Microsatellite Stable Colorectal Cancer Research Articles

Plasma versus tissue tumor mutational burden as biomarkers of durvalumab plus tremelimumab response in patients with metastatic colorectal cancer in the CO.26 trial.

Tissue derived tumor mutation burden (TMB) of ≥10 mutations/Mb is a histology agnostic biomarker for the immune checkpoint inhibitor (ICI) pembrolizumab. However, the dataset on which this was validated lacked colorectal cancers (CRCs), and there is limited evidence for immunotherapy benefit in CRC using this threshold. CO.26 was a randomized phase II study of 180 patients comparing durvalumab and tremelimumab (D+T, n=119 patients) versus best supportive care (BSC, n=61 patients). ctDNA sequencing was available for 168 patients (n=118 D+T, n=50), of which 165 had evaluable plasma TMB (pTMB). Tissue sequencing was available for 108 patients. Optimal thresholds for stratifying patients based on overall survival were determined using a minimal p-value approach. This report includes the final overall survival analysis. Tissue TMB ≥10 mutations/Mb was not predictive of benefit from D+T compared to BSC in microsatellite stable (MSS) metastatic CRC (HR 0.71 [95% CI:0.28-1.80], p=0.47). No tissue TMB threshold could identify a high TMB group that benefited from ICI. In contrast, plasma TMB (pTMB) ≥28 mutations/Mb was predictive of benefit from D+T (HR=0.34 [95%CI:0.13-0.85], p=0.022), as was clonal pTMB ≥10.6 mutations/Mb (HR=0.10 [95%CI:0.014-0.79], p=0.029) and subclonal pTMB ≥25.9/Mb (HR=0.20 [95% CI:0.061-0.69], p=0.010). Higher pTMB was associated with length of time on cytotoxic agents (p=0.021) and prior anti-EGFR exposure (p=2.44x10-06). pTMB derived from either clonal or subclonal mutations may identify a group more likely to benefit from immunotherapy, though validation is required. Tissue TMB provided no predictive utility for immunotherapy in this trial.

First-line oxaliplatin-based chemotherapy and nivolumab for metastatic microsatellite-stable colorectal cancer-the randomised METIMMOX trial.

We evaluated first-line treatment of metastatic microsatellite-stable colorectal cancer with short-course oxaliplatin-based chemotherapy alternating with immune checkpoint blockade. Patients were randomly assigned to chemotherapy (the FLOX regimen; control group) or alternating two cycles each of FLOX and nivolumab (experimental group). Radiographic response assessment was done every eight weeks with progression-free survival (PFS) as the primary endpoint. Cox proportional-hazards regression models estimated associations between PFS and relevant variables. A post hoc analysis explored C-reactive protein as signal of responsiveness to immune checkpoint blockade. Eighty patients were randomised and 38 in each group received treatment. PFS was comparable-control group: median 9.2 months (95% confidence interval (CI), 6.3-12.7); experimental group: median 9.2 months (95% CI, 4.5-15.0). The adjusted Cox model revealed that experimental-group subjects aged ≥60 had significantly lowered progression risk (p = 0.021) with hazard ratio 0.17 (95% CI, 0.04-0.76). Experimental-group patients with C-reactive protein <5.0 mg/L when starting nivolumab (n = 17) reached median PFS 15.8 months (95% CI, 7.8-23.7). One-sixth of experimental-group cases (all KRAS/BRAF-mutant) achieved complete response. The investigational regimen did not improve the primary outcome for the intention-to-treat population but might benefit small subgroups of patients with previously untreated, metastatic microsatellite-stable colorectal cancer. ClinicalTrials.gov number, NCT03388190 (02/01/2018).

Comparative effectiveness of immunotherapy and chemotherapy in patients with metastatic colorectal cancer stratified by microsatellite instability status.

Immunotherapy have demonstrated promising outcomes in patients with high microsatellite instability (MSI) (MSI-H) metastatic colorectal cancer. However, the comparative effectiveness of Immunotherapy and chemotherapy for patients with low MSI (MSI-L), and microsatellite stable (MSS) metastatic colorectal cancer remains unclear. To investigate immunotherapy vs chemotherapy for treatment of MSI-L/MSS metastatic colorectal cancer, and to evaluate the success of immunotherapy against chemotherapy in managing MSI-H metastatic colorectal cancer during a follow-up of 50 months. We conducted a retrospective cohort study using the National Cancer Database (NCDB) to evaluate the overall survival (OS) of patients with metastatic colorectal cancer treated with immunotherapy or chemotherapy. The study population was stratified by MSI status (MSI-H, MSI-L, and MSS). Multivariable Cox proportional hazard models were used to assess the association between treatment modality and OS, adjusting for potential confounders. A total of 21951 patients with metastatic colorectal cancer were included in the analysis, of which 2358 were MSI-H, and 19593 were MSI-L/MSS. In the MSI-H cohort, immunotherapy treatment (n = 142) was associated with a significantly improved median OS compared to chemotherapy (n = 860). After adjusting for potential confounders, immunotherapy treatment remained significantly associated with better OS in the MSI-H cohort [adjusted hazard ratio (aHR): 0.57, 95% confidence interval (95%CI): 0.43-0.77, P < 0.001]. In the MSS cohort, no significant difference in median OS was observed between immunotherapy treatment and chemotherapy (aHR: 0.94, 95%CI: 0.69-1.29, P = 0.715). In this population-based study using the NCDB, immunotherapy treatment was associated with significantly improved OS compared to chemotherapy in patients with MSI-H metastatic colorectal cancer, but not in those with MSI-L/MSS metastatic colorectal cancer. Further studies are warranted to determine the optimal therapeutic approach for patients with MSI-L/MSS metastatic colorectal cancer.

Genomic landscape of diploid and aneuploid microsatellite stable early onset colorectal cancer

Although colorectal cancer (CRC) remains the second leading cause of cancer-related death in the United States, the overall incidence and mortality from the disease have declined in recent decades. In contrast, there has been a steady increase in the incidence of CRC in individuals under 50 years of age. Hereditary syndromes contribute disproportionately to early onset CRC (EOCRC). These include microsatellite instability high (MSI+) tumors arising in patients with Lynch Syndrome. However, most EOCRCs are not associated with familial syndromes or MSI+ genotypes. Comprehensive genomic profiling has provided the basis of improved more personalized treatments for older CRC patients. However, less is known about the basis of sporadic EOCRC. To define the genomic landscape of EOCRC we used DNA content flow sorting to isolate diploid and aneuploid tumor fractions from 21 non-hereditary cases. We then generated whole exome mutational profiles for each case and whole genome copy number, telomere length, and EGFR immunohistochemistry (IHC) analyses on subsets of samples. These results discriminate the molecular features of diploid and aneuploid EOCRC and provide a basis for larger population-based studies and the development of effective strategies to monitor and treat this emerging disease.

