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TPS259 Background: Despite currently approved therapies, most patients with metastatic colorectal cancer (mCRC) progress through all approved treatments and eventually succumb to their disease. Thus, novel therapies for chemotherapy-refractory mCRC are desperately needed. Inhibition of the DNA unwinding enzyme TOP1 is a well-characterized and clinically successful treatment strategy for mCRC. CBX-12 is a novel peptide-drug conjugate comprised of an exatecan warhead linked to a pH-Low Insertion Peptide (pHLIP). The principle behind this targeting mechanism is based on the Warburg effect, in which tumors establish a low pH extracellular environment. The pHLIP moiety of CBX-12 preferentially forms a unidirectional, transmembrane alpha helix in a low-pH extracellular environment. Thus, CBX-12 delivers its exatecan cytotoxic warhead preferentially into tumor cells. In mouse xenograft models, CBX-12 inhibited the HCT116 CRC xenograft model more potently than an equimolar dose of free exatecan. The phase 1 study of CBX-12 reported cytopenias as the predominant AEs and confirmed responses in several solid tumors including mCRC. Methods: This is a single-arm, phase 2 trial, with a Simon 2-stage design assessing CBX-12 for the treatment of chemotherapy-refractory mCRC. The primary objective is efficacy determined by RECIST v1.1 response rate. Secondary and exploratory objectives include evaluating the PK and PD as well as the progression-free survival (PFS) on CBX-12. Key inclusion criteria include: age ≥18 years, ECOG performance status ≤1, histologically or cytologically confirmed mCRC that is MSS/pMMR based on CLIA-approved testing, and progression on 2 or more lines of chemotherapy. This design requires 17 patients for stage 1, with termination if 1 or fewer objective responses are seen out of 17. If 2 or more patients out of 17 responds, then an additional 18 patients will be enrolled for stage 2. If 5 out of the total of 35 patients (14%) respond, then the trial would be declared successful. Correlative studies will include tumor plus peripheral blood PK to evaluate effectiveness of CBX-12 tumor targeting, ctDNA, and several tumor PD markers including TOP1-DNA trapping, SLFN11 expression, DNA damage, and apoptosis. The trial opened to enrollment on 8/21/25. Clinical trial information: NCT06730100 .

TPS256 Background: Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer (CC) to determine need for adjuvant chemotherapy (AC). However, circulating tumor DNA (ctDNA) represents a highly specific and sensitive approach (especially with serial monitoring) for identifying minimal/molecular residual disease (MRD) post-surgery in CC patients (pts), and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. CC pts who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may be spared the toxicities associated with AC. Furthermore, for CC pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal AC regimen has not been established. We hypothesize that for pts whose CC has been resected, ctDNA status may be used to risk-stratify for making decisions about AC. Methods: In this prospective phase II/III trial, up to 1,912 pts with resected stage IIB, IIC, and III CC will be enrolled. Based on the post-operative ctDNA status using personalized and tumor-informed assay (Signatera, bespoke assay), those who are ctDNA- (Cohort A) will be randomized to immediate AC with fluoropyrimidine (FP)+oxaliplatin (Ox) for 3-6 mos per established guidelines v serial ctDNA monitoring. Patients who are ctDNA+ post-operatively, or with serial monitoring (Cohort B), will be randomized to FP+Ox v more intensive AC with addition of irinotecan (I) for 6 mos. One cycle of chemotherapy is allowed while awaiting ctDNA testing results for cohort assignment. The primary endpoints for Cohort A are time to ctDNA+ status (phase II) and disease-free survival (DFS) (phase III) in the immediate v delayed AC arms. The primary endpoint for Cohort B is DFS in the FP+Ox v FP+Ox+I arms for both phase II and phase III portions of the trial. Secondary endpoints include prevalence of detectable ctDNA post-operatively, time-to-event outcomes (overall survival and time to recurrence) by ctDNA status, and the assessment of compliance to adjuvant therapy. Biospecimens including archival tumor tissue, as well as post-operative plus serial matched/normal blood samples, will be collected for exploratory correlative research. Active enrollment across the NCTN started in June 2022 with CCTG sites joining in August 2023. Current accrual (as of 9-4-2025): 967/1,912. Drs. Lieu and Dasari contributed equally to the development of this trial. Clinical trial information: NCT05174169 .

