Citations

Abstract Introduction and Purpose: Immune checkpoint signaling represents a major barrier to effective antitumor immunity by suppressing cytotoxic T-cell activity. Cytokine-inducible SH2-containing protein (CISH) is a genetically validated intracellular immune checkpoint that constrains cytotoxic T-cell and natural killer cell signaling. Emerging evidence supports a critical, T cell-intrinsic role for CISH in lymphoma. Despite strong biological validation, CISH targeting has thus far been limited to genetic manipulation in adoptive cell therapies. We sought to establish CISH as a drug-tractable target by discovering a first-in-class, cell-permeable small-molecule CISH inhibitor/degrader suitable for scalable immunotherapy development. Methods: CISH biology was characterized using datasets of patients with B-cell lymphoma and isogenic cellular models to define target-dependence benchmarks. Structure-guided small-molecule discovery was enabled through homology modeling and AlphaFold-based predictions of CISH structure. A focused library of covalent CISH binders was synthesized using systematic variation of SH2-engaging motifs and electrophilic warheads. Compounds were evaluated using biophysical binding assays, mass spectrometry–based covalent engagement, cellular degradation, and signaling readouts. Results: Cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) analysis identified CISH as one of the most highly expressed genes in intratumoral T cells associated with a poor prognosis in patients with non-Hodgkin lymphoma, supporting disease relevance and target enrichment. Genetic ablation or knockdown of CISH in a T cell model (KARPAS299) induced reproducible, target-dependent phenotypes, including enhanced S-phase entry and augmented STAT5 phosphorylation following IL-2 stimulation, establishing rigorous cellular benchmarks for pharmacologic modulation. We designed and synthesized over 50 candidate CISH binders incorporating covalent SH2-domain engagement. Multiple compounds showed direct binding to CISH by thermal shift analysis and selective covalent modification at Cys144 by mass spectrometry. Introduction of a masked phosphate motif significantly improved intracellular exposure, confirmed using a BODIPY-labeled analog. Lead compounds demonstrated target engagement by cellular thermal shift assay and induced rapid, concentration-dependent degradation of endogenous CISH within 4 hours in cells, while maintaining high selectivity over related SOCS family members, demonstrating both target engagement and specificity. Conclusions: This work establishes CISH as a chemically tractable intracellular immune checkpoint and reports the discovery of the first selective, cell-permeable small-molecule CISH degrader. These data provide a strong foundation for further structure activity relationship optimization and position CISH degradation as a promising drug discovery strategy to modulate T cell function and enhance antitumor immunity. Citation Format: Hao Xie, Xinyi Tang, Sujeewa Ranatunga, Stephen M. Ansell. Discovery of a small-molecule degrader targeting the intracellular immune checkpoint CISH [abstract]. In: Proceedings of AACR Drug Discovery and Development (AACR D3) Conference; 2026 Jul 21-24; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(14_Suppl):Abstract nr B049.

e15509 Background: Large language models (LLMs) are increasingly explored for oncology decision support, yet comparative evidence evaluating medical-specific versus general-purpose LLMs using expert-reviewed clinical cases is limited. We compared a medical-specific LLM (Google MedGemma 27B) with a general-purpose LLM (ChatGPT-5) using gastrointestinal (GI) and genitourinary (GU) oncology vignettes. Methods: This cross-sectional study evaluated 32 de-identified oncology vignettes (26 GI, 6 GU) created by a U.S. board-certified medical oncologist and informed by real-world cases. Vignettes included text-only information on the clinical context, description of pathology, tumor staging, biomarkers, and relevant comorbidities. Both LLMs were prompted to provide National Comprehensive Cancer Network(NCCN) guideline-based treatment recommendations, monitoring strategies, maintenance therapy considerations, and references, along with a self-reported confidence score (0–100). Board-certified U.S. medical oncologists independently reviewed outputs using a structured instrument; two disease specific expert oncologists evaluated each case. Outcomes included correctness and comprehensiveness (1–10 scales), hallucinations (factually fabricated or unsupported statements), NCCN traceability, potential patient harm, and clinician trust. Associations between accuracy and comprehensiveness were assessed using correlation coefficients. Inter-rater reliability was assessed using a two-way random-effects intraclass correlation coefficient (ICC). Results: ChatGPT-5 demonstrated higher mean correctness (8.65 vs 4.68) and comprehensiveness (8.68 vs 5.22) scores compared with MedGemma 27B. Accuracy and comprehensiveness were strongly correlated overall (Pearson r = 0.93, p < 0.001), with significant model-specific correlations (ChatGPT-5 r = 0.86, p < 0.001; MedGemma r = 0.77, p < 0.001). Hallucinations occurred less frequently with ChatGPT-5 (12.3% vs 65%), and NCCN-traceable recommendations were more common (75.4% vs 36.7%). Responses judged as potentially harmful occurred in 18.5% of ChatGPT-5 outputs versus 70% of MedGemma outputs. Clinician trust favored ChatGPT-5 (84.6% vs 15%). Inter-rater reliability improved with rater averaging (ICC(A,k): correctness 0.72; comprehensiveness 0.64). Conclusions: In expert-reviewed GI and GU oncology cases, ChatGPT-5 demonstrated higher clinical accuracy, comprehensiveness, and guideline alignment than a medical-specific LLM; however, a substantial rate of hallucinations and potentially harmful recommendations persisted across models. These findings underscore that, despite performance differences, current LLMs require rigorous clinician oversight and should not be used as standalone decision-support tools in oncology.

