MSH2 Mutations Research Articles

DNAR-13. LONG TERM FOLLOW-UP OF A LYNCH SYNDROME-ASSOCIATED GLIOBLASTOMA RESISTANT TO STANDARD-OF-CARE CHEMORADIATION

Abstract BACKGROUND Lynch syndrome is caused by pathogenic germline variants in the DNA mismatch repair (MMR) genes, predisposing individuals to malignancies, including glioblastoma (GBM). MMR-deficient tumors are resistant to monofunctional alkylators such as temozolomide but not to bifunctional alkylators such as the nitrosourea lomustine. Anti-programmed cell death protein 1 (PD1) immune checkpoint inhibitor (ICI) pembrolizumab represents another treatment option, which is approved by the United States Food and Drug Administration (FDA) for the treatment of mismatch repair deficient cancers. METHODS We present a patient with multifocal GBM and Lynch syndrome who experienced rapid progression following standard-of-care chemoradiation, followed by durable responses to lomustine and then to pembrolizumab. RESULTS A 58-year-old man with Lynch syndrome (MSH2 mutation) and prior history of colon cancer presented with seizures. Magnetic resonance imaging (MRI) brain identified right frontal and left parietal masses. Right frontal tumor was resected; pathology was consistent with GBM, IDH wildtype, MGMT-unmethylated. Both lesions were treated with radiation therapy (60 Gy, 30 fractions) with concurrent and adjuvant temozolomide. After two cycles of adjuvant temozolomide, his left parietal tumor progressed and was subtotally resected, followed by four cycles of lomustine (stopped due to myelotoxicity). He remained progression-free for 15 months. Surveillance MRI identified new enhancement involving the left frontal lobe, left periventricular white matter, and right internal auditory canal, concerning for leptomeningeal dissemination. MRI spine identified no additional lesions. Cerebrospinal fluid cytology was negative for tumor cells on two occasions. Patient was treated with pembrolizumab. He remains on treatment with stable disease four months after ICI initiation and 31 months after GBM diagnosis. CONCLUSIONS Patients with MMR-deficient GBM resist standard chemoradiation. Alternatives such as nitrosourea or ICI therapy may achieve durable responses. While data is insufficient to administer these agents as upfront therapy in this specific setting, both should be considered as options for recurrent disease.

Association of multilocus sequence typing, MSH2 gene mutations, and antifungal resistance in Candida glabrata: implications for clinical outcomes in Chinese hospitals

BackgroundCandida glabrata is the second most common cause of invasive candidiasis worldwide. In this study, we determined the clinical characteristics and drug sensitivity of C. glabrata isolates and investigated the associations between MSH2 gene mutations, sequence types (ST), and drug resistance.MethodsA total of 154 C. glabrata isolates were collected from patients being treated in three hospitals in China. The antifungal sensitivity of the strains was assessed using the broth microdilution method. Multilocus sequence typing (MLST) was also performed, followed by MSH2 sequencing. The clinical features and outcomes of C. glabrata infection were analysed for a total of 49 strains, which were collected from patients with invasive Candida infection at Longhua Hospital.ResultsAll 154 isolates were found to be susceptible to amphotericin, 5-fluorocytosine, anidulafungin, caspofungin, and micafungin, whereas 11.7% were fluconazole-resistant, 18.8% were itraconazole non-wild type, and 35.7% were voriconazole non-wild type. ST7 (62.34%) was the most common ST genotype, followed by ST10 (16.88%) and ST15 (7.79%). The total azole resistance rates for all isolates, ST7, ST10, and other STs were 36.4, 42.7, 34.6, and 18.8%, respectively. The ST7 and ST10 isolates were characterised by a higher drug resistance rate than the other minor ST isolates. Moreover, 59.09% of isolates had one or more MSH2 non-synonymous mutations, with V239L being the most commonly detected mutation. The frequency of MSH2 mutations was significantly higher in azole-resistant isolates than in other isolates, whereas P6L or L87P mutations were associated with the highest azole resistance rates of up to 87.5% and 80%, respectively. Our results indicated that ST7 and ST15 are independent predictors of mortality caused by C. glabrata infection and revealed a higher 30-day mortality in patients infected with these strains than in those infected with other ST isolates.ConclusionsOur findings revealed the relationships between MLST, MSH2 gene mutations, and drug resistance in the common pathogenic fungus C. glabrata, and thereby enabled us to identify strains that are associated with higher rates of mortality. These findings will contribute to enhancing our understanding of the pathogenesis of C. glabrata infection.