93 Background: Colorectal cancer (CRC) is the 4th most common cancer among men and women and roughly 2-4% of all CRCs occur in patients with a diagnosis of Lynch syndrome (LS), an autosomal dominant condition found to be the most common cause of hereditary CRC with estimated lifetime risk of developing CRC between 50-80%. LS results from mutations in one or more of 5 genes: MLH1, MSH2, MSH6, PMS2, and EPCAM, which lead to a deficiency in DNA mismatch repair ( dMMR ). Current guidelines suggest testing every CRC for microsatellite instability ( MSI ) or MMR gene expression using immunohistochemistry (IHC) to identify LS-related CRC. QuantCRC is a prognostic AI model that identifies important histological features of CRC and provides a recurrence prediction estimate useful for treatment decisions. It uses computational image analysis to extract quantitative features from digitized H&E stained pathology slides such as tumor grade, tumor-infiltrating lymphocytes, and other morphometric parameters. 4 It has been verified and validated in Aiforia (AI for image analysis) Platform using whole slide images and against reviews by independent pathologists from 8 hospitals. Our study sought to use QuantCRC to identify histological differences between those with MSI (confirmed LS), sporadic MSI , and microsatellite stability (MSS ) CRC to better help clinicians identify which patients would benefit from additional testing. Methods: We conducted a retrospective cohort study of patients with CRC whose pathology was analyzed at Mayo Clinic Arizona. Tumor characteristics were analyzed by QuantCRC and Receiver Operating Characteristic (ROC) curve analysis using Area Under the Curve (AUC) was used to see if QuantCRC could distinguish CRCs with MSI or LS. Results: Of the total 5132 patients with CRC, 1101 (21.5%) samples were MSI/dMMR with 468 (42.5%) of those having confirmed LS. The study had roughly equal parts men and there were more women with non-LS MSI (59%) than with LS or microsatellite stability. The QuantCRC model’s ROC analysis revealed an AUC of 0.83 for predicting MSI/dMMR among all patients with a sensitivity of 0.75 and a specificity of 0.79. AUC for predicting LS among all patients was 0.76 and of predicting LS among MSI/dMMR was 0.64. Conclusions: The QuantCRC model was useful in predicting MSI/dMMR status among all patients with CRC. It can be a helpful clinical tool when assessing which patients may benefit from additional genetic or IHC testing, especially in lower resource areas where molecular testing may be difficult to access or expensive relative to an H&E slide.

851 Background: Diffuse idiopathic skeletal hyperostosis (DISH) has been associated with increased risk of vertebral fractures in elderly men with prostate cancer. However, its potential role in the development of malignancies is poorly defined. In particular, the relationship between DISH and gastrointestinal (GI) cancers—including esophageal, gastric, colorectal, liver, biliary system, and pancreatic cancers—has not been examined. This study aimed to explore the risk of GI cancers among patients with DISH compared to those without DISH. We also assessed survival and incidence of vertebral fractures in these groups. Methods: Using the Mayo Clinic Platform (Full AMC1 dataset), we identified patients with and without a documented history of DISH. Outcomes included (1) prevalence and risk of GI cancers, (2) survival among GI cancer patients, and (3) vertebral fracture incidence. Relative risks (RRs) and hazard ratios (HRs) were calculated using SPSS20.0 and platform-based statistical tools, respectively. Kaplan–Meier survival analyses were performed to evaluate cancer survival outcomes. Results: A total of 6,189,860 patients were included, of whom 2,802 (0.05%) had DISH and 6,187,058 (99.95%) did not. Patients with DISH had a significantly higher prevalence of GI cancers compared with those without (RR = 1.63, 95% CI: 1.377–1.930). Survival analysis suggested worse outcomes among GI cancer patients without DISH (HR = 1.72, 95% CI: 1.25–2.35). Vertebral fracture incidence appeared lower among DISH patients, although low event numbers limit the reliability of this observation. Conclusions: DISH is associated with increased risk