Abstract CT007: Phase 1/2 trial of copanlisib in combination with nivolumab for microsatellite stable (MSS) colorectal cancer (CRC)

Abstract Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) is frequently mutated in CRC, leading to constitutive activation and enhanced cellular growth. PI3K also regulates immunity; inhibition of this pathway suppresses Tregs and myeloid derived suppressor cells resulting in enhanced anti-tumor immune responses. Murine experiments combining PD-1 and PI3K inhibition showed an increased CD8+ T cell:Treg ratio and improved survival compared to either alone. We launched a multicenter phase I/II investigation of copanlisib (PI3K inhibitor) and nivolumab (anti-PD-1) in 2 cohorts of patients with metastatic MSS CRC, Cohort 1: PIK3CA mutant (PI3KCAm) and Cohort 2: PIK3CA wild type (PIK3CAwt). From 2/2019 to 4/2022, 39 patients were enrolled: 6 in the phase 1 portion and 33 in phase 2 (22 PIK3CAm/17 PIK3CAwt). All patients had received at least 2 lines of prior therapy. Patient demographics and best treatment responses are in Table 1. There were no dose-limiting toxicities; toxicities were as expected and tolerable, most commonly hypertension in 16 (41%) patients and maculopapular rash in 4 (10%) patients. 3 patients in cohort 1 (14%) had partial responses (PR) and 3 had stable disease (SD): (range 1.7-4.7 mo.). One patient in Cohort 2 (6%) had a PR and 4 had SD: (range 3.8-7.4 mo.). Notably, all 4 responses have lasted more than 2 years. The trial incorporated robust translational correlates for mechanism interrogation with serial biopsies and blood draws. We will report circulating cytokine profiling, mass cytometry on PBMCs, and highly multiplexed immunofluorescence imaging (CyCIF) on paired pre- and on-treatment tissue specimens to i) dissect immune and PI3K pathway changes with treatment ii) correlate these to clinical responses and iii) determine baseline biomarkers of response and mechanism of effect. Overall copanlisib/nivolumab was well tolerated. The PIK3CAm CRC cohort met the primary endpoint for objective response rate but later than 6 months as responses were evolving. Table 1: Demographics and Best Treatment Responses of Patients Treated on NCT03711058: Study of Copanlisib and Nivolumab in MSS Colorectal Cancer Age Sex Race RAS-RAF status Best Response TMB Total (n=39) 58 (40-83) F: 53%(21), M: 47%(18) AA: 15%(6), AS: 8%(3), W: 77%(30) Altered: 67%(26), Wild type: 33%(13) PR: 10%(4), SD: 18%(7), PD: 72%(28) 5 (1-10) PIK3CA mutant (n=22) 57.5 (42-83) F: 73%(16), M: 27%(6) AA:23%(5), AS: 9%(2), W: 68%(15) Altered: 73%(16), Wild type: 27%(6) PR: 14%(3), SD: 14%(3), PD: 73%(16) 5 (1-10) Exon 9 mutation (n=13) 58 (45-83) F: 77%(10), M: 23%(3) AA: 15%(2), AS: 8%(1), W: 77%(10) Altered 85%(11), Wild type: 15%(2) PR: 8%(1), SD: 8%(1), PD: 85%(11) 7.9 (1-18) Exon 20 mutation (n=5) 62 (43-76) F: 80%(4), M: 20%(1) AA: 20%(1), W: 80%(4) Altered: 80%(4), Wild type: 20%(1) PR: 20%(1), SD: 20%(1), PD: 60%(3) 4 (3-8) Other (n=4) 46 (42-54) F: 50%(2), M: 50%(2) AS: 25%(1), AA: 50%(2), W: 25%(1) Altered: 75%(3), Wild type: 25%(1) PR: 25%(1), PD: 75%(3) 5.3 (3-7.6) PIK3CA wild type (n=17) 59 (40-81) F: 29%(5), M: 71%(12) AA: 6%(1), AS: 6%(1), W: 82%(15) Altered: 59%(10), Wild type: 41%(7) PR: 6%(1), SD: 24%(4), PD: 71%(12) 5.5 (1-9) AA: African American, AS: Asian, C: Caucasian, F: Female, M: Male, PD: Progressive disease, PR: Partial Response, SD: Stable disease Citation Format: Eric S. Christenson, Jeremiah A. Wala, Rose Parkinson, Natalie B. Collins, Christopher Jakubowski, Jea-Ren Lin, Hao Wang, Won Jin Ho, Sabrina Chan, Rachel Klein, Yvette Cetasaan, Emma Johnson, Maureen Berg, Jeffrey Meyerhardt, Benjamin Schlechter, Harshabad Singh, Peter K. Sorger, Marios Giannakis, Nilofer Azad. Phase 1/2 trial of copanlisib in combination with nivolumab for microsatellite stable (MSS) colorectal cancer (CRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT007.

Abstract CT276: Liberty-201: Maintenance fluoropyrimidine (FP) and bevacizumab with or without anti-lymphocyte activation gene-3 (LAG-3) antibody LBL-007 plus anti-programmed cell death protein-1 (PD-1) antibody tislelizumab (TIS) for patients (pts) with metastatic or unresectable microsatellite stable (MSS)/mismatch repair proficient (pMMR) colorectal cancer (CRC)