Biallelic Mismatch Repair Deficiency in Children and Adolescents: A Review of Published and Unpublished Data from India—Need for an Indian Consortium

Abstract Introduction Biallelic mismatch repair deficiency or constitutional mismatch repair deficiency (CMMRD) is a rare and aggressive pediatric cancer predisposition syndrome that occurs as a result of homozygous (biallelic) pathogenic variants in mismatch repair genes. The primary malignancies that occur in CMMRD are mainly hematological and brain malignancies. Most published data are from the western populations and the Middle East. Data from India are limited to case reports. We performed an analysis to determine the prevalence of CMMRD in the Indian population. Materials and Methods All children aged less than 18 years with a diagnosis of CMMRD from various centers in India were included. CMMRD confirmed using genetic, molecular, and clinical criteria by an international consensus was included in the analysis. Literature search and data submitted by individual centers were reviewed. Results The analysis revealed that 22 children had genetically confirmed CMMRD. The median age of the cohort was 6.5 years, with a male predominance (male:female, 2:1). The classical phenotype of café-au-lait macules was observed in 72.7 % of subjects. The most common pathological variant was found in the PMS2 gene, which accounted for 77.3 % of children. Hematological malignancy (T cell acute lymphoblastic leukemia) was the most common primary malignancy in our study that occurred at a median age of 5 years (interquartile range 4–6 years) followed by brain tumors. The age at initial presentation for CMMRD with mutations in MSH2, MSH6, and PMS2 was 5.4, 4, and 7.5 years, respectively. Conclusion The diagnosis of CMMRD requires a high index of suspicion for the early diagnosis, management, surveillance, counseling, and testing of family members. The awareness about CMMRD in clinicians is important so that diagnosis is made early, and a second malignancy is detected and treated early. The need for an Indian consortium to determine the actual burden of the disease, genetic characteristics, and course of illness in our country has been emphasized.

Lynch Syndrome-associated Genomic Variants.

Lynch Syndrome, a hereditary disorder characterized by germline mutations in mismatch repair (MMR) genes, is a major contributor to colorectal cancers. It has also been identified in endometrial cancer. Despite the established role of MMR deficiency in tumorigenesis, the specific genomic alterations driving Lynch syndrome-associated endometrial cancer, and their overlap with colorectal cancer, remain incompletely understood. This study aims to fill this gap by performing a detailed comparative analysis of germline and somatic mutations in endometrial cancer within the context of Lynch syndrome. We conducted whole exome sequencing on matched germline and somatic DNA from 13 patients diagnosed with Lynch syndrome-associated endometrial cancer. High-depth sequencing was performed, followed by rigorous bioinformatics analysis to identify and annotate variants, focusing on their potential pathogenicity and relevance to both endometrial and colorectal cancer. Our analysis revealed 1,118 germline and 14,051 somatic variants, with 493 variants common to both. Recurrent pathogenic mutations in MLH1, MSH2, and MSH6 were confirmed, highlighting their critical role in Lynch syndrome. Notably, frequent somatic mutations in the PIK3CA and PTEN genes were identified, implicating the PI3K/AKT/mTOR pathway as a key oncogenic driver in these cancers. Additionally, novel somatic mutations in genes related to the extracellular matrix such as FBN1 and SPARC were uncovered, suggesting a possible unique role in endometrial tumor progression. This study provides new insights into the molecular basis of Lynch syndrome-associated endometrial cancer, emphasizing the overlap in oncogenic pathways with colorectal cancer. The discovery of shared and unique genetic mutations highlights the importance of developing combined treatment strategies and suggests that targeting these specific mutations could improve therapy for patients with Lynch syndrome-associated cancers.

Double Heterozygosity for Germline Mutations in Chinese Breast Cancer Patients.