e15501 Background: CP is the backbone of first-line therapy for recurrent or metastatic ASCC. In practice, Q3-week CP has been explored as a potential alternative to the standard (d1,8,15 Q28-day cycle) dosing, though its efficacy is not known. This study evaluated CP scheduling and clinical survival associations in metastatic ASCC. Methods: This multicenter retrospective cohort study included patients with metastatic ASCC treated with first-line CP, identified using the Mayo Data Explorer database. Electronic health records were reviewed to collect baseline clinical characteristics, treatment regimens, responses, progression-free survival (PFS), and overall survival (OS). Descriptive statistics were used to summarize patient demographics. Survival was estimated using Kaplan–Meier methods. Multivariable Cox proportional hazards models were used to compare survival by dosing schedule, adjusting for age, ECOG performance status, HPV (p16) status, liver metastasis, and prior chemoradiation. Results: 54 patients treated between 2020-2025 with first-line CP for metastatic ASCC were included. Baseline patient demographics were balanced between dosing groups (Table 1). Median follow-up time was 26.2 months. For Q3-week CP (n = 21), median PFS and OS were 9.8 (95% CI 8.1, NR) and 27.0 (95% CI 15.7, NR) months, respectively, while median PFS was 6.5 (95% CI 4.5,15.3) months with standard CP (n = 33) and median OS was not reached (95% CI 11.2, NR). Response rate was 76% with Q3-week and 60.6% with standard CP (p = 0.23) dosing. Survival outcomes were similar when comparing Q3-week CP relative to standard CP dosing using multivariable analysis (PFS HR 0.68, 95% CI 0.33–1.41; OS HR 1.67, 95% CI 0.67–4.14). Higher ECOG and liver metastasis were independently associated with inferior outcomes, while HPV was associated with improved survival. Subsequent therapy patterns were similar between CP schedule groups. Ten patients (16.9%) received local therapy, and 24 of 28 patients with progression received further systemic therapy, including 21 (87.5%) treated with immunotherapy. Conclusions: Survival outcomes were similar across dosing schedules, suggesting Q3-week CP may be a reasonable alternative to standard CP, with potential to reduce treatment-related burden in metastatic ASCC. Future analysis will compare toxicity profiles between CP dosing schedules, including in combination with PD1 inhibitors given the results of the POD1UM-303 trial. Patient demographics (n=54). Variable Q3-week CP (n=21) Standard CP (n=33) p-value Sex Female 16 (76.2%) 24 (72.7%) 0.77 Male 5 (23.8%) 9 (27.3%) Age Median (Q1, Q3) 62 (50.5, 69) 64 (55.5, 70) 0.57 BMI Median (Q1, Q3) 27.1 (21.9, 34.4) 27.4 (22.5, 31.7) 0.72 ECOG 0 9 (42.9%) 11 (34.4%) 0.53 ≥ 1 12 (57.1%) 21 (65.6%) Confirmed HPV (p16) Positive 16 (76.2%) 24 (72.7%) 0.77 Prior chemoradiation Yes 17 (81.0%) 21 (63.6%) 0.17