Abstract Background: LBL-007 is a monoclonal antibody targeting LAG-3, a receptor expressed on immune cells that negatively regulates T-cell proliferation and effector T-cell function. LAG-3 is frequently co-expressed with PD-1 on tumor-infiltrating T cells, and dual inhibition of LAG-3/PD-1 synergistically prevents tumor growth in mouse models. CRC is the second-highest cancer-related cause of death worldwide; pts diagnosed with metastatic CRC have a 5-year survival rate of 14%. Immunotherapy (IO) has only demonstrated clinical benefit in pts with microsatellite instability-high/MMR-deficient CRC, which accounts for 5% of CRC pts; however, improved therapy options for patients with MSS CRC remain limited. The combination of anti-LAG-3 + anti-PD-1 IO is currently being tested in clinical trials in pts with MSS CRC. Methods: This is a phase 1b/2, randomized, open-label study (NCT05609370). Pts with unresectable or metastatic CRC with locally or centrally confirmed pMMR or MSS status and no disease progression after induction treatment in first-line therapy are eligible. A maximum of 36 pts will be enrolled in phase 1b (safety run-in) to determine the recommended phase 2 dose. All pts will receive intravenous dual IO (LBL-007 + TIS) in combination with maintenance backbone (FP + bevacizumab). The dose of LBL-007 will be escalated from 150 mg every 3 weeks (Q3W) to 600 mg Q3W/400 mg Q2W using a Bayesian optimal interval design with informative prior. In phase 2, ~130 pts will be enrolled in the programmed death-ligand 1 (PD-L1)-positive group (tumor area positivity [TAP] ≥1%) and 60 patients in the PD-L1-negative group (TAP &amp;lt;1%). Pts with a PD-L1-positive status will be randomized 2:1:2 to receive dual IO + maintenance backbone (Arm A), LBL-007 + maintenance backbone (Arm B), or maintenance backbone only (Arm C). Pts with a PD-L1-negative status will be randomized 1:1 to receive dual IO + maintenance backbone (Arm D) or maintenance backbone only (Arm E). Treatment will continue until disease progression or unacceptable toxicity. The primary endpoint is safety in phase 1b and investigator-assessed progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 in phase 2. Secondary endpoints include overall survival, PFS2, overall response rate, duration of response, safety, pharmacokinetics, and immunogenicity. Exploratory endpoints include potential biomarkers (including but not limited to PD-L1 and LAG-3). Citation Format: Heinz-Josef Lenz, Ying Yuan, Vivian Li, Juan Zhang, Lubna Jamal, Xiao Lin, Fuxiang Zhu, John H. Strickler. Liberty-201: Maintenance fluoropyrimidine (FP) and bevacizumab with or without anti-lymphocyte activation gene-3 (LAG-3) antibody LBL-007 plus anti-programmed cell death protein-1 (PD-1) antibody tislelizumab (TIS) for patients (pts) with metastatic or unresectable microsatellite stable (MSS)/mismatch repair proficient (pMMR) colorectal cancer (CRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT276.

Abstract CT100: Safety and efficacy of AZD8853, an anti-growth and differentiation factor 15 (GDF15) antibody, in patients (pts) with advanced/metastatic solid tumors: First-in-human study

Abstract Background: GDF15 is overexpressed in solid tumors, with immunosuppressive effects on dendritic cells (DCs), T cells and myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. AZD8853 is an IgG1 monoclonal antibody that neutralizes GDF15. This Phase 1/2a, open-label study assessed AZD8853 monotherapy in previously treated advanced/metastatic non-small-cell lung cancer, microsatellite-stable colorectal cancer (MSS-CRC) and urothelial carcinoma (UC) (NCT05397171). Methods: Eligible pts were ≥18 years old with ≥1 measurable lesion per RECIST v1.1 and ECOG PS 0/1. AZD8853 was given IV Q3W until disease progression, unacceptable toxicity or consent withdrawal. The primary objective was safety including dose-limiting toxicities (DLTs). Secondary objectives included efficacy, pharmacokinetics (PK) and pharmacodynamics (PD [free serum GDF15]). Exploratory objectives included peripheral immune PD. Results: During dose escalation, 16 pts (15 MSS-CRC, 1 UC) received AZD8853 (300 mg, n=3; 1000 mg, n=6; 3000 mg, n=7). By June 6, 2023, all pts discontinued treatment and the study. Thirteen pts (81.3%) had treatment-emergent adverse events (TEAEs; Table); the most common were diarrhea (31.3%), abdominal pain (31.3%) and decreased appetite (25%). Eight pts (50%) had Grade ≥3 TEAEs and 6 (37.5%) had serious TEAEs; none treatment-related. There were no DLTs. No pts had responses by RECIST; 5 (31.3%) had stable disease and 11 (68.8%) had disease progression as best response. AZD8853 PK was linear with a half-life of 5-10 days, supporting Q3W dosing. GDF15 suppression was transient. There was no evidence of ctDNA clearance or a dose-dependent change in peripheral immune cells including CD8+ and CD4+ T cells, DCs and MDSCs. Conclusions: AZD8853 was well tolerated. No objective responses or PD effects were seen and GDF15 suppression was not sustained, therefore no further development is planned. TABLE 1. NAND Table. AZD8853 safety AZD8853 300 mg 1000 mg 3000 mg Total Safety, n (%) N=3 N=6 N=7 N=16 TEAEs 3 (100) 4 (66.7) 6 (85.7) 13 (81.3) Grade ≥3 TEAEs 1 (33.3) 3 (50.0) 4 (57.1) 8 (50.0) TRAEs 1 (33.3) 0 2 (28.6) 3 (18.8) Grade ≥3 TRAEs 0 0 0 0 Serious TEAEs 1 (33.3) 3 (50.0) 2 (28.6) 6 (37.5) TEAEs leading to discontinuation of AZD8853 0 1 (16.7)* 0 1 (6.3) TEAEs leading to death 0 1 (16.7)* 0 1 (6.3) DLTs, n (%) N=3 N=6 N=6 † N=15 DLTs 0 0 0 0 *Death due to serious AE of cardiac arrest, unrelated to AZD8853; pt had a history of coronary artery disease, coronary stenting, and pulmonary embolism.†One pt discontinued due to clinical progression prior to completing the DLT evaluation period and was not included in the DLT-evaluable set. DLTs, dose-limiting toxicities; TEAEs, treatment-emergent adverse events, TRAEs, treatment-related adverse events Citation Format: Benedito A. Carneiro, Olumide Gbolahan, Albiruni Abdul Razak, John F. Hilton, Arthur Lambert, John Hood, Michael Pluta, Veronique Bragulat, Elhan Sanai, Rakesh Kumar, Duncan Jodrell, Patricia LoRusso. Safety and efficacy of AZD8853, an anti-growth and differentiation factor 15 (GDF15) antibody, in patients (pts) with advanced/metastatic solid tumors: First-in-human study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT100.