Double pathogenic mutations occurring in an individual are considered a rare event. The introduction of a multiple-gene panel at Hong Kong Hereditary Breast Cancer Family Registry has allowed the identification of pathogenic variants in multiple genes, providing more information on clinical management and surveillance to the proband and their family members. Breast cancer patients who are double heterozygous (DH) for different hereditary breast and ovarian cancer syndrome (HBCO)-related genes were identified from a cohort of 3649 Chinese patients. Nine patients (0.25%) were observed to have germline DH mutations in ATM, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, MSH6, PALB2, and TP53. Three probands were diagnosed with unilateral breast cancer, two patients were diagnosed with bilateral breast cancer, and four patients had multiple primary cancers. The median age for breast cancer diagnosis was an early age of 36 years. Chinese DH carriers did not show worse phenotypes or have a significantly downhill clinical presentation. However, seven out of nine (77.8%) of our DH carriers harbored a BRCA1 mutation, and four of them (44.4%) developed bilateral breast cancer, suggesting Chinese DH individuals may have a higher chance of having bilateral breast cancer than other populations (p = 0.0237).

Attenuated adenomatous polyposis with MSH6 variation: Two case reports.

Adenomatous polyposis (AP) is a genetic disorder characterized by the occurrence of numerous adenomatous polyps in the colon and rectum and can be classified into classical AP and attenuated AP (AAP). AAP is diagnosed when the number of observed adenomas is between 10 and 99. The detection of AAP is significantly increasing mainly due to the improvement of the imaging technique and application of the screening program for colorectal cancer detection. Currently, the germline variations of the APC and MUTYH genes are reported as the main cause of classical AP. However, the underlying genetic basis of AAP is not well understood. In this study, we report 2 cases of AAP with MSH6 variations. Both patients visited the hospital after multiple polyps were detected during colonoscopies conducted as part of their health checkups. The 2 patients were diagnosed with AAP through colonoscopic examination at our hospital. The 2 received genetic consultation; and, for follow-up purposes, both patients agreed to be tested for an underlying genetic condition through next generation sequencing. And germline MSH6 variations were detected in both AAP patients. There was no recurrence for both patients for 3 years follow-up. Minor portion of AAP can cause by genetic mutation in MSH6, and further research is needed.

Lynch Syndrome and Thyroid Nodules: A Single Center Experience.

Lynch syndrome (LS) is a genetic disease with increased risk of colorectal cancer and other malignancies. There are few reported cases of thyroid cancer in LS patients. The aim of this study is to investigate the presence of thyroid nodules in LS patients and to explore their association with the genetic features of the disease. A retrospective and descriptive analysis was conducted to include all LS patients followed at the CEMAD (Centro Malattie Apparato Digerente) of Fondazione Policlinico Universitario A. Gemelli IRCCS. The characteristics of LS disease, gene mutations, and previous history of thyroid disease were evaluated. Majority of patients underwent thyroid ultrasound (US), and nodule cytology was performed when needed. Of a total of 139 patients with LS, 110 patients were included in the study. A total of 103 patients (74%) underwent thyroid ultrasound examinations, and 7 patients (5%) had a previous history of thyroid disease (cancer or multinodular goiter). The mean age was 51.9 years. Thyroid nodules were found in 62 patients (60%) who underwent US, and 9 of them (14%) had suspicious features of malignancy, inducing a fine-needle aspiration biopsy. A cytologic analysis classified 7 of 9 cases (78%) as TIR2 and 2 (22%) as TIR3a. Between patients with nodular thyroid disease (single nodule, multinodular goiter, and cancer), most of them (25 patients, 36% of total) were carriers of the MSH6 mutation, while 22 (32%), 17 (24%), and 5 (7%) had MSH2, MLH1, and PMS2 mutations, respectively. A high prevalence of thyroid nodules was found in patients with LS, especially in MSH6-carrying patients. Performing at least one thyroid ultrasound examination is suggested for the detection of nodular thyroid disease in LS patients. Systematic investigations are needed to estimate their prevalence, features, and risk of malignant transformation.

