Mismatch Repair Deficient Cancer Research Articles

Abstract 5149: Extracellular matrix remodeling in metastatic mismatch repair deficient endometrial cancer:Implications for immune checkpoint inhibitor response prediction

Abstract Mismatch repair deficient (MMRd) status is a predictive biomarker for Immune checkpoint inhibitors (ICI) in endometrial cancer (EC), however, half of these patients (pts) do not respond. Most studies exploring biomarkers of response to ICI have focused on tumor or immune cell factors. We aimed to describe the extracellular matrix components of the tumor microenvironment (TME) in ICI-Responder (R) versus Non-Responder (NR) MMRd EC pts to identify new predictive biomarkers of response. Clinical data and outcomes of metastatic MMRd EC pts, treated with ICI (2016-2021), were retrospectively collected. Pts were classified as Rs (CR, PR, or SD ≥12 months) or NRs (PD or SD <12 months). Pre-ICI FFPE tumor samples were subjected to Biognosys UltraDeep TrueDiscovery™ Mass Spectrometry (MS) for identification of differentially regulated protein expression between R and NR. Criteria for protein candidate selection were p-value < 0.01 and average absolute log2 fold change (AVG Log ratio) > 0.58. Collagen was visualized on whole slides using Masson’s trichrome and quantified by Qupath. Collagen density was expressed as % positive surface in the intratumoral area. Second-harmonic generation (SHG) microscopy plus polarimetry (p-SHG) was used to estimate collagen content and describe the spatial orientation of fibrillar collagen in the intratumoral area. intraepithelial (ie) and stromal (s) CD3+ and CD8+ cells were quantified by Qupath. Non-parametric t-tests and Spearman’s rank coefficient (r) for linear correlation were used. Twenty-five tumor samples were included in the analysis: 17 from Rs and 8 from NRs. MS identified collagen type V alpha-2 (AVR Log ratio 2.9, p 0.008) and type XXII alpha-1 chains (AVR Log ratio 1.14, p 0.006) as significantly upregulated in NRs. Using spatial imaging, collagen density in the intratumoral area was significantly higher in NRs (median: 14.2% vs 4.6%, p 0.01). Intratumoral collagen density was positively correlated with collagen type V expression (r 0,54, p 0.016), and negatively correlated with ie and s CD3+ cell (r -0.39, p 0.054; r -0.4, p 0.048, respectively) and ie and s CD8+ cell (r -0.39, p 0.053; and r -0.29, p 0.166) infiltration. SHG confirmed that fibrillar collagen content in the tumor area was significantly greater in NRs (p 0.02). p-SHG revealed that NR tumors tended to show a highly disorganized collagen matrix. In contrast, a linear collagen pattern was associated with response to ICI: 89% of tumors displaying this pattern were Rs. Both MS and two different spatial approaches consistently demonstrated that increased collagen expression or density may serve as a potential predictive biomarker of resistance to ICI in MMRd metastatic EC, contributing to create an immunosuppressive TME. The spatial orientation pattern of collagen fibers may also be crucial in shaping immune TME and influencing the response to ICI. Citation Format: Juan Francisco Grau, Carole Aimé, Martin Mehnert, Elisa Yaniz-Galende, Catherine Genestie, Audrey Le Formal, Elodie Edmond, Antoine Amaury Lachaud, Patricia Pautier, Judith Michels, Sébastien Gouy, Amandine Maulard, Emeline Colomba-Blameble, Felix Blanc-Durand, Marie-Claire Schanne-Klein, Alexandra Leary. Extracellular matrix remodeling in metastatic mismatch repair deficient endometrial cancer:Implications for immune checkpoint inhibitor response prediction [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 5149.