Abstract CT101: Final results of the first-in-human study of the porcupine (PORCN) inhibitor zamaporvint (RXC004) in patients with advanced solid tumors

Abstract Background Dysregulated Wnt signalling drives several cancers through effects on proliferation, fibrosis and immune evasion. RXC004 is a novel oral small molecule inhibitor of protein-serine O-palmitoyltransferase (PORCN), which is required for the post-translational modification and activation of Wnt ligands. RXC004 has potential for efficacy in upstream Wnt pathway activated tumours: ~5% pancreatic cancer and ~8% microsatellite stable colorectal (CRC) cancer with RNF43 mutations or RSPO fusions, and tumors with high Wnt ligand expression. Methods In this Phase I study of RXC004 (NCT03447470), Module 1 investigated continuous monotherapy dosing, Module 2 investigated combination with nivolumab 480mg s.c. Q4W and Module 3 investigated intermittent monotherapy dosing (2 weeks on 1 week off). Patients received denosumab 120 mg s.c Q4W to prevent loss of bone mineral density (BMD), a known effect of Wnt inhibition. The primary objectives were safety and tolerability. Secondary objectives were PK and RECIST response. PD markers included on-treatment changes in: Wnt pathway and fibrosis biomarkers in paired skin biopsies; circulating immune subsets by flow cytometry; cytokine changes by Luminex, and changes in circulating-tumor DNA (ctDNA) levels by ddPCR. Results In Module 1, 25 patients (pts) with unselected advanced solid tumors (AST) received RXC004 between 0.5mg and 10mg QD. The RP2D was 2mg QD; at this dose the most common AEs were fatigue, diarrhoea, dysgeusia and decreased appetite; no grade 4/5 AEs or bone fragility events were reported whilst 1 pt had a RXC004-related grade 3 AE, 3 pts (50%) had a dose interruption and 1 had a dose reduction. The median T1/2 of RXC004 was 14.5h. 5 pts with upstream Wnt pathway activated tumors had stable disease (SD), in 1 case for 26 weeks with sustained reduction in ctDNA and no BMD loss. In Module 2, 14 patients with unselected AST received RXC004 at 1mg QD or 1.5mg QD with nivolumab. The AE profile was similar to Module 1. The RP2D was 1.5mg QD; at this dose 3 pts had a RXC004-related grade 3 AE, 6 pts (75%) had a dose interruption and 3 had a dose reduction, and 4 pts had SD. PK was similar to Module 1. In Module 3, 7 patients with upstream Wnt-activated AST received RXC004 2mg QD, 2 weeks on, 1 week off. The AE profile was similar to Modules 1 and 2. There were no RXC004-related Grade 3 AEs, 2 pts (29%) had a dose interruption and there were no dose reductions. PK and PD analyses confirmed time off target. 2 pts had SD; 1 pt with RSPO fusion small intestinal adenocarcinoma remained on treatment for 36 weeks, with sustained reduction in ctDNA and no BMD loss. Conclusions In patients with AST, RXC004 was safe and tolerated at doses up to 2mg QD as monotherapy and 1.5mg QD in combination with nivolumab, demonstrating differential disease control in upstream Wnt pathway activated tumours. Denosumab prevented loss of BMD. Intermittent RXC004 dosing was well tolerated with no detrimental impact on efficacy. Citation Format: Natalie Cook, Sarah Blagden, Juanita Lopez, Debashis Sarker, Alastair Greystoke, Noor MD Haris, Farasat Kazmi, Kaiser Anam, Ana Ortego Franco, Rille Pihlak, Louise Goodwin, David Wilson, Caroline Phillips, Jane Robertson, Helen Timmis, Craig Tilston, Simon A. Woodcock, Ruth Plummer. Final results of the first-in-human study of the porcupine (PORCN) inhibitor zamaporvint (RXC004) in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT101.

Activation of STING by the novel liposomal TLC388 enhances the therapeutic response to anti-PD-1 antibodies in combination with radiotherapy

Current immune checkpoint inhibiters (ICIs) have contrasting clinical results in poorly immunogenic cancers such as microsatellite-stable colorectal cancer (MSS-CRC). Therefore, understanding and developing the combinational therapeutics for ICI-unresponsive cancers is critical. Here, we demonstrated that the novel topoisomerase I inhibitor TLC388 can reshape the tumor immune landscape, corroborating their antitumor effects combined with radiotherapy as well as immunotherapy. We found that TLC388 significantly triggered cytosolic single-stranded DNA (ssDNA) accumulation for STING activation, leading to type I interferons (IFN-Is) production for increased cancer immunogenicity to enhance antitumor immunity. TLC388-treated tumors were infiltrated by a vast number of dendritic cells, immune cells, and costimulatory molecules, contributing to the favorable antitumor immune response within the tumor microenvironment. The infiltration of cytotoxic T and NK cells were more profoundly existed within tumors in combination with radiotherapy and ICIs, leading to superior therapeutic efficacy in poorly immunogenic MSS-CRC. Taken together, these results showed that the novel topoisomerase I inhibitor TLC388 increased cancer immunogenicity by ssDNA/STING-mediated IFN-I production, enhancing antitumor immunity for better therapeutic efficacy in combination with radiotherapy and ICIs for poorly immunogenic cancer.

Nivolumab plus ONC201 plus in microsatellite stable (MSS) metastatic colorectal cancer (mCRC) patients: a Brown University Oncology Research Group phase Ib/II study (BrUOG379).