3510 Background: Patients with RAS-mutated mCRC have limited treatment options. Chemotherapy in combination with bevacizumab (Bev) has been the standard first-line treatment for the past two decades, yet the prognosis for these patients remains poor. Onvansertib (Onv), a selective PLK1 inhibitor, has previously demonstrated synergy with chemotherapy in the second line setting. The Phase 2 randomized CRDF-004 trial evaluated onvansertib plus standard-of-care (SoC; FOLFIRI or FOLFOX with Bev) in as first-line RAS-mutated mCRC. Methods: Patients with first-line KRAS or NRAS mutant mCRC were randomized to SoC alone or SoC plus onvansertib (20 mg or 30 mg). The primary endpoint was objective response rate (ORR) as determined by a blinded-independent central review (BICR) using RECIST v1.1. Key secondary endpoints included progression-free survival (PFS), duration of response, and safety. PFS was assessed by BICR and investigator assessments combined. Results are presented in the intent-to-treat population (ITT). Results: At the data cutoff of 22 Jan 2026,110 patients were randomized with a median follow up of approximately 10 months. Baseline characteristics were relatively balanced across arms. Onv 30 mg + FOLFIRI + Bev demonstrated numerically higher ORR (n = 13/18, 72.2%, 95% CI: 46.5, 90.3) compared with the FOLFIRI + Bev control arm (n = 8/19, 42.1%, 95% CI: 20.3, 66.5), the FOLFOX + Bev control arm (n = 8/18, 44.4%, 95% CI: 21.5, 69.2) and the combined control arms (SoC: n = 16/37, 43.2%, 95% CI: 27.1-60.5). Onv 30mg + FOLFIRI + Bev demonstrated a p-value of 0.051 for confirmed ORR vs. SoC; and a p-value of 0.045 for the 6-month ORR compared to FOLFIRI + Bev (n = 10/18, 55.6%, 95% CI: 30.8-78.5 vs. n = 4/19, 21.1%, 95% CI: 6.1-45.6, respectively). The median PFS for the control arms was 10.97 months (95% CI: 7.52, NR) for FOLFIRI + Bev, 9.89 months (95% CI: 9.43, NR) for FOLFOX + Bev and 10.97 months (95% CI: 9.43-15.44) for the combined SoC arms. The median PFS in the Onv 30mg+ FOLFIRI + Bev arm was not reached (95% CI: 9.72-NR). The PFS HR of 30mg + Onv +FOLFIRI + Bev vs FOLFIRI + Bev was 0.38 (95% CI: 0.12-1.17) and vs SoC was 0.37 (95% CI: 0.13-1.02, p = 0.048). The clinical benefit from Onv treatment was further evidenced by the 12-month PFS rates, 61.9% (95% CI: 40.1, 95.8) in the Onv 30 mg + FOLFIRI + Bev arm vs. 28.4% (95% CI: 9.3, 86.9) in the FOLFIRI + Bev arm, and 30.1% (95% CI: 13.8-65.7) in the SoC. Onvansertib was well tolerated, with no unexpected toxicities observed; the most common grade ≥3 adverse event was neutropenia. PK data support moving forward with the onvansertib 30mg dose with FOLFIRI + Bev. Conclusions: Onvansertib plus FOLFIRI and bevacizumab demonstrated improved antitumor activity and manageable safety in first-line RAS-mutated mCRC. These results support further clinical and support planned confirmatory Phase 3 evaluation. Clinical trial information: NCT06106308 .

BACKGROUND Perineural spread (PNS) of colorectal carcinoma (CRC) is a rare and challenging diagnosis. Its clinical and radiological presentation is often subtle and can overlap with radiation-induced neuropathy and malignant nerve tumors, complicating timely diagnosis. The role of circulating tumor DNA (ctDNA) in the detection of PNS has not been previously described. OBSERVATIONS A 48-year-old man with a history of rectal cancer and perineural invasion presented with progressive, refractory sciatic neuropathic pain. Conventional surveillance imaging was initially negative despite subtle rising of carcinoembryonic antigen and ctDNA levels. Subsequent MRI revealed abnormalities of the lumbosacral plexus and sciatic nerve, and fascicular biopsy confirmed metastatic CRC involving the sciatic nerve, establishing the diagnosis of PNS. LESSONS This case highlights PNS as a rare but important consideration in patients with focal neuropathic symptoms and prior CRC. Circulating tumor DNA positivity may serve as an early indicator of occult tumor activity even within the nerves when imaging is equivocal. However, currently histopathological confirmation remains the only definitive method to distinguish PNS from alternative diagnoses and is essential to guide appropriate management. https://thejns.org/doi/10.3171/CASE25997

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.