Abstract 4244: Clinical response assessment of immune checkpoint inhibitors in mismatch repair-deficient endometrial cancer using a T cell organoid coculture system

Abstract Endometrial cancers with the mismatch repair deficiency (MMR-D) phenotype exhibit characteristics such as an increased burden of tumor mutations and the presence of tumor-infiltrating lymphocytes (TILs) involved in tumor invasion. While monotherapy using immune checkpoint inhibitors (ICIs) has shown clinical improvement in MMR-D endometrial cancer (EC), observed response rates ranging from 30% to 50% suggest the existence of inherent resistance mechanisms. One notable feature of MMR-D tumors is the high proportion of tumor-infiltrating lymphocytes (TILs) encompassing various lymphocytes with diverse effects on immune interactions. Therefore, we aim to assess the feasibility of a self T-cell-tumor organoid co-culture platform for individual MMR-D endometrial cancer patients. We provide evidence that co-culturing self-tumor organoids with peripheral blood lymphocytes can be utilized to evaluate ICI responsiveness in MMR-D endometrial cancer patients. The application of a specific T-cell organoid co-culture platform to a cohort of patient resistant to monotherapy ICIs offers a means to anticipate the timing for minimal immunotherapeutic intervention and the appropriate timing for combination therapy. Citation Format: Ju Hee Oh, Eun Hye Choi, Ji Eun Lee, Eun Ji Nam. Clinical response assessment of immune checkpoint inhibitors in mismatch repair-deficient endometrial cancer using a T cell organoid coculture system [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 4244.

Abstract 6673: Tumor microbial burden is regulated by mast cells and determines immunotherapy responses

Abstract Immune checkpoint inhibitors (ICI) have notably improved overall survival rates across various cancers, particularly in cases of mismatch repair deficient cancer (MMRd). However, numerous factors influence patient response following ICI treatment. Beyond genetic factors, mutations, and levels of immune cell infiltration, several studies highlight the correlation between the gut microbiome and treatment response rates. Furthermore, specific bacterial compositions have been observed to shift during therapeutic interventions. Notably, studies have demonstrated that patients who used antibiotics before and during ICI treatment exhibited lower progression-free survival and overall survival, serving as evidence for this association. Our previous investigations elucidated the impact of distinct tumor microbial burdens on modulating immune activation. Consequently, our hypothesis posits the substantive involvement of the interplay between tumor microbial burden and the immune system response to ICI treatment. We evaluated the presence of intra-tumoral microbes within Colorectal cancers (CRC) by examining TCGA data. Patients with elevated microbial levels demonstrated heightened immune activity and better survival rates. Using cybersport analysis, we validated increased mast cell infiltration in CRC patients with abundant microbes. Quantification involved assessing bacterial burden through 16s rRNA via FISH staining and mast cell counts using tryptase via IHC staining. Reducing bacterial load in MC38 cancer model, achieved by locally administering antibiotics, led to a diminished immune response when PD-1 was introduced to these mice. Cross-referencing TCGA data, we identified upregulated genes in CRC patients with high microbial burden and downregulated genes in mice receiving local antibiotics after MC38 cell implantation. The common genes were associated with immune responses, suggesting a strong correlation between bacterial burden and immune activity in CRCs. In conclusion, the high burden of bacteria in CRC improves immune response to ICI and increases the infiltration of mast cells, which all contribute to better survival rates. Citation Format: Hajar Rajaei, Jeong-Hoon Jang, Haoyue Liu, Erika Y. Faraoni, Olivia Le Roux, Vidhi Chandra, Virginia Tahan, Le Li, Erick Riquelme, James Robert White, Luis A. Diaz Jr., Florencia McAllister. Tumor microbial burden is regulated by mast cells and determines immunotherapy responses [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 6673.

Systematic Review of Neoadjuvant Immunotherapy for Mismatch Repair Deficient Locally Advanced Colon Cancer: An Emerging Strategy.