of GI cancers, while GI cancer patients without DISH may experience poorer survival. The observed trend toward lower vertebral fracture incidence among DISH patients should be interpreted cautiously due to limited event numbers. These findings highlight the importance of integrating musculoskeletal and oncologic perspectives in patient management and warrant further mechanistic and interventional studies. Survival analysis. Statistic Without DISH With DISH Patient Count 214,180 109 1 Month Survival 95.3% 98.2% 5 Month Survival 82.2% 87.9% 10 Month Survival 72.4% 85.1% 30 Month Survival 54.3% 74.1% 60 Month Survival 44.9% 60.6% Log-Rank 11.90 P-Value 0.00056 Hazard Ratio 1.72 (95% CI: 1.25 - 2.35)

837 Background: A recent randomized trial suggested that CR may influence ICI activity in patients with lung cancer. However, the same has not been established in GI cancers, where reports have shown mixed results with variable definitions of 'early' vs 'late' IT. We evaluated multiple approaches to assess the impact of CR on first-line ICI in GI malignancies. Methods: This retrospective study included patients from three Mayo Clinic sites (N=455). Both previously reported IT cutoffs and a new cutoff derived from ROC analysis were evaluated. Patients were categorized by the median of all ITs, the median of the first four ITs, and whether ≥20% of ITs occurred before the identified cutoff. Univariate and multivariate Cox regression (adjusting for age, MSI status, type of cancer, metastasis status, number of cycles, and receipt of chemotherapy with ICI) assessed associations with OS. KM analyses were performed to illustrate survival differences. The primary endpoint was OS. Results: When patients were categorized based on whether ≥20% of infusions occurred before 14:00 (ROC-derived cutoff), a significant association with OS was observed. On univariate analysis, early infusion timing was associated with improved survival (HR 2.30, 95% CI 1.58–3.32, p <0.001). This remained significant after multivariable adjustment (HR 2.11, 95% CI 1.41–3.16, p < 0.001). Median OS was 14.2 months in the early group vs 3.8 months in the late group (log-rank p < 0.001). Using previously defined cutoffs, categorization by the median IT of all infusions or the median of the first four infusions did not demonstrate a significant association with OS in either univariate or multivariate Cox regression analyses. Conclusions: These findings highlight the potential role of infusion timing as a chronotherapy factor in GI cancers. Given the retrospective design and heterogeneous population, prospective studies are warranted to validate this signal and clarify its clinical relevance. Baseline demographics of patients by infusion timing (early vs late). Variables Early N=412 (%) LateN=43(%) Total N=455(%) p-value Age <70 249(60.4) 21(48.8) 270 (59.3) 0.1 >70 163(39.6) 22(51.2) 185 (40.7) Gender F 118(28.6) 16(37.2) 134 (29.5) 0.3 M 294(71.4) 27(62.8) 321 (70.5) Cancer Type Gastroesophageal 109 (26.5) 8 (18.6) 117 (25.7) 0.1 Hepatocellular 159 (38.6) 24 (55.8) 183 (40.2) Biliary 86 (20.9) 4 (9.3) 90 (19.8) MSI-H 58 (14.1) 7 (16.3) 65 (14.3) Metastasis No 150 (36.4) 22 (51.2) 172 (37.8) 0.1 Yes 262 (63.6) 21 (48.8) 283 (62.2) Immunotherapy Cycle Number <6 189 (45.9) 33 (76.7) 222 (48.8) <0.001 >6 223 (54.1) 10 (23.3) 233 (51.2)

830 Background: Immune checkpoint inhibitors (ICIs) are standard therapy for MSI-H GI cancers. Lynch syndrome, caused by germline mutations in mismatch repair (MMR) genes, leads to MSI-H tumors and robust ICI responses, but its effect on irAEs remains poorly defined. Clarifying this risk may inform treatment selection and toxicity monitoring. Methods: We retrospectively reviewed MSI-H or MMR-deficient (dMMR) GI cancer patients (pts) treated with ICIs across Mayo Clinic (AZ, MN, FL) from January 2017 to June 2025. Eligible pts were identified using Mayo Data Explorer. Demographics, treatment, and irAEs (graded per CTCAE v5.0) were collected. Lynch status was determined by germline testing when available. Logistic regression estimated odds ratios (ORs) for any grade and grade ≥3 irAEs, adjusting for age, cancer type, prior chemotherapy, and treatment regimen. Results: A total of 209 pts with dMMR/MSI-H GI cancer