Immunotherapy For Pancreatic Cancer Research Articles

Anti-PD-L1 checkpoint inhibitor combined with nanocarrier-mediated cisplatin codelivery system for effective treatment of pancreatic cancer

Immune checkpoint inhibitor-based cancer immunotherapy has shown promise as a potential treatment in the clinic. It has been reported that anti-PD-L1 combined with cisplatin treatment can improve the antitumor effect. However, the therapeutic outcome is limited due to the abundance of tumor stroma in pancreatic cancer (PC), which prevented the penetration of cisplatin and anti-PD-L1 into tumor regions, thus impeding the effectiveness in the treatment of PC. In this study, a nanocarrier-mediated codelivery system of hyaluronidase and cisplatin was constructed, which can degrade the stroma and promote cisplatin and anti-PD-L1 to penetrate the tumor stroma into the deep tumor, so as to suppress PC effectively. When combined the cisplatin nanocarrier system BPEI-SS-Pt/HAase@CaP (BSP/H@CaP) with an immune checkpoint inhibitor to overcome the poor therapeutic outcome of PC, the results indicated that the therapeutic effect of BSP/H@CaP combined with anti-PD-L1 was better than that of BSP/H@CaP and single anti-PD-L1 group. Because the stroma is degrading, a higher amount of BPEI-SS-Pt and anti-PD-L1 can enter the tumor stroma and reach the inner depths of the tumor for immune stimulation, leading to a synergistically augmented chemotherapy and immunotherapy for PC. The above combination therapy is useful for clinical translation to overcome the treatment resistance of matrix-rich PC.

Abstract B064: Antigen-presenting type-I conventional dendritic cells facilitate curative checkpoint blockade immunotherapy in pancreatic cancer

Abstract The link between cancers and inflammation was first made by Rudolph Virchow more than a century ago when cancers were observed at sites with chronic inflammation. The host response to cancer shares many parallels with inflammation and wound healing process.Inflammation and tissue damage associated with pancreatitis can precede or occur concurrently with pancreatic ductal adenocarcinoma (PDAC). We demonstrate that in PDAC coupled with pancreatitis (ptPDAC), antigen-presenting type-I conventional dendritic cells (cDC1s) are specifically activated. Immune checkpoint blockade therapy (iCBT) leads to cytotoxic CD8+ T cell activation and eradication of ptPDAC with restoration of lifespan even upon PDAC re-challenge. Such eradication of ptPDAC was reversed following specific depletion of dendritic cells. Employing PDAC antigen-loaded cDC1s as a vaccine, immunotherapy-resistant PDAC was rendered sensitive to iCBT with a curative outcome. Analysis of the T-cell receptor (TCR) sequences in the tumor infiltrating CD8+ T cells following cDC1 vaccination coupled with iCBT identified unique CDR3 sequences with potential therapeutic significance. Our findings identify a fundamental difference in the immune microenvironment and adaptive immune response in PDAC concurrent with, or without pancreatitis, and provides a rationale for combining cDC1 vaccination with iCBT as a potential treatment option. Citation Format: Krishnan K Mahadevan, Allison M. Dyevoich, Yang Chen, Bingrui Li, Hikaru Sugimoto, Amari Sockwell, Kathleen McAndrews, Huamin Wang, Shabnam Shalapour, Stephanie Watowich, Raghu Kalluri. Antigen-presenting type-I conventional dendritic cells facilitate curative checkpoint blockade immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B064.