In April 2023, the National Comprehensive Cancer Network endorsed neoadjuvant immunotherapy for select patients with non-metastatic mismatch repair deficient colon cancer. Approximately 15% of incident colon cancers are mismatch repair deficient, resulting in a distinct molecular subtype with high microsatellite instability that is responsive to immune checkpoint inhibition. To describe the existing evidence supporting neoadjuvant immunotherapy for mismatch repair deficient, microsatellite unstable non-metastatic colon cancer. A medical librarian performed PubMed, Embase, and Web of Science searches most recently on April 24, 2023. The PubMed search was re-run on September 26, 2023, to identify any additional studies published during the interim from April to September 2023. Two authors screened titles and abstracts in the published studies. The inclusion criteria were (1) English-language; (2) adults with primary cancer of the colon; (3) non-metastatic disease; (4) neoadjuvant immunotherapy; (5) reporting on 10 or more cases. Neoadjuvant immunotherapy. Safety (Grade 3+ treatment related adverse events) and efficacy (complete pathologic responses). From 7,691 studies identified, 6,370 were screened, and 8 included. Various agents, dosing regimens, and treatment durations were employed, with durations of immunotherapy ranging from 1-16 cycles. Complete R0 resections were consistently achieved in 98%-100% of resections. Of patients who received neoadjuvant immunotherapy and underwent resection, 50%-91% had ypT0N0 pathology. The safety profiles were generally favorable, with Grade 1-2 treatment-related adverse events (mostly immune-related) during immunotherapy reported in 22.2%-70% of patients. Postoperative complications following neoadjuvant immunotherapy were reassuring, with no severe complications reported. Small number of heterogeneous and uncontrolled studies precluding a meta-analysis. Neoadjuvant immune checkpoint inhibition is associated with high rates of pathologic complete responses in locally advanced colon cancer. The literature is limited, particularly for postoperative outcomes, and more studies are needed to understand the safety and positioning of these regimens in the neoadjuvant context.

Abstract B023: The role of ribosomal protein L22 in regulating the immune landscape in mismatch repair deficient endometrial cancers

Abstract The purpose of this study is to identify novel mechanisms of immune evasion in mismatch repair deficient endometrial cancers. Despite having a hypermutated phenotype that is proposed to lead to the accumulation of many neoantigens for immune recognition, our group has found that mismatch repair deficient endometrial cancers characterized by MLH1 protein loss display large variations in the number of tumors infiltrating CD8+ T cells (TILs) across different tumors. To better understand how variations in TILs arise in mismatch repair deficient endometrial cancers, we utilized human endometrial cancer samples from the UNCseq cohort. Immunohistochemistry (IHC) was used to identify expression patterns in proteins of interest across mismatch repair deficient endometrial cancers. To determine how expression patterns of proteins of interest correlate with TILs in our patient samples, Definiens Tissue Studio was utilized to quantify immunofluorescent CD8+ TILs in our mismatch repair deficient endometrial cancer cohort. Although upregulation of programmed death ligand 1 (PD-L1) expression is often cited as an explanation for low TILs, analysis of human data by our group shows that PD-L1 expression does not correlate with TIL numbers in mismatch repair deficient endometrial cancers. Interestingly, The Cancer Genome Atlas (TCGA) data reported that ribosomal protein L22 (RPL22) is mutated in ~50% of mismatch repair deficient endometrial cancers. We analyzed RPL22 by IHC and found that it was lost in 52% of our human mismatch repair deficient endometrial cancer cohort. Loss of various ribosomal proteins can alter translation efficiency of proteins critical for promoting immunosurveillance and the immune response in cancer. In our cohort, mismatch repair deficient endometrial cancers that have lost expression of RPL22 have lower numbers of CD8+ TILs. Preliminary data also show that human endometrial cancer cell lines that do not express RPL22 also do not express beta-2-microglobulin (β2M), a component of the major histocompatibility complex I (MHC-I) molecules that is necessary for neoantigen presentation to CD8+ T cells. Thus, we hypothesize that RPL22 loss in mismatch repair deficient endometrial cancers results in decreased translation of β2M and CD8+ T cell evasion. Moving forward, we speculate that RPL22 could be utilized as a predictive biomarker for immunotherapy response in mismatch repair deficient endometrial cancers. Citation Format: Macy L. Osborne, Hannah Atkins, Andrew B. Gladden, Russell R. Broaddus. The role of ribosomal protein L22 in regulating the immune landscape in mismatch repair deficient endometrial cancers [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr B023.

Abstract B026: Substratification of mismatch repair deficient (MMRd) endometrial cancers can provide prognostic and predictive refinement