103 Background: Clinicians spend significant time extracting and synthesizing information to risk-stratify and make adjuvant chemotherapy (AC) recommendations for CRC. By automating parts of this process, LLMs could help reduce documentation burden and variability in decision-making. Methods: We selected 144 stage III, pMMR CRC patients treated at Mayo Clinic (2017–2021). HIPAA-compliant Gemini-2.0-Flash-001 and GPT-4o extracted clinical variables (age, neuropathy grade, pathological stage) from EHRs and generated AC recommendations. Two approaches were compared: (1) a rule-based algorithm with nested if/else statements translating variables into NCCN-based recommendations, and (2) a dynamic LLM agent generating recommendations using a structured prompt informed by NCCN guidelines. Concordance with treating physicians was assessed, with disagreements reviewed by a blinded GI oncologist. Results: The dataset included 144 patients with median age 67 (IQR 66–68), 48.6% female. The LLM pipeline extracted neuropathy grade with 100% accuracy and pathological T/N stages with 99.3% accuracy. Concordance with physician recommendations was 93.1% for the rule-based algorithm and 62.5% for the LLM agent. In discordant cases, blinded adjudication by a GI oncologist favored the algorithm and LLM agent over physicians in most cases (Table 1). Conclusions: This exploratory work shows LLM agents can reliably extract variables and generate evidence-based treatment recommendations for stage III CRC. The high rate of expert preference for LLM recommendations in discordant cases is intriguing but limited by small sample size and possible adjudicator bias. Discordant physician recommendations reflect the complexity of decision-making, including patient preferences, performance status, comorbidities, and subtle findings not fully captured in EHRs. Rather than replacing judgment, we envision LLMs as decision support tools—analogous to an advanced trainee reviewing charts and presenting evidence-based recommendations to the attending physician with ultimate authority. Larger multi-institutional studies with multiple adjudicators are needed to validate these findings and clarify AI’s role in oncology. Patient characteristics, LLM extraction accuracy, and concordance with physician recommendations. Metric Result Total patients 144 Median age (IQR) 67 (66-68) Female (%) 48.6% LLM extraction accuracy – Neuropathy grade 100% LLM extraction accuracy – Pathological T and N stages 99.3% Primary Concordance – Rule-based algorithm vs. physician 93.1% Adjudicator preference of rule-based algorithm over treating physician for discordant cases 100% Concordance – LLM agent vs. physician 62.5% Adjudicator preference of LLM agent over treating physician for discordant cases 82.0%

PURPOSE Neoadjuvant immune checkpoint inhibitors (nICIs) have demonstrated high response rates in deficient mismatch repair/microsatellite instability–high (dMMR/MSI-H) gastroesophageal adenocarcinoma (GEA). The NEONIPIGA and INFINITY trials demonstrated high rates of pathologic complete response (pCR) in this patient population. Furthermore, the INFINITY trial explored the feasibility of managing these patients nonoperatively, demonstrating promising results. This study aimed to evaluate clinical outcomes of nICIs in resectable dMMR/MSI-H GEA, with a focus on the feasibility of nonoperative management (NOM). MATERIALS AND METHODS This retrospective cohort study included patients with resectable dMMR/MSI-H GEA and treated with nICIs ± surgery at the Mayo Clinic. Patients were identified from institutional records, and clinical data were retrospectively reviewed. Primary outcomes were clinical complete response (cCR) and pCR. Secondary outcomes included event-free survival (EFS), radiologic complete response (rCR), and immune-related adverse events (irAEs). RESULTS A total of 26 patients treated between April 1, 2017, and July 30, 2025, were identified. Nine patients (34.6%) underwent surgery, of whom six (66.7%) achieved pCR. Seventeen patients (65.4%) pursued NOM, with 10 (71.4%) of 14 evaluable patients achieving cCR and 14 (82.4%) of 17 evaluable achieving rCR. One patient who initially achieved cCR had a local recurrence on surveillance endoscopy and underwent salvage endoscopic resection. At a median follow-up of 19.3 months, 15 (88.2%) of 17 patients in the NOM cohort were alive and metastasis-free, with EFS rates of 87.3% at 12 and 24 months for all patients. irAEs occurred in nine patients (34.6%), with no grade ≥3 toxicities. CONCLUSION In this retrospective cohort study, nICIs led to high cCR and pCR rates in resectable dMMR/MSI-H GEA, supporting the use of immune checkpoint inhibitors in this setting and the feasibility of NOM in select patients.