Genomic analysis of recurrent early stage and de novo metastatic colorectal cancer among veterans.

e15593 Background: The Veterans Health Administration (VHA) diagnoses approximately 4,000 cases of colon cancer each year and conducts Next Generation Sequencing (NGS) on recurrent and metastatic cases. The molecular profile of cancers resected for cure that recur is poorly characterized and holds promise to clarify both the risk and mechanisms of recurrence. We sought to characterize these genetic differences. Methods: A national database from the VHA consisting of colon cancer patients was analyzed for those with recurrent disease who have received NGS testing from 2015-2021. Data was analyzed by stage and presence of DNA mismatch repair (MMR) (MLH1, MSH2, PMS2, MSH6) and DNA damage repair (DDR) abnormalities (BRCA1, BRCA2, ATM, BRIP1, BARD1, CDK12, CHEK1, CHEK2, FANCL, PALB2, RAD51B, RAD51C, RAD51D) in addition to receipt of chemotherapy and overall survival with univariate and multivariate cox proportional hazards analyses and multivariate logistic regression analyses. Chi squared analyses were also performed comparing presence of DNA abnormalities between early recurrent and stage IV cancers. Results: From309,318 cases with colon cancer codes, we identified 2,366 colon cancer patients who had NGS and had recurrent or de novo metastatic disease. 1,072 patients had initial staging annotated (I n = 89, II n = 194, III n = 320 , IV n = 453). The average age was 69.41 years; 70.5% white, 21.5% Black and 7.8% other. Among all patients, DNA MMR abnormalities (n = 117) were associated with better overall survival, after controlling for age and race (HR 0.6, 95% CI 0.42-0.85, p < 0.005). Among recurrent early stage (I-III) and stage IV patients, MMR (n = 55 and n = 21, respectively) is associated with improved survival in multivariable models (HR 0.39, 95% CI 0.33-0.46, p < 0.001) . Among the 4 DNA MMR genes, MSH2 mutations had the strongest association with survival (univariate HR 0.31, 0.15-0.62, p < 0.001). Among patients with MMR abnormalities, those who received either only capecitabine or only fluorouracil (without irinotecan or oxaliplatin) had worse overall survival (HR 2.6, 1.34 -5.04, p < 0.005). This effect was more pronounced in early stage recurrent patients versus patients with de novo metastatic disease (HR 5.1, 1.87 – 13.9, p < 0.001). Finally, we also found that early stage patients with recurrent disease are more likely to have MMR abnormalities compared to de novo metastatic (8.8% vs 4.6%, p < 0.01) and confirmed this finding after controlling for race and age. (OR 2.13, p < 0.005). Conclusions: Among Veteranswith colon cancer, resected recurrent colon cancer is more likely to have DNA MMR abnormalities than de novo metastatic disease. Veterans with recurrent and or metastatic disease with DNA MMR have better outcomes regardless of stage at diagnosis. These findings suggest different pathogenesis for those with recurrent disease after curative resection, and for those with de novo metastatic disease.

Deciphering the pancreatic cancer microbiome in Mainland China: Impact of Exiguobacterium/Bacillus ratio on tumor progression and prognostic significance

The existing body of research underscores the critical impact of intratumoral microbiomes on the progression of pancreatic ductal adenocarcinoma (PDAC), particularly in reshaping the tumor microenvironment and influencing gemcitabine resistance. However, peritumoral tissues’ microbiome, distinct from PDAC tumors, remain understudied, and Western-centric analyses overlooking potential variations in dietary-influenced microbiomes. Our study addresses this gap by 16 S rRNA sequencing of PDAC tumors and matched peritumoral tissues from Chinese Mainland patients. Our research has uncovered that the microbiome composition within tumors and paired peritumoral tissues exhibits a high degree of similarity, albeit with certain discrepancies. Notably, Exiguobacterium is found to be more abundant within the tumor tissues. Further investigations have revealed that a lower Exiguobacterium/Bacillus ratio in both the tumor and peritumoral tissues of PDAC patients is indicative of a more favorable prognosis. Further exploration utilizing an orthotopic tumor model demonstrates that the probiotic Bacillus Coagulans impedes PDAC progression, accompanied by an increased infiltration of inflammatory neutrophils in tumors. Additionally, in the subgroup with a low Exiguobacterium/Bacillus ratio, whole-exome sequencing reveals elevated missense mutations in ABL2 and MSH2. The elevated expression of ABL2 and MSH2 has been correlated with poorer prognostic outcomes in PDAC patients. Together, these insights shed light on risk factors influencing PDAC progression and unveil potential therapeutic targets, alongside probiotic intervention strategies.