Abstract Background: Mismatch repair deficient (MMRd) endometrial cancer (EC) represents one third of all ECs. Identifying patients with MMRd EC enables testing for Lynch Syndrome (LS) and access to FDA-approved immune checkpoint blockade (ICB) therapy. Recent data have highlighted the diversity within MMRd tumors, suggesting worse outcomes and lower response to ICB in patients with MLH1 loss. Our aim was to characterize a cohort of MMRd ECs to elucidate if clinically meaningful substratification of this molecular subtype (MLH1 loss vs. other MMRd) could be achieved. Methods: MMRd ECs were identified from retrospective institutional and population-based cohorts (1994-2016) with clinicopathologic data, immunohistochemistry (IHC) assessment of estrogen receptor (ER) and L1CAM and CTNNB1 mutation status recorded. Multiplex IHC for immune markers (CD3, CD8, CD79a, CD138, PD-1, PD-L1, FoxP3, IDO-1) was assessed and compared in patients with MLH1 loss or PMS2/MLH1 loss (when 2 antibody MMRd testing performed) vs. isolated MSH2, MSH6, PMS2 or MSH2/MSH6 loss (remainder of MMRd). Results: 655 MMRd ECs were identified, 52% of cases assessed with 4 antibody IHC (MLH1, PMS2, MSH2, MSH6) and 48% with 2 (PMS2 and MSH6). This included 32 (5%) patients with MLH1 loss and 488 (75%) with PMS2/MLH1 loss (together 80% of MMRd cohort), 1% (n= 9) MSH2, 11% (n=75) MSH6, 4% (n=24) PMS2, and 4% (n=24) with loss of MSH2/MSH6). 76 cases were confirmed to have MLH1 hypermethylation but 67% of cases with loss of MLH1 or PMS2/MLH1 did not have methylation testing performed. The majority MMRd ECs were FIGO stage I (75%) and endometrioid histotype (90%). Patients with loss of MLH1 or PMS2/MLH1 were older (p<0.001), had higher BMI (p<0.001) and had tumors with more LVI (p=0.031), deep myoinvasion (p<0.001) and grade 3 (p=0.046) compared to remainder of MMRd EC. 9% of the MMRd cohort were ER negative, 8% with loss of MLH1 or PMS2/MLH1 and 16% in remainder of MMRd. Inferior outcomes were observed for progression-free survival and overall survival in patients with MLH1 or PMS2/MLH1 loss compared with the remainder of MMRd. ER, L1CAM and CTNNB1 status were not associated with clinical outcomes across the total MMRd cohort, nor within MLH1 or PMS2/MLH1 loss. There was diversity in the immune landscape within MMRd EC with significantly lower CD8 levels in MLH1 or PMS2/MLH1 loss compared to the remainder of MMRd EC. Furthermore, 25% of the MLH1 or PMS2/MLH1 loss group were tumor infiltrating lymphocyte (TIL) ‘low’/immune cold by cluster analysis compared to 11% in the remainder of MMRd EC. Only 16 patients (2.4%) were identified as having LS but 82% of these MMRd patients had not been tested (31% non-LS testing attributable to identification of hypermethylation of MLH1). Conclusion: Substratification within MMRd ECs can provide prognostic and predictive information, with loss of MLH1 and/or its dimer partner PMS2 identifying a subset of MMRd EC with inferior outcomes that may be attributed to lower TIL. ER, L1CAM, and CTNNB1 mutation status do not add prognostic refinement within MMRd EC. Citation Format: Amy Jamieson, Jennifer Pors, Samuel Leung, Derek Chiu, Stefan Kommoss, Aline Talhouk, David G. Huntsman, Naveena Singh, Blake Gilks, Jessica N. McAlpine. Substratification of mismatch repair deficient (MMRd) endometrial cancers can provide prognostic and predictive refinement [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr B026.

A tale of two pathways: Review of immune checkpoint inhibitors in DNA mismatch repair-deficient and microsatellite instability-high endometrial cancers.

The DNA mismatch repair (MMR) pathway is critical for correcting DNA mismatches generated during DNA replication. MMR-deficiency (MMR-D) leads to microsatellite instability (MSI) associated with an increased mutation rate, driving cancer development. This is particularly relevant in endometrial cancer (EC) as 25%-30% of tumors are of MMR-D/MSI-high (MSI-H) phenotype. Comprehensive assessment using immunohistochemistry (IHC) and sequencing-based techniques are necessary to fully evaluate ECs given the importance of molecular subtyping in staging and prognosis. This also influences treatment selection as clinical trials have demonstrated survival benefits for immune checkpoint inhibitors (ICIs) alone and in combination with chemotherapy for MMR-D/MSI-H EC patients in various treatment settings. As a portion of MMR-D/MSI-H ECs are driven by Lynch syndrome, an inherited cancer predisposition syndrome that is also associated with colorectal cancer, this molecular subtype also prompts germline assessment that can affect at-risk family members. Additionally, heterogeneity in the tumor immune microenvironment and tumor mutation burden (TMB) have been described by MMR mechanism, meaning MLH1 promoter hypermethylation versus germline/somatic MMR gene mutation, and this may affect response to ICI therapies. Variations by ancestry in prevalence and mechanism of MMR-D/MSI-H tumors have also been reported and may influence health disparities given observed differences in tumors of Black compared to White patients which may affect ICI eligibility. These observations highlight the need for additional prospective studies to evaluate the nuances regarding MMR-D heterogeneity as well as markers of resistance to inform future trials of combination therapies to further improve outcomes for patients with EC.