Abstract B033: MUC16 - Potential Target for Antibody-based Immunotherapy in Pancreatic Cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the most devastating and lethal cancer. PDAC patients with the current standard of care produce dismal overall survival benefits with high toxicities. Thus, there is an unmet clinical need to develop targeted therapeutics against PDAC. Approximately 50 to 70% of PDAC patients overexpress MUC16, which is associated with disease progression, metastasis, drug resistance, and poor patient survival. We demonstrated that MUC16 enhances PDAC tumor growth via binding and activating epidermal growth factor (EGF) receptor family members and its downstream target PI3K/AKT signaling pathways. Here, we show the efficacy of humanized anti-MUC16 antibody (huAR9.6) against MUC16-positive PDAC. Methods: We tested the in vitro efficacy of humanized anti-MUC16 antibody (huAR9.6) against MUC16+ PDAC cells, patient-derived xenografts (PDXs), and patient-derived organoids (PDOs). We evaluated the in vivo therapeutic efficacy of the huAR9.6 antibody in MUC16+ PDAC cells implanted in subcutaneous and orthotopic tumor models. Fucosylated and afucosylated huAR9.6 induced direct tumor-killing activity was evaluated by antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) with MUC16 positive PDAC cells. Results: Treatment with huAR9.6 reduced the in vitro growth, migration, invasion, and clonogenicity of MUC16+ PDAC cells and patient-derived organoids (PDOs). HuAR9.6 blocked MUC16-mediated ErbB and AKT activation in PDAC, PDOs, and PDX-derived cells. HuAR9.6 treatment induces ADCC and CDC against MUC16+ cells. Removing fucose residue on the N-glycans of the huAR9.6-IgG substantially increased huAR9.6’s ADCC activity. More importantly, huAR9.6 treatment caused PDAC regression in subcutaneous and orthotopic tumor models. Conclusion: The results of this study validate the translational therapeutic potential of huAR9.6 against MUC16-positive PDACs (detected in ∼ 50-70% of patients). Citation Format: Cory L Brooks, Prakash Radhakrishnan. MUC16 - Potential Target for Antibody-based Immunotherapy in Pancreatic Cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B033.

ZG16 enhances the maturation of dendritic cells via induction of CD40 and contributes to the antitumor immunity in pancreatic cancer.

Dendritic cells (DCs) are critical mediators of antigen priming and T-cell activation. Zymogen granule protein 16 (ZG16) is demonstrated as an anti-oncogene in T-cell mediated antitumor immunity, but its effect on DCs is largely unknown. Herein, we wonder whether ZG16 affects the activation of DCs in pancreatic cancer. Firstly, the increased ZG16 expression was observed during the maturation of DCs derived from mouse bone marrow or human peripheral blood. Then, overexpression of ZG16 or exogenous introduction of recombinant ZG16 protein induced the expression of MHC II, CD86, CD84, and CCR7 on the surface of DCs, thereby facilitating the secretion of proinflammatory mediators IL-1β, IL-6, TNF-α, and IL-12/p70, supporting the promoting effect of ZG16 on DC maturation. By establishing the subcutaneous and orthotopic mouse models of pancreatic cancer, we confirmed that intraperitoneal injection of recombinant ZG16 protein (Re-mZG16) could induce tumor regression by stimulating DC maturation and enhancing antitumor responses of CD4 + , CD8 + , PD-1 + , and Ctla4+ cells. Besides, Re-mZG16 in combination with gemcitabine showed a synergistic effect in the treatment of pancreatic cancer. Mechanistically, we demonstrated that ZG16 inhibited the ubiquitination and degradation of CD40, which depended on the lectin domain of ZG16. In conclusion, this study provided a novel insight into the role of ZG16-CD40 axis in DC-based immunotherapy for pancreatic cancer.

The Role of Tumor Microenvironment in Pancreatic Cancer Immunotherapy: Current Status and Future Perspectives.

Pancreatic cancer comprises different subtypes, where most cases include ductal adenocarcinoma (PDAC). It is one of the deadliest tumor types, with a poor prognosis. In the majority of patients, the disease has already spread by the time of diagnosis, making full recovery unlikely and increasing mortality risk. Despite developments in its detection and management, including chemotherapy, radiotherapy, and targeted therapies as well as advances in immunotherapy, only in about 13% of PDAC patients does the overall survival exceed 5 years. This may be attributed, at least in part, to the highly desmoplastic tumor microenvironment (TME) that acts as a barrier limiting perfusion, drug delivery, and immune cell infiltration and contributes to the establishment of immunologically 'cold' conditions. Therefore, there is an urgent need to unravel the complexity of the TME that promotes PDAC progression and decipher the mechanisms of pancreatic tumors' resistance to immunotherapy. In this review, we provide an overview of the major cellular and non-cellular components of PDAC TME, as well as their biological interplays. We also discuss the current state of PDAC therapeutic treatments and focus on ongoing and future immunotherapy efforts and multimodal treatments aiming at remodeling the TME to improve therapeutic efficacy.