Mitotic abnormalities precede microsatellite instability in lynch syndrome-associated colorectal tumourigenesis

Lynch syndrome (LS) is one of the most common hereditary cancer syndromes worldwide. Dominantly inherited mutation in one of four DNA mismatch repair genes combined with somatic events leads to mismatch repair deficiency and microsatellite instability (MSI) in tumours. Due to a high lifetime risk of cancer, regular surveillance plays a key role in cancer prevention; yet the observation of frequent interval cancers points to insufficient cancer prevention by colonoscopy-based methods alone. This study aimed to identify precancerous functional changes in colonic mucosa that could facilitate the monitoring and prevention of cancer development in LS. The study material comprised colon biopsy specimens (n=71) collected during colonoscopy examinations from LS carriers (tumour-free, or diagnosed with adenoma, or diagnosed with carcinoma) and a control group, which included sporadic cases without LS or neoplasia. The majority (80%) of LS carriers had an inherited genetic MLH1 mutation. The remaining 20% included MSH2 mutation carriers (13%) and MSH6 mutation carriers (7%). The transcriptomes were first analysed with RNA-sequencing and followed up with Gorilla Ontology analysis and Reactome Knowledgebase and Ingenuity Pathway Analyses to detect functional changes that might be associated with the initiation of the neoplastic process in LS individuals. With pathway and gene ontology analyses combined with measurement of mitotic perimeters from colonic mucosa and tumours, we found an increased tendency to chromosomal instability (CIN), already present in macroscopically normal LS mucosa. Our results suggest that CIN is an earlier aberration than MSI and may be the initial cancer driving aberration, whereas MSI accelerates tumour formation. Furthermore, our results suggest that MLH1 deficiency plays a significant role in the development of CIN. The results validate our previous findings from mice and highlight early mitotic abnormalities as an important contributor and precancerous marker of colorectal tumourigenesis in LS. This work was supported by grants from the Jane and Aatos Erkko Foundation, the Academy of Finland (330606 and 331284), Cancer Foundation Finland sr, and the Sigrid Jusélius Foundation. Open access is funded by Helsinki University Library.

Abstract 2408: Comprehensive genomic profiling of ctDNA reveals distinct genomic signatures and therapeutic implications for immunotherapy response in advanced head and neck cancer