Divergent immune microenvironments in two tumor nodules from a patient with mismatch repair-deficient prostate cancer

Patients with prostate cancer (PC) generally do not respond favorably to immune checkpoint inhibitors, which may be due to a low abundance of tumor-infiltrating lymphocytes even when mutational load is high. Here, we identified a patient who presented with high-grade primary prostate cancer with two adjacent tumor nodules. While both nodules were mismatch repair-deficient (MMRd), exhibited pathogenic MSH2 and MSH6 alterations, had a high tumor mutational burden (TMB), and demonstrated high microsatellite instability (MSI), they had markedly distinct immune phenotypes. The first displayed a dense infiltrate of lymphocytes (“hot nodule”), while the second displayed significantly fewer infiltrating lymphocytes (“cold nodule”). Whole-exome DNA analysis found that both nodules shared many identical mutations, indicating that they were derived from a single clone. However, the cold nodule appeared to be sub-clonal relative to the hot nodule, suggesting divergent evolution of the cold nodule from the hot nodule. Whole-transcriptome RNA analysis found that the cold nodule demonstrated lower expression of genes related to antigen presentation (HLA) and, paradoxically, classical tumor immune tolerance markers such as PD-L1 (CD274) and CTLA-4. Immune cell deconvolution suggested that the hot nodule was enriched not only in CD8+ and CD4 + T lymphocytes, but also in M1 macrophages, activated NK cells, and γδ T cells compared to the cold nodule. This case highlights that MMRd/TMB-high PC can evolve to minimize an anti-tumor immune response, and nominates downregulation of antigen presentation machinery (HLA loss) as a potential mechanism of adaptive immune evasion in PC.

AZUR-2, a phase III, open-label, randomized study of perioperative dostarlimab monotherapy vs standard of care in previously untreated patients with T4N0 or stage III dMMR/MSI-H resectable colon cancer.

TPS240 Background: Emerging evidence suggests neoadjuvant therapy may benefit patients (pts) with advanced colon cancer. Neoadjuvant immunotherapy has shown promising efficacy for early-stage mismatch repair deficient (dMMR) colon cancer [1,2]. Evidence from other immunogenic tumors suggests that a perioperative approach with immunotherapy may further improve survival outcomes [3,4]. Dostarlimab (anti-PD-1) has shown a favorable benefit:risk profile in previously untreated dMMR locally advanced rectal cancer [5] and in advanced dMMR/microsatellite instability-high (MSI-H) solid tumors [6]. AZUR-2 (NCT05855200) will evaluate the efficacy and safety of perioperative dostarlimab monotherapy vs standard of care (SOC) in pts with previously untreated T4N0 or Stage III dMMR/MSI-H resectable colon adenocarcinoma. Methods: AZUR-2 is a global, multicenter, randomized, open-label Phase III study. Approximately 711 pts will be enrolled. Key eligibility criteria include age ≥18 years, no prior therapy or surgery for colon cancer, ECOG PS 0–1, and no symptomatic bowel obstruction. Central prescreening is available at sites without local dMMR/MSI-H testing (not required if dMMR/MSI-H already determined). Pts stratified by clinical tumor/node (TN) staging will be randomized 2:1 to receive dostarlimab pre- and post-surgery, or surgery followed by SOC (adjuvant FOLFOX/CAPEOX for 3–6 months or watch and wait approach per physician’s discretion). Primary endpoint is event-free survival (EFS) (events: recurrence based on radiological assessment by blinded independent central review or pathological assessment of new lesions, disease progression precluding surgery, treatment (tx)-related toxicity precluding surgery, or death). Secondary endpoints include pathological response, OS, and safety. Disease assessments will consist of CT scans of chest, abdomen, and pelvis. Pts will undergo safety follow-up at end of tx and at 30 and 90 days after last dose. Efficacy will be assessed in all pts randomized (intent-to-treat) and safety in all pts who receive surgery or ≥1 dose of study tx. A stratified log-rank test will be used for primary analysis. The primary analysis for EFS with >90% power will be conducted after all pts have been followed for ≥3 years. An interim EFS analysis will be conducted ~12 months earlier. Exploratory endpoints include pt-reported outcomes to evaluate health-related quality of life.