The Road Ahead in Pancreatic Cancer: Emerging Trends and Therapeutic Prospects

This review explores the challenges and emerging trends in pancreatic cancer therapy. In particular, we focus on the tumor microenvironment and the potential of immunotherapy for pancreatic cancer. Pancreatic ductal adenocarcinoma, characterized by its dense stromal architecture, presents unique challenges for effective treatment. Recent advancements have emphasized the role of the tumor microenvironment in therapeutic resistance and disease progression. We discuss novel strategies targeting the desmoplastic barrier and immunosuppressive cells to enhance immune cell infiltration and activation. Recent clinical trials, particularly those involving novel immunotherapeutic agents and tumor vaccines, are examined to understand their efficacy and limitations. Our analysis reveals that combining immunotherapy with chemotherapy, radiation therapy, or drugs targeting epigenetic processes shows promise, improving overall survival rates and response to treatment. For instance, trials utilizing checkpoint inhibitors in combination with standard chemotherapies have extended disease-free survival by up to 6 months compared to chemotherapy alone. Importantly, vaccines targeting specific tumor neoantigens have shown the potential to increase patient survival. However, these approaches also face significant challenges, including overcoming the immunosuppressive tumor microenvironment and enhancing the delivery and efficacy of therapeutic agents. By providing an overview of both the promising results and the obstacles encountered, this review aims to highlight ongoing efforts to refine immunotherapy approaches for better patient outcomes.

Recent advances in immunotherapy for pancreatic cancer: a narrative review

Recent advances in immunotherapy for pancreatic cancer: a narrative review

12P STING-activable pyroptotic nanoparticles deliver GSDMDNT mRNA for in situ pancreatic cancer vaccination and immunotherapy

12P STING-activable pyroptotic nanoparticles deliver GSDMDNT mRNA for in situ pancreatic cancer vaccination and immunotherapy

MED12 loss activates endogenous retroelements to sensitise immunotherapy in pancreatic cancer

ObjectivePancreatic ductal adenocarcinoma (PDAC) stands as one of the most lethal cancers, marked by its lethality and limited treatment options, including the utilisation of checkpoint blockade (ICB) immunotherapy. Epigenetic dysregulation...

Probiotics functionalized with a gallium-polyphenol network modulate the intratumor microbiota and promote anti-tumor immune responses in pancreatic cancer

The intratumor microbiome imbalance in pancreatic cancer promotes a tolerogenic immune response and triggers immunotherapy resistance. Here we show that Lactobacillus rhamnosus GG probiotics, outfitted with a gallium-polyphenol network (LGG@Ga-poly), bolster immunotherapy in pancreatic cancer by modulating microbiota-immune interactions. Upon oral administration, LGG@Ga-poly targets pancreatic tumors specifically, and selectively eradicates tumor-promoting Proteobacteria and microbiota-derived lipopolysaccharides through a gallium-facilitated disruption of bacterial iron respiration. This elimination of intratumor microbiota impedes the activation of tumoral Toll-like receptors, thus reducing immunosuppressive PD-L1 and interleukin-1β expression by tumor cells, diminishing immunotolerant myeloid populations, and improving the infiltration of cytotoxic T lymphocytes in tumors. Moreover, LGG@Ga-poly hampers pancreatic tumor growth in both preventive and therapeutic contexts, and amplifies the antitumor efficacy of immune checkpoint blockade in preclinical cancer models in female mice. Overall, we offer evidence that thoughtfully designed biomaterials targeting intratumor microbiota can efficaciously augment immunotherapy for the challenging pancreatic cancer.

Noncoding Ribonucleic Acids (RNAs) May Improve Response to Immunotherapy in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is the seventh most common cause of cancer-related mortality. Despite different methods of treatment, nearly more than 90% of patients with PDAC die shortly after diagnosis. Contrary to promising results in other cancers, immune checkpoint inhibitors (ICIs) showed limited success in PDAC. Recent studies have shown that noncoding RNAs (ncRNAs) are extensively involved in PDAC cell-immune cell interaction and mediate immune evasion in this vicious cancer. PDAC cells recruit numerous ncRNAs to widely affect the phenotype and function of immune cells through various mechanisms. For instance, PDAC cells upregulate miR-301a and downregulate miR-340 to induce M2 polarization of macrophages or overexpress miR-203, miR-146a, and miR-212-3p to downregulate toll-like receptor 4 (TLR4), CD80, CD86, CD1a, major histocompatibility complex (MHC) II, and CD83, thereby evading recognition by dendritic cells. By downregulating miR-4299 and miR-153, PDAC cells can decrease the expression of NK group 2D (NKG2D) and MHC class I chain-related molecules A and B (MICA/B) to blunt the natural killer (NK) cell response. PDAC cells also highly express lncRNA AL137789.1, hsa_circ_0046523, lncRNA LINC00460, and miR-155-5p to upregulate immune checkpoint proteins and escape T cell cytotoxicity. On the other hand, ncRNAs derived from suppressive immune cells promote proliferation, invasion, and drug resistance in PDAC cells. ncRNAs can be applied to overcome resistance to ICIs, monitor the immune microenvironment of PDAC, and predict response to ICIs. This Review article comprehensively discusses recent findings regarding the roles of ncRNAs in the immune evasion of PDAC.