were included: 61 with Lynch syndrome and 148 without. Lynch pts were younger (median 58 vs 76 years, p < 0.001) and more likely to have received prior chemotherapy (62% vs 43%, p = 0.009). Colorectal cancer was the predominant cancer type (74%), but Lynch pts had proportionally more non-colorectal GI cancers (15% vs 2.7%, p = 0.007). Overall, 29% of pts experienced an irAE, with rates significantly higher in Lynch vs non-Lynch pts (43% vs 24%, p = 0.005). The most frequent irAEs were gastrointestinal, endocrine, and dermatologic, followed by hepatic and pulmonary events. Grade ≥3 irAEs occurred in 16% overall, with no significant difference between groups (p = 0.124). In adjusted models, Lynch syndrome was independently associated with a higher risk of any grade irAE (OR 2.14, 95% CI 1.09 - 4.19, p = 0.026), while risk of severe irAEs was not increased (OR 1.55, 95% CI 0.64 - 3.59, p = 0.316). Lynch syndrome pts were more likely to have combination therapy (17% vs 6.8%, p = 0.029). However, there were no differences observed in any grade irAE between monotherapy and combination immunotherapy (OR 1.36, 95% CI 0.49 - 3.54, p = 0.535). Conclusions: Lynch syndrome is associated with a higher prevalence of any-grade irAEs among dMMR/MSI-H GI cancer pts treated with ICIs, though severe events were not increased. Incorporating Lynch status into immunotherapy planning may improve risk stratification and guide regimen selection.

83 Background: Colon cancer is among the leading causes of cancer-related morbidity and mortality globally, with an increasing incidence observed in younger populations. Lifestyle and metabolic risk factors seem to play an important role in this rising incidence. Glucagon-like peptide-1 (GLP-1) receptor agonists are widely used for the treatment of type 2 diabetes and obesity. Emerging evidence suggests that these agents may have potential anti-tumor activity as GLP-1 signaling may influence pathways involved in cell proliferation and inflammation. Our study aims to evaluate the impact of GLP-1 receptor agonists on outcomes among patients with colon cancer with comorbid obesity, exploring potential interactions between metabolic modulation and disease behavior. Methods: A retrospective cohort study was conducted using the US Collaborative Network TriNetX, covering January 2000 to December 2023, encompassing data from 105 global healthcare organizations. Adult patients aged 18 and above with colon cancer and comorbid obesity were identified and then stratified into two groups based on treatment with GLP-1 agonists or not. The two groups were then propensity-matched based on age, sex, race, and common comorbidities. We followed these patients for 5 years to assess outcomes, including overall mortality, myocardial infarction, sepsis, acute pancreatitis, need for mechanical ventilation and hemodialysis. Results: We identified 1986 patients with colon cancer and obesity who received GLP-1 receptor agonists, and 16384 patients with colon cancer and obesity who did not receive GLP-1 therapy. The average age was 68.8 years in the first cohort and 74.3 years in the second cohort. After propensity matching, each cohort consisted of 1983 patients with similar baseline characteristics and ethnicity distribution. Our analysis found that over 5 years, patients with colon cancer and obesity who received GLP-1 receptor agonists had a significantly lower risk of overall mortality (Hazard Ratio (HR): 0.461, 95% CI: 0.401 to 0.532, p-value < 0.001), myocardial infarction (HR: 0.827, 95% CI: 0.668 to 0.993, p-value =0.005), sepsis (Risk Difference: -3.48%, 95% CI: -4.774 to -2.185, p-value < 0.001), and need for mechanical ventilation (HR: 0.486, 95% CI: 0.321 to 0.739, p-value = 0.037). There was no statistically significant difference in the risk of acute pancreatitis and need for hemodialysis between the two subgroups. Conclusions: Our study revealed that patients with colon cancer and obesity who received GLP-1 receptor agonists had a significantly lower risk of mortality, myocardial infarction, sepsis, and need for mechanical ventilation. Further longitudinal cohort studies are imperative to better understand these associations and guide evidence-based clinical practice in this population.