Genomic Landscape of Lynch Syndrome Colorectal Neoplasia Identifies Shared Mutated Neoantigens for Immunoprevention

Background & AimsLynch syndrome (LS) carriers develop mismatch repair deficient (MMRd) neoplasia with high neoantigen (neoAg) rates. No detailed information on targetable neoAgs from LS pre-cancers exists, which is crucial for vaccine development and immune-interception strategies. We report a focused somatic mutation and frameshift-neoAg landscape of microsatellite loci from colorectal polyps without malignant potential (PWOMPs), pre-cancers and early-stage cancers in LS carriers. MethodsWe generated paired whole-exome and transcriptomic sequencing data from 8 colorectal PWOMPs, 41 pre-cancers, 8 advanced pre-cancers, and 12 early-stage cancers of 43 LS carriers. A computational pipeline was developed to predict, rank, and prioritize the top 100 detected mutated neoAgs that were validated in vitro using ELISpot and tetramer assays. ResultsMutation calling revealed >10 mut/Mb in 83% of cancers, 63% of advanced pre-cancers, and 20% of pre-cancers. Cancers displayed an average of 616 MHC-I neoAgs/sample, 294 in advanced pre-cancers, and 107 in pre-cancers. No neoAgs were detected in PWOMPs. A total of 65% of our top 100 predicted neoAgs were immunogenic in vitro, and were present in 92% of cancers, 50% of advanced pre-cancers, and 29% of pre-cancers. We observed increased levels of naïve CD8+ and memory CD4+ T-cells in MMRd cancers and pre-cancers via transcriptomics analysis. ConclusionsShared frameshift-neoAgs are generated within unstable microsatellite loci at initial stages of LS carcinogenesis and can induce T-cell responses, generating opportunities for vaccine development, targeting LS pre-cancers and early-stage cancers.

Immunotherapy in mismatch repair-deficient metastatic colorectal cancer – Outcome and novel predictive markers

BackgroundThis study aims to assess predictive markers for response to immunotherapy in dMMR/MSI-H metastatic colorectal cancer (mCRC) patients. Materials and methodsA study using two prospective cohorts from MD Anderson Cancer Center and Sheba Medical Center of consecutive patients with dMMR/MSI-H mCRC that were treated with immunotherapy between 2014–2022. Primary outcome was progression-free survival (PFS) and secondary outcome was overall response rate (ORR). Evaluated predictors included ECOG-PS score, RAS/BRAF status, single-agent versus doublet immunotherapy, metastatic sites, disease burden, and CEA levels prior to treatment initiation. Kaplan-Meier analysis and Cox proportional hazard regression model were used to analyze the effect of exposure variables on PFS. ResultsThe study included 153 patients. Median follow-up time was 26 months (IQR 11–48). Median PFS was 51.6 months (95%CI 38.1-NR) and ORR was 58.1%. In a univariate analysis, male sex was associated with worse PFS with a HR of 1.67 (95% CI 1.00–2.79); Right-sided tumors were associated with improved PFS with a HR of 0.56 (95% CI 0.32–0.97); Liver or lung metastasis were associated with worse PFS with HRs of 2.35 (95%CI 1.43–3.88) and 2.30 (95%CI 1.31–4.04), respectively; ECOG-PS score ≥ 2, CEA levels ˃5 μg/L prior to treatment initiation and ≥ 3 metastatic sites were associated with worse PFS with HRs of 2.09 (95%CI 0.98–4.47), 2.23 (95%CI 1.30–3.81) and 3.11 (95%CI 1.61–6.03), respectively. Liver or lung metastasis remained significant in a multivariable model. ConclusionsExtent of disease (worse PFS with high CEA, poor ECOG-PS and ≥3 metastatic sites) and disease location (worse PFS with liver or lung metastasis and left sided tumor) were associated with immunotherapy outcome in dMMR/MSI-H mCRC.