SPOP expression is associated with tumor-infiltrating lymphocytes in pancreatic cancer.

Speckle Type POZ Protein (SPOP), despite its tumor type-dependent role in tumorigenesis, primarily as a tumor suppressor gene is associated with a variety of different cancers. However, its function in pancreatic cancer remains uncertain. SPOP expression and the association between its expression and patient prognosis and immune function were evaluated using The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), The Tumor Immune Estimation Resource 2.0 (TIMER2.0) database, cBioportal, and various bioinformatic databases. Enrichment analysis of SPOP and the association between SPOP expression with clinical stage and grade were analyzed using the R software package. Then immunohistochemistry (IHC) was used to estimate the correlation between SPOP and tumor-infiltrating lymphocytes (TILs) in patients with pancreatic cancer. As part of our study, we assessed that SPOP was anomalously expressed in kinds of cancers, associated with clinical stage and outcomes. Meanwhile, SPOP also played a crucial role in the tumor microenvironment (TME). The expression level of SPOP was significantly correlated to tumor-infiltrating immune cells (TICs) in pancreatic cancer. Our study uncovered the potential corrections in SPOP with TICs, suggesting that SPOP may act as a biomarker for immunotherapy in pancreatic cancer.

Nano-enabled regulation of DNA damage in tumor cells to enhance neoantigen-based pancreatic cancer immunotherapy

Low-expression antigens, especially neoantigens, pose a significant challenge in immunotherapy for low immunogenicity pancreatic cancer. Increasing the tumor mutation burden is crucial to enhance the expression of tumor antigens and improve tumor immunogenicity. However, the incomplete intervention in DNA stability hampers effective elevation of the tumor mutation burden, thus reducing the probability of neoantigen. To address this issue, we have developed a novel nano-regulator that intervenes in the DNA stability of tumor cells, thereby enhancing tumor mutations. This nano-regulator comprises metal-organic frameworks (MOFs) encapsulating DNA damage agent doxorubicin and DNA damage repair inhibitor siRNA-ATR, enabling simultaneous induction of DNA mutations and inhibition of their repair. Importantly, this regulator, named as MOFDOX&siATR, can modulate the tumor gene expression profile, induce the production of neoantigens of Atp8b1, and enhance the immunogenicity of pancreatic cancer. The characteristics of DNA stability intervention by MOFDOX&siATR hold promise for augmenting the immune response in low immunogenic tumors, making it a potential nanomedicine for the treatment of pancreatic cancer.

Coordination engineering of FeCo dual single-atom nanozymes with photothermal-enhanced cascaded catalysis for efficient pancreatic cancer immunotherapy

Cancer immunotherapy holds great promise in improving therapeutic outcomes. However, its effectiveness is significantly hindered by the inadequate immunogenicity and potent immuno-suppressive nature of the tumor microenvironment (TME). Herein, we elaborately design an advanced iron-cobalt dual-single-atom nanozyme (FeCo-DA) with adjacent Fe-N/O-C and Co-N/O-C pair sites. This design aims to induce potent immunogenic cell death (ICD), ultimately enhancing cancer immunotherapy by activating the immune microenvironment. Compared to Fe and Co single-atom nanozyme, FeCo-DA demonstrated superior photothermal effects and cascaded catalytic performance by simultaneously mimicking peroxidase (POD), catalase (CAT), and glutathione oxidase (GSH-OXD). The cascaded catalysis not only augmented oxidative stress but also exacerbated the redox imbalance through sustainable generation of hydroxyl radicals (∙OH) and depletion of glutathione (GSH). The comprehensive in vitro and vivo experiments demonstrated that FeCo-DA effectively induced immunogenic cell death (ICD) by releasing damage-associated molecular patterns (DAMPs). The photothermal-enhanced cascaded catalytic therapy exhibited remarkable therapeutic effects on a mouse model of pancreatic cancer. This work highlights the potential of structure engineering in enhancing the efficacy of dual single-atom nanozyme for ICD-based cancer immunotherapy.

