and 12 weeks of NAC) was predictive of pathologic complete response (pCR) and residual cancer burden (RCB), class 0-III, in TNBC but not HR+/HER2- (Table). In both subtypes: (1) ctDNA was a significant negative prognostic factor for distant recurrence-free survival (DRFS) at all timepoints (p&lt;0.05) except at pretreatment; (2) all patients who achieved pCR were ctDNA-negative after NAC; (3) among non-responding patients, ctDNA-negativity after NAC was associated with improved DRFS (Table). Conclusions: The predictive value of ctDNA for prediction of pCR and RCB differed between subtypes (HR+/HER2- vs. TNBC), while similar prognostic value was observed. In TNBC, early clearance of ctDNA at 3 weeks was a significant predictor of favorable response to NAC. Compared to patients who were ctDNA-positive after NAC, ctDNA-negative status in both subtypes was associated with improved DRFS even in patients with residual cancer (no pCR or RCB-II/III). These findings could inform on the design of future studies that seek to demonstrate the utility of ctDNA in the curative setting. Predictive and prognostic significance of ctDNA in early breast cancer in the neoadjuvant setting HR+HER2- (n=106) TNBC (n=97) Predictive value for prediction of pCR and RCB Fisher p-value Fisher p-value Early ctDNA clearance (between T0 and T1) and pCR 0.4521 &lt;0.0001 Late ctDNA clearance (between T0 and T2) and pCR 0.8071 0.0004 Early ctDNA clearance (between T0 and T1) and RCB (0-III) 0.1360 &lt;0.0001 Late ctDNA clearance (between T0 and T2) and RCB (0-III) 0.4869 0.0004 Early ctDNA clearance at T1 and pCR rates pCR rate pCR rate ctDNA clearance (ctDNA+ at T0/ctDNA- at T1) 21% 67% Late ctDNA clearance (betweeNo early clearance (ctDNA+ at T0/ctDNA+ at T1) 13% 14% Prognostic value for prediction of DRFS Log rank p-value Log rank p-value ctDNA at T3 and pCR vs no PCR 0.0002 &lt;0.0001 ctDNA at T3 and RCB (0-I vs II-III) 0.0110 &lt;0.0001 Timepoints: T0 - pretreatment; T1 - three weeks after treatment initiation; T2 - at 12 weeks, between paclitaxel-based and anthracycline regimens; T3- after neoadjuvant chemotherapy prior to surgery Citation Format: Mark Jesus Mendoza Magbanua, Lamorna Brown Swigart, Derrick Renner, Svetlana Shchegrova, Gillian L. Hirst, Christina Yau, Denise M. Wolf, Hsin-Ta Wu, Ekaterina Kalashnikova, Amy L. Delson, A. Jo Chien, Debu Tripathy, Smita Asare, Raheleh Salari, Angel Rodriguez, Bernhard Zimmermann, Himanshu Sethi, Alexey Aleshin, Paul Billings, Rita Nanda, Hope S. Rugo, Laura J. Esserman, Minetta C. Liu, Angela DeMichele, Laura van 't Veer. Comparison of the predictive and prognostic significance of circulating tumor DNA in patients with high risk HER2-negative breast cancer receiving neoadjuvant chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB111.

Abstract Background: In the I-SPY 2 TRIAL, the addition of P to standard NAC resulted in more than doubling of the pathologic complete response (pCR) rates for both hormone receptor-positive (HR+)/HER2- and triple-negative (TN) early breast cancer (EBC) patients (pts) compared to NAC only (Nanda et al, JAMA Oncol, 2020). At 3 years, distant recurrence-free survival (DRFS) rates in pts with pCR following NAC+P was &gt;95%. We hypothesized that ctDNA can serve as a predictive biomarker of response and survival in pts treated with NAC. Methods: A personalized ctDNA test (Signatera) was performed on 511 serial plasma samples from 138 pts with high-risk HR+/HER2- (n=77) or TN (n=61) stage II/III EBC. Pts received P with paclitaxel (Tx) followed by AC (P arm, n=42) or standard NAC only (n=96), an exploratory subset of pts evaluated for P efficacy. Plasma was collected; pretreatment (T0), 3 weeks after treatment initiation (T1), between Tx+/-P and AC regimens (T2), and prior to surgery (T3). ctDNA was deemed positive with a minimum of 2 of the pt specific tumor mutation fragments detected in cfDNA. Association of ctDNA with response and survival was analyzed using logistic and Cox regressions with pCR and DRFS as endpoints. Median follow-up was 2.8 years. Results: Detection of ctDNA decreased over time (P arm: T0-81%, T1-50%, T2-19%, T3-3%) and NAC only: T0-82%, T1-65%, T2-26%, T3-10%). ctDNA data at T0 and T1 was available for 96% (132/138) of pts in P arm or NAC only (Table). Among ctDNA+ patients at baseline, clearance at T1 was significantly associated with