Immune checkpoint inhibitors with chemotherapy for primary advanced mismatch repair-deficient endometrial cancer: A cost-effectiveness analysis

ObjectiveThe addition of immune checkpoint inhibitors (ICIs), pembrolizumab or dostarlimab, to paclitaxel and carboplatin (TC) has shown better response rates and survival outcomes for patients with primary advanced mismatch repair-deficient (MMRd) endometrial cancer (EC) in NRG-GY018 and RUBY, respectively. Nonetheless, the high cost of ICIs remains a major concern when implementing this strategy in the real world. This study aimed to determine the cost-effectiveness of pembrolizumab and dostarlimab with chemotherapy compared to TC for primary advanced MMRd EC. MethodsWe developed a Markov model including 6600 patients with primary advanced MMRd EC to simulate treatment outcomes. The initial decision points in the model were treatment with pembrolizumab with TC (PEM-TC), dostarlimab with TC (DOS-TC), and TC. Model probabilities, costs, and health utility values were derived with assumptions from published literature. Effectiveness was determined as average quality-adjusted life years (QALYs) gained. The primary outcome was the incremental cost-effectiveness ratio (ICER). ResultsTC was the least costly strategy, whereas PEM-TC was the most effective strategy for primary advanced MMRd EC. TC was cost-effective based on a willingness-to-pay (WTP) threshold of $100,000/QALY compared with PEM-TC (ICER, $377,718/QALY), and DOS-TC exhibited absolute dominance (ICER, $401,859/QALY). PEM-TC was cost-effective when the cost of pembrolizumab 200 mg was reduced to $4361 (61% reduction). PEM-TC was selected in 16.5% with a WTP threshold of $300,000/QALY, but in <1% with a WTP threshold range of $100,000-200,000/QALY. ConclusionPEM-TC can become cost-effective for primary advanced MMRd EC when the cost of pembrolizumab substantially decreases.

DNA mismatch repair deficient cancer - Emerging biomarkers of resistance to immune checkpoint inhibition.

The DNA mismatch repair pathway is involved in the identification, excision, and repair of base-base mismatches and indel loops in the genome. Mismatch repair deficiency occurs in approximately 20% of all cancers and results in a type of DNA damage called microsatellite instability. In 2017, the immune checkpoint inhibitor, Pembrolizumab, an anti-PD-1 therapy, was approved for use in all unresectable or metastatic tumours that were mismatch repair deficient or had high microsatellite instability regardless of tissue origin. This landmark approval was the first time a drug had been approved in a site agnostic way, but accumulating data has revealed that up to 50% of mismatch repair deficient tumours are refractory to treatment and there is a huge amount of variability in the therapeutic benefit amongst responders. Several mechanisms of resistance to immune checkpoint blockade for mismatch repair deficient cancers have been identified but our understanding of what is driving resistance in a proportion of patients remains lacking. In this review article, we discuss the emerging mechanisms of resistance which may enable optimal stratification of patients for treatment with immune checkpoint inhibitors in the future.

LBA7 Pembrolizumab versus chemotherapy in microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): 5-year follow-up of the KEYNOTE-177 study Asia subgroup

LBA7 Pembrolizumab versus chemotherapy in microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): 5-year follow-up of the KEYNOTE-177 study Asia subgroup

Locally advanced mismatch repair-deficient gastroesophageal junction cancer: Diagnosis, treatment modifications, and monitoring.

Locally advanced mismatch repair-deficient gastroesophageal junction cancer: Diagnosis, treatment modifications, and monitoring.

High-plex spatial transcriptomic profiling reveals distinct immune components and the HLA class I/DNMT3A/CD8 modulatory axis in mismatch repair-deficient endometrial cancer.