The Current Landscape of Clinical Trials for Immunotherapy in Pancreatic Cancer: A State-of-the-Art Review.

Pancreatic cancer remains a lethal malignancy with a 5-year survival rate below 6% and about 500,000 deaths annually worldwide. Pancreatic adenocarcinoma, the most prevalent form, is commonly associated with diabetes, chronic pancreatitis, obesity, and smoking, mainly affecting individuals aged 60 to 80 years. This systematic review aims to evaluate the efficacy of immunotherapeutic approaches in the treatment of pancreatic cancer. A systematic search was conducted to identify clinical trials (Phases I-III) assessing immunotherapy in pancreatic cancer in PubMed/Medline, CINAHL, Scopus, and Web of Science, adhering to PRISMA Statement 2020 guidelines. The final search was completed on May 25, 2024. Ongoing trials were sourced from ClinicalTrials.gov and the World Health Organization's International Clinical Trials Registry Platform (ICTRP). Keywords such as "pancreatic," "immunotherapy," "cancer," and "clinical trial" were used across databases. Gray literature was excluded. Phase I trials, involving 337 patients, reported a median overall survival (OS) of 13.6 months (IQR: 5-62.5 months) and a median progression-free survival (PFS) of 5.1 months (IQR: 1.9-11.7 months). Phase II/III trials pooled in a total of 1463 participants had a median OS of 12.2 months (IQR: 2.5-35.55 months) and a median PFS of 8.8 months (IQR: 1.4-33.51 months). Immunotherapy shows potential for extending survival among pancreatic cancer patients, though results vary. The immunosuppressive nature of the tumor microenvironment and diverse patient responses underline the need for further research to optimize these therapeutic strategies.

Emerging Nanotechnology in Preclinical Pancreatic Cancer Immunotherapy: Driving Towards Clinical Applications.

The high malignant degree and poor prognosis of pancreatic cancer (PC) pose severe challenges to the basic research and clinical translation of next-generation therapies. The rise of immunotherapy has improved the treatment of a variety of solid tumors, while the application in PC is highly restricted by the challenge of immunosuppressive tumor microenvironment. The latest progress of nanotechnology as drug delivery platform and immune adjuvant has improved drug delivery in a variety of disease backgrounds and enhanced tumor therapy based on immunotherapy. Based on the immune loop of PC and the status quo of clinical immunotherapy of tumors, this article discussed and critically analyzed the key transformation difficulties of immunotherapy adaptation to the treatment of PC, and then proposed the rational design strategies of new nanocarriers for drug delivery and immune regulation, especially the design of combined immunotherapy. This review also put forward prospective views on future research directions, so as to provide information for the new means of clinical treatment of PC combined with the next generation of nanotechnology and immunotherapy.

Type I conventional dendritic cells facilitate immunotherapy in pancreatic cancer.

Inflammation and tissue damage associated with pancreatitis can precede or occur concurrently with pancreatic ductal adenocarcinoma (PDAC). We demonstrate that in PDAC coupled with pancreatitis (ptPDAC), antigen-presenting type I conventional dendritic cells (cDC1s) are specifically activated. Immune checkpoint blockade therapy (iCBT) leads to cytotoxic CD8+ T cell activation and elimination of ptPDAC with restoration of life span even upon PDAC rechallenge. Using PDAC antigen-loaded cDC1s as a vaccine, immunotherapy-resistant PDAC was rendered sensitive to iCBT with elimination of tumors. cDC1 vaccination coupled with iCBT identified specific CDR3 sequences in the tumor-infiltrating CD8+ T cells with potential therapeutic importance. This study identifies a fundamental difference in the immune microenvironment in PDAC concurrent with, or without, pancreatitis and provides a rationale for combining cDC1 vaccination with iCBT as a potential treatment option.