pCR (OR=1.92, ctDNA+/-; OR=0.27, ctDNA+/+; LR p&lt;0.001). This association remained significant after adjustment for HR status and treatment (LR p&lt;0.001) and P arm or NAC only (P: LR p=0.03; NAC: LR p=0.01). ctDNA data at T0, T1, and T2 was available for 86% (118/138) pts. (Table). Among all ctDNA+ pts at baseline, dynamics through T2 was associated with pCR (OR=1.44, ctDNA+/-/-; OR=0.33, ctDNA+/+/-, OR=0.12, ctDNA+/+/+; LR p=0.0011). This association remained significant when adjusted for HR status and treatment (LR p&lt;0.001). Analysis within individual treatments showed significant association for NAC (LR p=0.040) and a non-significant trend in NAC+P (LR p=0.063), likely due to smaller sample size. All pts who achieved pCR were ctDNA- at T3 (n=34). Among those who failed to achieve pCR (n=81), DRFS was significantly better in ctDNA- (n=72/81; 20 in P and 52 in NAC) versus ctDNA+ pts (n=9/81; 1 in P and 8 in NAC) (adjusted HR 0.13; 95% CI 0.05-0.37). Conclusions: These exploratory results align with our previous findings that early clearance of ctDNA during NAC treatment was significantly associated with increased likelihood of achieving pCR. Additionally, we show that ctDNA clearance can be an early surrogate marker for therapy response assessment. Residual ctDNA after neoadjuvant treatment was a significant predictor of metastatic recurrence and death. Personalized monitoring of ctDNA during the course of NAC is feasible and provides information that can be combined with imaging and pathology, and may help to optimize decision making for de-escalation or escalation of therapy. Larger studies are ongoing. ctDNA dynamics and pCRctDNA status at T0 and T1 (n=132)ctDNA status at T0, T1, and T2 (n=118)ctDNA-/-ctDNA+/-ctDNA+/+ctDNA-/-/-ctDNA+/-/-ctDNA+/+/-ctDNA+/+/+Total, n (%)24 (18)28 (21)80 (61)22 (19)24 (20)43 (36)27 (23)pCR, n (%)9 (38)15 (54)11 (14)9 (41)12 (50)8 (19)2 (7)No pCR, n (%)15 (63)13 (46)69 (86)13 (59)12 (50)35 (81)25 (93) Citation Format: Mark Jesus M Magbanua, Denise Wolf, Derrick Renner, Svetlana Shchegrova, Lamorna Brown Swigart, Christina Yau, Gillian Hirst, Hsin-Ta Wu, Ekaterina Kalashnikova, Antony Tin, Amy Delson, Douglas Yee, Angela DeMichele, Raheleh Salari, Angel Rodriguez, Bernhard Zimmermann, Himanshu Sethi, Alexey Aleshin, Paul Billings, Laura Esserman, Minetta Liu, Rita Nanda, Laura van ‘t Veer, I-SPY 2 Investigators. Personalized ctDNA as a predictive biomarker in high-risk early stage breast cancer (EBC) treated with neoadjuvant chemotherapy (NAC) with or without pembrolizumab (P) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD9-02.

4108 Background: Circulating tumor DNA (ctDNA) testing can be used for the assessment of molecular residual disease (MRD) in patients with early-stage or advanced colorectal cancer (CRC). Prospective evaluation of this methodology in clinical practice has been limited to-date. Methods: A personalized and tumor-informed multiplex PCR assay (Signatera 16-plex bespoke mPCR NGS assay) was used for the detection and quantification of ctDNA for MRD assessment. We analyze and present results from an ongoing early adopter program of ctDNA testing across the spectrum of CRC management. Results: Here we present a total of 250 patients with colon (n=200), rectal (n=40), and other lower gastrointestinal cancers (n =10; anal, appendiceal, small bowel). MRD positivity rates and ctDNA quantification (mean tumor molecules/mL) are shown in Table. ctDNA detection was significantly associated with stage of disease (p<0.0001 Chi-square: 70.33). Additionally, in patients with radiologically measurable active metastatic disease, ctDNA detection rate was 100%. On the contrary, patients with advanced/metastatic disease who had partial response to treatment or no evidence of disease (NED) showed 28.5% and 19.2% of ctDNA-positivity, respectively. Conclusions: This is the first large, real-world study reporting on the results from a clinically validated MRD assay. For the first time we delineate MRD rates and quantify ctDNA concentration in patients with early-stage and advanced CRC. Furthermore, we provide an initial readout that effective ongoing treatment in patients with CRC may be correlated with ctDNA clearance. Ongoing analysis expanded to a cohort of 1200 clinical cases including correlation with genomic and serial testing will be presented. [Table: see text]