Immune checkpoint inhibitors alone, or in combination with chemotherapy failed to provide meaningful clinical activity for patients with microsatellite stable (MSS) colorectal cancer (CRC). ONC201 is a small molecule that inactivates AKT and ERK signaling and actives the TRAIL pathway. Preclinical studies indicated potential benefits of combining ONC201 with checkpoint inhibitors. This is a phase Ib/II trial of ONC201 plus nivolumab for patient with MSS CRC who progressed on standard treatment. Enrolled patients received ONC201 plus nivolumab in a dose de-escalation fashion to determine the maximum tolerated dose (MTD). Additional patients were enrolled in the dose-expansion cohort. ONC201 at a dose of 625 mg was given orally at day -7 of cycle 1, followed by weekly dosing. Nivolumab was given every 2 weeks at 240 mg IV starting on day 1 of every cycle (cycle =28 days). The primary end point was dose-limiting toxicity (DLT) during the observation window (run-in dose day -7, cycle 1 to assessment pre-dosing cycle 2). The plan was to enroll 28 additional patients at the MTD so that a total of 34 patients would be treated at the MTD. Pharmacokinetics (PKs) and tumor biopsies were collected at several time points per study protocol. A total of 13 patients (8 patients in the dose escalation *6 evaluable*) were enrolled between December 4, 2019 and March 2021. All patients had received ≥2 previous lines of chemotherapy and had confirmed microsatellite stability or mismatch repair-proficient tumors. No DLTs were observed with 625 mg ONC201 in the first three patients. Three additional patients were enrolled at the same dose to confirm safety. Two patients progressed during the DLT period and had to be replaced. During the dose-expansion part, five patients were enrolled and none required dose reduction or modification. No objective tumor response was observed in the 13 treated patients. Disease progression was confirmed at the time of the first imaging evaluation at 8 weeks following cycle 2. Post discussion at the Data and Safety Monitoring Board (DSMB) on May 25, 2021, the principal investigator (PI) and Committee voted to close the study to new patient enrollment prior to reaching accrual of 34 patients, secondary to lack of efficacy. In this study of patients with advanced MSS CRC, combination ONC201/nivolumab was well-tolerated; objective responses to ONC201/nivolumab were not observed.

Pembrolizumab Plus mFOLFOX7 or FOLFIRI for Microsatellite Stable/Mismatch Repair–Proficient Metastatic Colorectal Cancer: KEYNOTE-651 Cohorts B and D

BackgroundThe phase 1b KEYNOTE-651 study evaluated pembrolizumab plus chemotherapy in microsatellite stable or mismatch repair-proficient (MSS/pMMR) metastatic colorectal cancer (mCRC). Patients and MethodsPatients with MSS/pMMR mCRC received pembrolizumab 200 mg every 3 weeks plus mFOLFOX7 (previously untreated; cohort B) or FOLFIRI (previously treated with fluoropyrimidine plus oxaliplatin; cohort D) every 2 weeks. Primary end point was safety; investigator-assessed objective response rate (ORR) per RECIST v1.1 was secondary and biomarker analysis was exploratory. ResultsThirty-one patients were enrolled in cohort B and 32 in cohort D; median follow-up was 30.2 and 33.5 months, respectively. One dose-limiting toxicity (grade 3 small intestine obstruction) occurred in cohort D. In cohort B, grade 3/4 treatment-related adverse events (AEs) occurred in 18 patients (58%), most commonly neutropenia and decreased neutrophil count (n = 5 each). In cohort D, grade 3/4 treatment-related AEs occurred in 17 patients (53%), most commonly neutropenia (n = 7). No grade 5 treatment-related AEs occurred. ORR was 61% in cohort B (KRAS wildtype: 71%; KRAS mutant: 53%) and 25% in cohort D (KRAS wildtype: 47%; KRAS mutant: 6%). In both cohorts, PD-L1 combined positive score and T-cell-inflamed gene expression profiles were higher and HER2 expression was lower in responders than non-responders. No association between tumor mutational burden and response was observed. ConclusionsPembrolizumab plus mFOLFOX7/FOLFIRI demonstrated an acceptable AE profile. Efficacy data appeared comparable with current standard of care (including by KRAS mutation status). Biomarker analyses were hypothesis-generating, warranting further exploration. ClinicalTrials.gov IdentifierClinicalTrials.gov; NCT03374254

Survival in metastatic microsatellite-stable colorectal cancer correlated with tumor mutation burden and mutations identified by next-generation sequencing

Survival in metastatic microsatellite-stable colorectal cancer correlated with tumor mutation burden and mutations identified by next-generation sequencing

Analysis of the Treatment for Advanced Microsatellite Stable Colorectal Cancer in Middle-Aged and Elderly People

Microsatellite stabilized (MSS) rectal cancer is a highly prevalent cancer in the middle-aged and elderly population. There exists some expertise in detecting and evaluating the chemotherapy effect in advanced colorectal cancer patients. Multiple studies have combined targeted therapy, chemotherapy, and immunotherapy as a breakthrough. Programmed cell death protein 1 (PD-1) inhibitors have certain therapeutic effects in the treatment of MSS rectal cancer patients. The combination of PD-1 inhibitors and furoquinib can improve the disease control rate (DCR) and progression- free survival (PFS) in colorectal cancer (CRC) patients with advanced MSS, and the adverse reactions are controllable. The combination of erlotinib hydrochloride and Xindilizumab was more effective in treating MSS-type colorectal cancer patients than clinical standard treatment. This study analyzes the various treatment methods for MSS-type CRC in middle- aged and elderly people to provide a reference basis in clinical practice.

Abstract 5056: Molecular characterization of microsatellite stable (MSS) colorectal cancer (CRC) patients with a BRAF V600E mutation