817 Background: Universal germline sequencing is increasingly utilized in practice, but existing evidence and guidelines are based on studies in predominantly white populations. This study aims to compare the prevalence of genetic alterations in white vs underrepresented minority (URM) populations and assess incremental findings discovered with universal testing beyond current guidelines. Methods: This prospective, multicenter study analyzed genetic alterations in white and URM cohorts with primary GI malignancies receiving care at Mayo Clinic cancer centers between April 2018 and April 2025. Patients underwent germline sequencing using a next-generation sequencing (NGS) platform targeting over 80 genes. We compared the distribution of results between white and URM populations. Concordance with NCCN testing guidelines and incremental findings were assessed. Results: A total of 1128 patients were studied, of which 758 were white and 370 were URM, (47.6% Hispanic, 22.7% Black, 13.8% Asian, 10.5% American Indian, 0.8% Pacific Islander, and 6.8% other). Pathogenic variants (PGV) were more common in the white population (16.1% vs 9.2% P < 0.001). Variants of uncertain significance (VUS) were more common in the URM population (53.2 vs 43.5%, P<0.001). A total of 156 patients were found to have a PGV. PGVs outside primary cancer genes were more common in white patients (57.4% vs. 32.4%; p=0.0241). Incremental findings from universal testing were higher in white patients (66.4% vs 35.3%; p=0.0011). Conclusions: This study reveals a significant difference in the prevalence of PGV and VUS between white and URM patients with primary GI malignancies. The higher rate of PGVs in white patients and VUS in URM patients highlights potential inequities in both detection and interpretation of genetic results. These findings emphasize the need for broader representation in genetic databases to ensure equitable access to precision oncology. Screening guidelines met by patients with PGV. White (N=122) URM (N=34) Total (N=156) p value Did they meet NCCN testing guidelines for their primary cancer? 0.0991 Yes 87 (71.3%) 29 (85.3%) 116 (74.4%) No 35 (28.7%) 5 (14.7%) 40 (25.6%) Was the PGV outside of the primary genes recommended for their primary cancer? 0.0241 Yes 70 (57.4%) 11 (32.4%) 81 (51.9%) No 47 (38.5%) 22 (64.7%) 69 (44.2%) Incremental Finding 0.0011 Yes 81 (66.4%) 12 (35.3%) 93 (59.6%) No 41 (33.6%) 22 (64.7%) 63 (40.4%)

813 Background: Epidemiological data on gastrointestinal (GI) cancers in conflict-affected regions such as Syria are severely limited. Our study aims to fill in significant gaps in data by evaluating the demographics of Syrian patients diagnosed with new GI malignancies over a three-year period. Methods: This is a retrospective epidemiological study conducted at Al-Bairouni University Hospital – Syria’s national cancer center serving 60-70% of the country’s cancer patients. We included all patients diagnosed with GI malignancies (esophagogastric [EG], hepatocellular [HCC], biliary tract [BTC], pancreatic [PC], colorectal [CRC] cancers, and others) between Jan 2022 - Dec 2024. Data extracted from hospital records included sex, age at diagnosis, cancer stage, smoking status, and governorate of residence. Patients were grouped by disease group and year to assess annual trends. Institutional ethical approval was obtained to perform the study. Results: A total of 3,493 patients were diagnosed with GI cancers during the study period: 1,220 in 2022, 905 in 2023, and 1,368 in 2024 (Table 1). Across all years, a consistent male predominance was observed (60.1%). The average age at diagnosis was 59 years, 37.8% of patients were smokers, and 48.3% of all cases had advanced/metastatic disease at diagnosis. CRC (1,779) and EG (830) were the most common GI cancers. The highest patient loads originated from Damascus (17.6%) and Rural Damascus (17.5%), followed by central governorates such as Homs (9.7%) and Hama (9.3%). Notably, patients from more distant and underserved governorates such as Deir ez-Zor (7.0%), Aleppo (6.58%), and Al-Hasakeh (6.79%) accounted for a significant proportion of the GI cancers presenting to our center. Conclusions: To our knowledge, this study provides the first comprehensive multi-year dataset of GI cancers in Syria, with representation from all 14 governorates in the country. More than a third of our cohort were smokers and nearly half were diagnosed with advanced disease, demonstrating a need for public heath efforts to tackle tobacco use and improve screening & early detection. This dataset offers a foundation for future public health planning and research efforts in the region. Demographics of GI cancers diagnosed 2022-2024. Diagnosis 2022 Cases 2023 Cases 2024 Cases Total Cases Average Age Male Sex (%) Smokers (%) Advanced/Metastatic at diagnosis EG 311 217 302 830 56.1 519 (62.5%) 379 (45.7%) 370 (44.6%) HCC 88 46 61 195 59.2 134 (68.7%) 82 (42.1%) 116 (59.5%) BTC 34 43 54 131 58.4 69(52.7%) 40 (30.5%) 79 (60.3%) PC 118 122 160 400 58.4 249 (62.3%) 180 (45%) 247 (61.8%) CRC 620 444 715 1779 57.6 1008 (56.7%) 582 (32.7%) 805 (45.2%) Others (anal, small intestine, unknown primary) 49 33 76 158 55.5 75 (47.5%) 59 (37.3%) 69 (43.7%)

809 Background: Barriers to necessary care can pose a significant burden on patients with cancer, even more so in places of conflict. Following a devastating 14-year war in Syria, there is limited data published on access to cancer care and the impact that barriers to management have on our patients. We surveyed patients presenting for cancer care to better understand the challenges they faced. Methods: This cross-sectional study included adult patients with a confirmed gastrointestinal (GI) cancer diagnosis presenting to Al-Bairouni University Hospital for care. Data was collected through face-to-face interviews using a structured questionnaire adapted for the Syrian context. The survey covered six key areas: Demographic & Clinical, Healthcare System Barriers, Financial Barriers, Geographic & Security Barriers, Reasons for Diagnostic Delays, and Psychosocial Impact. Multivariate analysis via logistic regression was conducted to determine which responses were associated with a higher odds ratio (OR) of having a late-stage (III/IV) cancer diagnosis. Results: A total of 122 patients diagnosed with a GI cancer were enrolled. The mean age was 57.4 years (±11.2 SD), with a male predominance (68%, n=83). Advanced diagnostics (CT/MRI/biopsy) and radiation therapy were inaccessible for 55% (n =67) and 61% (n =74) of patients, respectively. Systemic therapy drugs were "rarely" or "never" available for 35% (n=43) of patients, and 12% (n=15) reported waiting over three months for an appointment. The costs of medications "greatly" or "very greatly" impacted 88% (n=107) of patients. Over two-thirds of patients reported that essential pain control medications (e.g., morphine) were "rarely" or "never" available (68%, n=83). Nearly two-thirds (65%, n =79) reported that security concerns "greatly" or "somewhat" affected their ability to access treatment. An overwhelming 87% (n=106) of patients reported a negative psychological impact from their treatment course. Patient responses associated with a higher OR of late-stage cancer diagnosis are present in the table. Conclusions: Patients in Syria with GI cancers face profound systemic, financial, geographic, and psychosocial challenges throughout their care journey. More than half were diagnosed at advanced stages, with diagnostic delays strongly linked to prolonged waiting times and financial strain. Financial toxicity was highly evident, resulting in treatment compromise and asset liquidation. This data should serve as a reference for future public health and humanitarian efforts in the region. Factors associated with late-stage (III/IV) diagnosis of GI malignancies (multivariate logistic regression). Variable Adjusted Odds Ratio (aOR) 95% Confidence Interval p-value Waiting Time First Oncology appointment >1 month 3.10 1.45 - 6.62 0.003 * Unemployed due to cancer 2.85 1.20 - 6.78 0.018 * Sold Assets to Finance Care 2.40 1.10 - 5.25 0.028 * *Statistically significant at p < 0.05.