A microphysiological system reveals neutrophil contact-dependent attenuation of pancreatic tumor progression by CXCR2 inhibition-based immunotherapy

Cancer cells recruit neutrophils from the bloodstream into the tumor tissue, where these immune cells promote the progression of numerous solid tumors. Studies in mice suggest that blocking neutrophil recruitment to tumors by inhibition of neutrophil chemokine receptor CXCR2 could be a potential immunotherapy for pancreatic cancer. Yet, the mechanisms by which neutrophils promote tumor progression in humans, as well as how CXCR2 inhibition could potentially serve as a cancer therapy, remain elusive. In this study, we developed a human cell-based microphysiological system to quantify neutrophil-tumor spheroid interactions in both “separated” and “contact” scenarios. We found that neutrophils promote the invasion of tumor spheroids through the secretion of soluble factors and direct contact with cancer cells. However, they promote the proliferation of tumor spheroids solely through direct contact. Interestingly, treatment with AZD-5069, a CXCR2 inhibitor, attenuates invasion and proliferation of tumor spheroids by blocking direct contact with neutrophils. Our findings also show that CXCR2 inhibition reduces neutrophil migration toward tumor spheroids. These results shed new light on the tumor-promoting mechanisms of human neutrophils and the tumor-suppressive mechanisms of CXCR2 inhibition in pancreatic cancer and may aid in the design and optimization of novel immunotherapeutic strategies based on neutrophils.

The impact of KRAS mutations on the clinical outcome and immune response following immunotherapy for pancreatic cancer

The impact of KRAS mutations on the clinical outcome and immune response following immunotherapy for pancreatic cancer

Impact of concurrent antibiotics on survival with immunotherapy in metastatic colorectal and pancreatic cancer.

2609 Background: The interplay between antibiotics and the microbiome has been hypothesized to modify the immune response to cancer and may negatively affect immune checkpoint inhibitor (ICI) efficacy. Methods: We retrospectively reviewed concurrent antibiotics received in the randomized phase II Canadian Cancer Trials Group (CCTG) CO.26 and PA.7 clinical trials. CO.26 evaluated dual programmed death-ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibition (with durvalumab and tremelimumab) versus best supportive care only (BSC) in metastatic refractory colorectal cancer (CRC). PA.7 evaluated gemcitabine and nab-paclitaxel +/- durvalumab and tremelimumab in metastatic pancreatic ductal adenocarcinoma. In CO.26, T cell receptor sequencing (TCR-seq) was available at baseline and week 8. Results: In CO.26 (n=180), median (range) age was 65 (36-87) years, 33% (n=59) were female, and 29% (n=50) were ECOG 0. Concurrent exposure to antibiotics was associated with improved overall survival (OS) (7.4 vs 6.2 months, adjusted hazard ratio (aHR) 0.66 (95% confidence interval (CI) 0.46-0.93), p=0.018) in patients with metastatic CRC who received ICIs, but not in patients who received BSC (3.5 vs 4.5 months, HR 1.49 (95% CI 0.81-2.73), p= 0.20); (p-interaction=0.094). In antibiotic class analysis, concurrent exposure of ICIs to fluoroquinolones (9.4 vs 6.2 months, aHR 0.50 (95% CI 0.30-0.82), p=0.0067), but not penicillins or cephalosporins, was associated with improved OS. There was no difference in RAS/RAF status or tumor mutation burden in patients who received antibiotics/fluoroquinolones or not. The results were consistent when also controlling for TMB (antibiotics aHR 0.63 (0.44, 0.91), p=0.013; fluoroquinolones aHR 0.51 (0.31, 0.84), p=0.009). Patients treated with antibiotics did not have a different TCR diversity or clonality between baseline and 8 weeks (p=0.37 and p=0.47) compared to those who did not receive antibiotics (p=0.26 and p=0.60). In PA.7 (n=180), median (range) age was 65 (29-84) years, 48% (n=87) were female, and 24% (n=44) were ECOG 0. Antibiotics were not associated with OS in patients who did/did not receive ICIs (9.7 vs 10.8 months, HR 0.97 (95% CI 0.64, 1.46), p=0.87; 7.4 vs 10.3 months HR 1.22 (95% CI 0.72, 2.09), p=0.46, respectively). Fluoroquinolones were also not associated with OS regardless of whether or not the patient received ICI therapy (10.9 vs 9.8 months, HR 0.74 (95% CI 0.47, 1.15), p=0.18; 7.2 vs 10.2 months, HR 1.18 (95% CI 0.62, 2.27), p=0.62). Conclusions: Concurrent exposure to antibiotics, and specifically fluoroquinolones during ICI therapy was associated with a statistically significant improvement in OS in patients with metastatic CRC, but not metastatic pancreatic cancer. This is discrepant from prior reports in other tumor types and suggests that the gut microbiome may impact ICI efficacy uniquely in patient with CRC. Clinical trial information: NCT02870920 , NCT02879318 .