Abstract Introduction: A BRAFV600E mutation is an unfavorable prognostic biomarker for CRC and is associated with short-lived treatment response to BRAF and EGFR blockade. Anti-PD-1 therapies are ineffective in MSS CRC but demonstrate efficacy in combination with BRAF + EGFR inhibition for MSS BRAFV600E CRC. A comprehensive characterization of MSS BRAFV600E CRC as an immunologically distinct subpopulation of MSS CRC has not been performed. Here, we characterize the clinicopathological and transcriptomic features of MSS BRAFV600E CRC patients, relative to BRAFWT MSS CRC patients.Methods: De-identified records of 12,009 MSS CRC patients were retrospectively analyzed from the Tempus clinicogenomic database. CMS subtypes were derived using the CMScaller algorithm. Survival was assessed using Kaplan-Meier survival analysis with risk set adjustment (RSA) method; log-rank test was used to compare survival. Categorical and continuous variables were compared using chi-squared test and Wilcoxon rank sum test, respectively. Results: BRAFV600E was found in 5% (n=630) of the patients. Demographics and clinicopathological features varied significantly between the BRAFWT and BRAFV600E cohorts (Table 1). Relative to the BRAFWT cohort, BRAFV600E tumors were enriched for the immune-activated CMS1 signature (53% vs 11%, p&amp;lt; .001), PD-L1 detection (9.5% vs 3%, p&amp;lt;0.001), and CD8+ T-cell infiltration (4.6% vs. 2.5%, p&amp;lt;0.001). CMS4 was linked to an unfavorable prognosis in the BRAFWT cohort (HR=0.58 compared to CMS1, p=0.026), yet this was not observed in the BRAFV600E cohort (HR=2.60 compared to CMS1, p=0.083). Conclusions: BRAFV600E MSS CRC exhibited immune activation characteristics that were not observed in the BRAFWT group, including greater CMS1 status, PD-L1 expression, and CD8-T cell infiltration. Our findings support investigation of novel immune-based therapeutic strategies of MSS BRAFV600E CRC as an immunologically distinct subpopulation of MSS CRC. Cohort characteristics BRAFWT BRAFV600E P-value Demographics Age (median) 60 (51,69) 65 (55,74) &amp;lt;0.001 Ethnicity Not Hispanic or Latino 3,444 (83%) 200 (93%) 0.001 Hispanic or Latino 699 (17%) 16 (7.4%) Gender Female 4,771 (42%) 345 (55%) &amp;lt;0.001 Male 6,608 (58%) 285 (45%) Race White 5,050 (75%) 318 (87%) &amp;lt;0.001 Black or African American 888 (13%) 19 (5.2%) Other 517 (7.7%) 20 (5.4%) Asian 297 (4.4%) 10 (2.7%) Clinicopathology TNM stage I 61 (0.7%) 0 (0%) 0.1 II 388 (4.6%) 17 (3.2%) III 1,130 (13%) 88 (17%) IV 6,941 (81%) 424 (80%) Laterality Right 777 (15%) 89 (39%) &amp;lt;0.001 Transverse 193 (3.8%) 27 (12%) Left 2,326 (46%) 73 (32%) Rectum 1,761 (35%) 37 (16%) CMS CMS1 1,077 (11%) 307 (53%) &amp;lt;0.001 CMS2 3,067 (31%) 6 (1%) CMS3 1,777 (18%) 71 (12%) CMS4 3,920 (40%) 199 (34%) Immunology CD8 T-cell infiltration (median, IQR) 2.5% (0.0, 7.7) 4.6% (0.0, 9.4) &amp;lt;0.001 PD-L1 127 (3%) 22 (9.5%) &amp;lt;0.001 Citation Format: Ymke van der Pol, Binyam Yilma, Van K. Morris, Calvin Chao, Michelle Harris, Justin Guinney, Scott Kopetz. Molecular characterization of microsatellite stable (MSS) colorectal cancer (CRC) patients with a BRAF V600E mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5056.

Abstract 4095: Targeting alternative classes of tumor antigens to improve immunotherapy for microsatellite stable, mismatch repair-proficient colorectal cancer

Abstract Background: The clinical outcomes of immunotherapy for microsatellite stable (MSS) colorectal cancer (CRC) remains unsatisfactory. The development of more effective immunotherapies is hampered by limited knowledge of the appropriate target antigens, also considering the low burden of mutations generating neoantigens of these tumors. Alternative classes of MSS CRC antigens may provide actionable epitopes. Methods: We have characterized the immunopeptidome of 2 MSS CRC cell lines derived from the primary tumor (SW480) and a metastatic lymph node (SW620) of the same patient. Given the low mutational burden of MSS, we focused on peptides belonging to alternative sources of HLA-A*02 epitopes, such as proteasomal cis-spliced peptides derived from cancer testis antigens and linear epitopes derived from Human Endogenous Retroviruses (HERVs), which are frequently reactivated in CRC. Peptide immunogenicity was functionally validated based on their ability to expand HLA-A*02+ donor T cells (&amp;gt;3) specifically killing targets cells presenting the relevant peptides or HLA-matched CRC cell lines. In vivo epitope immunogenicity was verified by analyzing polyfunctional responses of human CD8+ T cells obtained from NSG-A2 mice humanized with A*02+ donor PBMCs and immunized with epitope-loaded nano-emulsions selectively targeting human Clec9A+ dendritic cells. Therapeutic exploitation of the novel epitopes was investigated by adoptive transfer of epitope-specific T cells in NSG-A2 mice injected with SW620 cells. Epitope-specific T cell responses were investigated in PBMCs from 10 MSS CRC patients and 7 donors. Results: Among &amp;gt;50,000 HLA-bound peptides identified by in depth immunopeptidomics analysis, 11 cis-spliced peptides and 5 HERV peptides were functionally validated as immunogenic. Epitope-specific T cells showed specific cytotoxic activity against SW480 and SW620 CRC cells. Globally, cis-spliced peptides were more immunogenic in vitro than HERV-derived peptides. The immunogenicity of both groups of peptides was confirmed in vivo in humanized mice. Adoptively transferred HERV or cis-spliced epitope specific T cells significantly inhibited the growth of SW620 cells in vivo, with cis-spliced epitope-specific T cells being more effective. Therapeutic efficacy of Clec9A-targeting vaccines exploiting these epitopes is currently under investigation. T cell responses specific for cis-spliced and HERV epitopes were detected in PBMCs from 3/4 MSS CRC HLA-A*02+ patients but in none of 4 HLA-A*02- MSS CRC patients or 7 healthy donors (4 HLA-A*02+ and 3 HLA-A*02-). Conclusions: We have identified and validated a new class of immunogenic HLA-A*02 epitopes derived from alternative classes of MSS CRC antigens. We also provide the proof of principle supporting their therapeutic exploitation to improve the management of these poorly immunogenic tumors. Citation Format: Riccardo Dolcetti, Bijun Zeng, Jingran Ye, Tima Shamekhi, Madeleine Harpur, Davide Moi, Sara Roth, Rob Ramsay, Divya Duscharla, Antony W. Purcell, Pouya Faridi, Roberta Mazzieri. Targeting alternative classes of tumor antigens to improve immunotherapy for microsatellite stable, mismatch repair-proficient colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4095.