Tumors bearing mismatch repair deficiency (MMRd) are characterized by a high load of neoantigens and are believed to trigger immunogenic reactions upon immune checkpoint blockade treatment such as anti-PD-1/PD-L1 therapy. However, the mechanisms are still ill-defined, as multiple cancers with MMRd exhibit variable responses to immune checkpoint inhibitors (ICIs). In endometrial cancer (EC), a distinct tumor microenvironment (TME) exists that may correspond to treatment-related efficacies. We aimed to characterize EC patients with aberrant MMR pathways to identify molecular subtypes predisposed to respond to ICI therapies. We applied digital spatial profiling, a high-plex spatial transcriptomic approach covering over 1,800 genes, to obtain a highly resolved TME landscape in 45 MMRd-EC patients. We cross-validated multiple biomarkers identified using immunohistochemistry and multiplexed immunofluorescence using in-study and independent cohorts totaling 123 MMRd-EC patients and validated our findings using external TCGA data from microsatellite instability endometrial cancer (MSI-EC) patients. High-plex spatial profiling identified a 14-gene signature in the MMRd tumor-enriched regions stratifying tumors into "hot", "intermediate" and "cold" groups according to their distinct immune profiles, a finding highly consistent with the corresponding CD8 + T-cell infiltration status. Our validation studies further corroborated an existing coregulatory network involving HLA class I and DNMT3A potentially bridged through dynamic crosstalk incorporating CCL5. Our study confirmed the heterogeneous TME status within MMRd-ECs and showed that these ECs can be stratified based on potential biomarkers such as HLA class I, DNMT3A and CD8 in pathological settings for improved ICI therapeutic efficacy in this subset of patients.

SEAMARK: phase II study of first-line encorafenib and cetuximab plus pembrolizumab for MSI-H/dMMR BRAFV600E-mutant mCRC.

Patients with both BRAF V600E mutations and microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC) have poor prognosis. Currently, there are no specifically targeted first-line treatment options indicated for patients with mCRC whose tumors harbor both molecular aberrations. Pembrolizumab is a checkpoint inhibitor approved for the treatment of MSI-H/dMMR mCRC, and the BRAF inhibitor encorafenib, in combination with cetuximab, is approved for previously treated BRAF V600E-mutant mCRC. Combination of pembrolizumab with encorafenib and cetuximab may synergistically enhance antitumor activity in patients with BRAF V600E-mutant, MSI-H/dMMR mCRC. SEAMARK is a randomized phase II study comparing the efficacy of the combination of pembrolizumab with encorafenib and cetuximab versus pembrolizumab alone in patients with previously untreated BRAF V600E-mutant, MSI-H/dMMR mCRC.

DNA mismatch repair protects the genome from oxygen-induced replicative mutagenesis.

DNA mismatch repair (MMR) corrects mismatched DNA bases arising from multiple sources including polymerase errors and base damage. By detecting spontaneous mutagenesis using whole genome sequencing of cultured MMR deficient human cell lines, we show that a primary role of MMR is the repair of oxygen-induced mismatches. We found an approximately twofold higher mutation rate in MSH6 deficient DLD-1 cells or MHL1 deficient HCT116 cells exposed to atmospheric conditions as opposed to mild hypoxia, which correlated with oxidant levels measured using electron paramagnetic resonance spectroscopy. The oxygen-induced mutations were dominated by T to C base substitutions and single T deletions found primarily on the lagging strand. A broad sequence context preference, dependence on replication timing and a lack of transcriptional strand bias further suggested that oxygen-induced mutations arise from polymerase errors rather than oxidative base damage. We defined separate low and high oxygen-specific MMR deficiency mutation signatures common to the two cell lines and showed that the effect of oxygen is observable in MMR deficient cancer genomes, where it best correlates with the contribution of mutation signature SBS21. Our results imply that MMR corrects oxygen-induced genomic mismatches introduced by a replicative process in proliferating cells.

LBA32 Pembrolizumab versus chemotherapy in microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): 5-year follow-up of the randomized phase III KEYNOTE-177 study

LBA32 Pembrolizumab versus chemotherapy in microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): 5-year follow-up of the randomized phase III KEYNOTE-177 study

628P Immunotherapy in mismatch repair-deficient metastatic colorectal cancer: Long-term outcome and novel predictive markers

628P Immunotherapy in mismatch repair-deficient metastatic colorectal cancer: Long-term outcome and novel predictive markers