Abstract 2505: Immune dynamics and response predictors to regorafenib, ipilimumab, and nivolumab (RIN) treatment in chemotherapy resistant microsatellite stable (MSS) metastatic colorectal cancer (mCRC)

Abstract Background: In our previous study, RIN therapy in MSS mCRC patients, excluding those with liver metastases, yielded a notable 36.4% objective response rate. RIN treatment was observed to remodel the local tumor microenvironment by enhancing immune infiltration, especially in responders. Systemic immunity, as assessed through peripheral blood analysis, showed that responders had lower baseline immune activity, which increased markedly post-treatment. Patients with liver metastases demonstrated a reduced CD4/CD8 T cell ratio, indicative of immunosenescence. Methods: Building on our prior research, we analyzed blood samples from 29 chemotherapy-resistant MSS mCRC patients undergoing RIN therapy, collected at baseline and after two consecutive treatment cycles. Two 28-marker spectral flow cytometry panels were used to assess immune senescence and cytokine production in lymphocytes. Additionally, T cell receptor repertoires and transcriptional profiles were analyzed using RNA sequencing from sorted non-naïve T cells. Results: The study unveiled distinct immunological profiles in MSS mCRC patient responders vs non-responders to RIN treatment. Responders demonstrated increased numbers of newly expanding CD8 T cell clones on-treatment, indicative of an active immune responses. In contrast, non-responders displayed evidence of increased DNA damage in circulating lymphocytes (T, B, and NK cells), as marked by elevated γ-H2AX levels. We also identified divergent cytokine production profiles patterns at baseline: T cells in non-responders demonstrated increased capacity for production of IL-2, IL-10, IL-4/-13, and IL-22, while production of IFN-γ in both T cells and NK cells correlated with improved outcomes. Notably, patients with liver metastases exhibited greater frequencies of senescent T cells, characterized by increased expression of senescence markers (SA-βGal, CD57, Granzyme B/K) and a reduction in CD27 and CD28 in CD4 T cells, along with an accumulation of terminally differentiated CD8 T cells both pre- and post-treatment. Additionally, RNA sequencing revealed an upregulation of FOXO1 related genes in non-naive T cells of responder patients, which is consistent with its important role for this pathway in attenuating senescence and maintenance of stem-like properties in T cells. Conclusions: The effectiveness of RIN therapy is associated with baseline functional potential of circulating T cells and an on-treatment expansion of T cell clonotypes. Pre-existing and persistent features of senescence and DNA damage in circulating lymphocytes may be a major barrier to RIN treatment efficacy in MSS colorectal cancer and should be validated further in future studies. Citation Format: Jian Ye, Chongkai Wang, Colt Egelston, Weihua Guo, Peter Lee, Marwan Fakih. Immune dynamics and response predictors to regorafenib, ipilimumab, and nivolumab (RIN) treatment in chemotherapy resistant microsatellite stable (MSS) metastatic colorectal cancer (mCRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2505.

A new strategy for immunotherapy of microsatellite-stable (MSS)-type advanced colorectal cancer: Multi-pathway combination therapy with PD-1/PD-L1 inhibitors.

Colorectal cancer (CRC) is a frequent gastrointestinal malignancy with high rates of morbidity and mortality; 85% of these tumours are proficient mismatch repair (pMMR)-microsatellite instability-low (MSI-L)/microsatellite stable (MSS) CRC known as 'cold' tumours that are resistant to immunosuppressive drugs. Monotherapy with programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) inhibitors is ineffective for treating MSS CRC, making immunotherapy for MSS CRC a bottleneck. Recent studies have found that the multi-pathway regimens combined with PD-1/PD-L1 inhibitors can enhance the efficacy of anti-PD-1/PD-L1 in MSS CRC by increasing the number of CD8+ T cells, upregulating PD-L1 expression and improving the tumour microenvironment. This paper reviews the research progress of PD-1/PD-L1 inhibitors in combination with cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) inhibitors, oncolytic virus, intestinal flora, antiangiogenic agents, chemotherapy, radiotherapy and epigenetic drugs for the treatment of pMMR-MSI-L/MSS CRC.

Abstract 5271: Pseudohypoxia by HIF-PHD inhibitors activates tumor immune response for MSS colorectal cancer

Abstract Purpose: Microsatellite-stable (MSS) colorectal cancer is resistant for immune therapy, necessitating the exploration of novel modalities for its conquest. Recent revelations have revealed the genetic upregulation of HIF-1α as a potential activator of CD8+ T-cells, enhancing an anti-tumor effect. Pseudohypoxia, characterized by normoxic upregulation of Hypoxia-Inducible Factor (HIF-1α), is known to be induced by iron chelators, including HIF-PHD inhibitors. In this study, we aimed to examine whether pseudohypoxia by HIF-PHD inhibitor can enhance immune response and elucidate the underlying mechanism. Method: Colon 26, SW480 and HT29 were used as murine and human MSS colorectal cancer model. Human and murine CD8+ T-cells were represented by Jurkat cells and isolated splenic CD8+ T-cells, respectively. HIF-PHD inhibitors Roxadustat and Vadadustat were used in the study, and a subcutaneous Colon 26 tumor model was established in BALB/c WT and nude mice. Hypoxic culture conditions were maintained for 48 hours at 2% O2. Results: Roxadustat and Vadadustat did not suppress the proliferation of cancer cells under conditions marked by HIF-1α upregulation. Roxadustat and Vadadustat suppress the colon 26 subcutaneous tumor growth in WT mice, the effect was cancelled in the nude mice. The treatment regimen was associated with an augmentation in the total number and effector-like subtypes of CD8+ T-cells (Tex) infiltrating the tumor. Combination therapy involving Roxadustat and PD-1 antibody synergistically inhibited tumor growth and was accompanied by an increase in PD-1lo, Ly108-, TIM-3+ CD8+ T-cells within the tumor microenvironment. Immunohistochemistry revealed that Interleukin-2 (IL-2) expression of murine spleen was stronger in Roxadustat than control group. Interestingly, HIF-PHD inhibitors induced the secretion of IL-2 from isolated CD3+ T-cells of murine spleens in ELISA, a phenomenon uniquely observed under pseudo-hypoxic conditions created by HIF-PH inhibitors, rather than actual hypoxia. This result indicates that pseudo-hypoxia may induce more robust hypoxic response than real hypoxia. Conclusion: The induction of pseudohypoxia by HIF-PHD inhibitors activates the tumor immune response for MSS colorectal cancer via induction of splenic IL-2. Citation Format: Toshiaki Ohara, Yuehua Chen, Yusuke Hamada, Seitaro Nishimura, Hotaka Kawai, Kazuhiro Noma, Hiroshi Tazawa, Toshiyoshi Fujiwara, Akihiro Matsukawa. Pseudohypoxia by HIF-PHD inhibitors activates tumor immune response for MSS colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5271.

Abstract 1189: Modulation of the MSS and MSI colorectal cancer immune microenvironment with FOLFOX and FOLFIRI -/+ anti-PD-1 immunotherapy

Abstract Metastatic colorectal cancer (mCRC) is a deadly disease with a five-year survival rate of 14%. Most patients receive 5-FU (F) and folinic acid (FOL) combined with oxaliplatin (OX), irinotecan (IRI), or both (OXIRI). Immune checkpoint inhibitors (ICIs) are effective against microsatellite instable (MSI) tumors, but 95% of mCRC tumors are microsatellite stable (MSS) and ICI-resistant. Though the primary targets of 5-FU, irinotecan, and oxaliplatin are well-understood, their effects on the tumor microenvironment (TME) remain incompletely characterized. Chemotherapy-mediated immune stimulation in MSS CRC has been observed in preclinical models and clinical trials. We hypothesize that combination chemotherapy treatment modulates the immune microenvironment of CRC -/+ ICI, with differences across subtype and treatment regimen. Chemotherapy-dependent changes in cancer cell gene expression, PD-L1 levels, cytokine secretion, and T cell activation were measured using in vitro models of MSS and MSI CRC. A preliminary evaluation of spleen and tumor T cells and dendritic cells (DCs) in murine models of MSS and MSI CRC after immunotherapy -/+ chemotherapy was conducted. CD8+ T cells, DCs, PD-L1, CD69, and GM-CSF expression were measured in clinical specimens of chemotherapy-treated MSS mCRC patients. In MSS CRC, FOX increased GM-CSF and activated CD8+ T cells in vitro and activated splenic CD8+ and CD4+ T cells in vivo. FOX and FIRI suppressed an anti-PD-1-mediated enhancement of type 1 cDCs in the tumor in vivo. FOLFOX was associated with increased tumor CD8+ T cells and decreased GM-CSF in MSS mCRC biopsies. FIRI treatment increased PD-L1 in vitro. FOLFIRI was not associated with increased tumor CD8+ T cells in MSS mCRC biopsies. In MSI CRC, FOX increased tumor CD8+ T cells in vivo. Here, we elucidate novel effects of clinically relevant chemotherapy combinations on the TME in MSS and MSI CRC. These data point to a FOX-specific mechanism by which CD8+ T cell infiltration into MSS mCRC tumors is enhanced, but their activation is halted potentially by GM-CSF suppression and/or type 1 cDC depletion in the TME. These findings contribute to our understanding of the mechanisms of chemotherapy-dependent immune modulation and bring the field closer to harnessing these effects for therapeutic gain. Citation Format: Lindsey Carlsen, Maximilian Pinho-Schwermann, Leiqing Zhang, Andrew Elliott, Kelsey E. Huntington, William J. MacDonald, Brooke Verschleiser, Laura Jinxuan Wu, Wafik S. El-Deiry. Modulation of the MSS and MSI colorectal cancer immune microenvironment with FOLFOX and FOLFIRI -/+ anti-PD-1 immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1189.

Abstract 6139: Genetic modifiers of KRAS-mutant colorectal cancer

Abstract Somatic driver mutations in KRAS are found in ~40% of colorectal cancers (CRCs) and are associated with worse outcomes. In the US, individuals of African ancestry with CRC are more likely to have tumors with KRAS mutations than individuals of European ancestry, even after considering differences in socioeconomic status and other risk factors. Germline variants can influence somatic mutation events and may provide a selective advantage such that a mutated cell is more likely to progress to a cancer. Germline variants have been found to associate with somatic mutations in a variety of tumors. Based on ancestry differences in KRAS tumor mutation frequency, we hypothesized that germline variants altering molecular pathways that support KRAS tumorigenesis will associate with KRAS-mutant status. To test this, we performed a two-step association study using KRAS mutation status as our phenotype in individuals with microsatellite stable CRC. First, we conducted a discovery analysis using genome-wide germline genotypes and somatic mutation data from 6,386 non-Hispanic White CRC patients from the Cancer Genome Atlas and the GECCO consortium, considering sex and tumor location as covariates. To select variants for additional study, we used in-silico tools, such as expression quantitative trait loci (eQTL), to predict how associated variants may alter gene expression and chromatin. After reviewing relevant genomic features, excluding SNVs with minor allele frequency &amp;lt;10% and pruning SNVs in linkage disequilibrium (r2&amp;gt;0.75), we identified candidate loci for a multi-ancestry independent validation analysis. In the discovery analysis, no variants met genome-wide significance thresholds (p-value &amp;lt;5x10-8), though 3 SNVs associated with KRAS mutation status with p-values &amp;lt;1x10-6 and 50 with p-values &amp;lt;1x10-5. Of these 50 SNVs, 21 met criteria for validation. We chose 80 additional SNVs (p-value &amp;lt;1x10-4) with predicted functional effect, for a total of 101 SNVs for analyses. In our preliminary validation analysis of 1,487 individuals grouped by self-reported race, no variants had a significant association in all populations. The rs726800 variant showed nominal association with KRAS mutation status (p-value=0.028) in self-reported non-Hispanic White individuals. This variant is within potential cis-regulatory distance of HS3ST3A1 and COX10-DT, both of which have been reported as cancer biomarkers. Nominal associations were identified in self-reported Black (n=7 SNVs) and Hispanic or Latino (n=3 SNVs) individuals, though both groups had limited sample sizes. Additional validation samples are being analyzed, as well as analysis with adjustment for genetic ancestry. Future functional studies of top candidate variants will add mechanistic insight. In summary, we identified germline SNVs that associate with KRAS somatic mutations in CRC and may inform the cellular context that supports development of colorectal tumors with KRAS mutations. Citation Format: Nijole P. Tjader, Johnny Ramroop, Tanish Gandhi, Peter T. Campbell, Andrew T. Chan, Steven Gallinger, Graham G. Giles, Marc J. Gunter, Tabitha A. Harrison, Michael Hoffmeister, Polly A. Newcomb, Shuji Ogino, Amanda I. Phipps, Conghui Qu, Robert E. Schoen, Andrew Pellatt, Michael O. Woods, Bethany Van Guelpen, Patrick Stevens, Heather Hampel, Ulrike Peters, Joseph P. McElroy, Amanda E. Toland. Genetic modifiers of KRAS-mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6139.