Abstract Background: Head and Neck Cancer (HNC) is highly prevalent malignancy in Southeast Asia. We investigated comprehensive genomic profiling (CGP) of ctDNA, aimed to compare genomic landscapes between responders (R) and non-responders (NR) to immunotherapy among advanced HNC patients. Methods: An observational study, ctDNA was evaluated in 69 advanced HNC patients both at the baseline (BL) and during follow up (FL). OncoIndx® CGP was used to identify patient-specific genomic alterations in the ctDNA cohort. Raw sequence alignment and variant calling were performed using iCare® software. Progression-free survival (PFS) and overall survival (OS) were assessed using Kaplan-Meier statistics. Results: Total 250 mutations, encompassing pathogenic (P), likely pathogenic (LP), and variants of unknown significance (VUS), were identified at BL. In FL samples a slight decrease in the overall number of mutations was observed. Loss-of-function (LOF) KMT2C, MSH6 mutations, and activating HNF1α mutations were consistently present at comparable frequencies in BL and FL samples, exhibiting ubiquity across immunotherapy R and NR populations (F test, P 0.00063, OR 13). The variants did not demonstrate statistically significant association with PFS and OS. Most prevalent variants at follow-up emerged from tumor suppressor genes TP53, BRIP1, STAT5B, NF1, suggesting their potential role as therapy-resistant variants. PFS and OS were notably lower for patients with TP53 + BRCA pathway variants compared to their wild-type counterparts (median PFS TP53 + BRCA pathway mutated 2.7 months vs wt 9.1 months, HR = 4.1; median OS TP53 + BRCA pathway mutated 4.7 months vs 12.8 months for wt, HR 7.7). Similarly STAT5B carriers compared to the wild-type STAT5B-bearing population. Multivariate analysis further confirmed the independent role of TP53 + BRCA pathway and STAT5B variants as determinants for worst outcome (P 0.006, HR2.5). Population with prevalent TP53 and STAT5B LOF variants exhibited a strong negative correlation with the PD-L1 score compared to the population with their wild-type counterparts (P 0.03). Average scores for genome-wide homologous recombination deficiency (HRD), bTMB, and loss of LOH were low at BL and FL and did not correlate with the PD-L1 score. Interestingly, bTMB was low for the cohort, Tumor fraction (TF) emerged as an independent prognosticator for OS and PFS. Conclusions: ctDNA revealed distinct genomic signatures in R and NR populations at BL and FL. Significant prevalence of TP53, BRIP1, STAT5B, and NF1 in the NR population suggest a potential role in conferring immunotherapy resistance. Genomic signatures, TMB and TF impacted survival of immunotherapy responders. Integrating CGP into SOC protocol may help in identifying therapy resistance in advanced HNC patients who did not respond to initial treatment. Citation Format: Atul Bharde, Vanita Noronha, Mrunal Ratnaparkhi, Vijay Patil, Bhagwat Jadhav, Sangeeta Prajapati, Anuradha Choughule, Pratik Chandrani, Sumit Haldar, Fauzul Moubeen, Nandini Menon, Kanchan Hariramani, Madhura Basavalingegowda, Aarthi Ramesh, Jayant Khandare, Pankaj Chaturvedi, Gowhar Shafi, Kumar Prabhash. Comprehensive genomic profiling of ctDNA reveals distinct genomic signatures and therapeutic implications for immunotherapy response in advanced head and neck 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 2408.

Abstract 5615: Functional analysis of variants of uncertain significance in the MSH6 mismatch repair gene

Abstract Lynch syndrome (LS) is a hereditary condition that increases patients’ lifetime risk of cancer, primarily colorectal cancer. LS is caused by germline mutations in mismatch repair (MMR) genes, MLH1, MSH2, MSH6, and PMS2. Identification and classification of these mutations is important in LS diagnosis for guiding treatment plans and preventative care for patients’ and their families. However, the consequences of some variants in these genes are not immediately obvious, granting them classification as variants of uncertain significance (VUS). Laboratory functional analysis to determine whether these variants disrupt MMR function in human cells can provide important evidence for understanding the pathogenicity of VUS and reclassifying them. Half of known variants in the MMR gene MSH6 are VUS and, thus, the goal of my project is to provide evidence for a subset of these variants to help provide evidence for reclassification for these variants. We are calibrating and validating functional assays for MSH6 variants, using known MSH6 pathogenic and benign controls. We will then test MSH6 VUS identified in patients as reported in the InSiGHT database, ClinVar database, and current literature. We are using CRISPR gene editing to recreate these variants in the endogenous MSH6 loci in human embryonic stem cells (hESC). Using these edited hESC lines we are examining the impact of the variants on RNA and protein stability, repair of DNA microsatellites, which is a hallmark of normal MMR function, and induction of the MMR-dependent DNA damage response. With this compilation of data, we will convert the results into a quantitative Odds of Pathogenicity value. This Odds of Pathogenicity score can be used by expert variant interpretation committees to help readily reclassify these variants and provide a clearer diagnosis for these suspected Lynch syndrome patients. Citation Format: Elizabeth Szabo, Emily Blackburn, Alexander Radecki, Abhijit Rath, Christopher Heinen. Functional analysis of variants of uncertain significance in the MSH6 mismatch repair gene [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 5615.

Abstract IA013: Unique metabolic changes in Lynch syndrome-associated endometrial cancer

Abstract Lynch syndrome-associated endometrial cancers (ECs) are defined by germline mutations in DNA mismatch repair genes, including MSH2, MSH6, PMS2, and MLH1. Lynch syndrome (LS) tumors have received increased attention in the therapeutic context as these tumors are microsatellite instable and often reflect increased immune cell infiltration and enhanced response to immunotherapy. However, relatively little attention has been paid to pathogenesis of LS ECs. Women with LS represent an at-risk population who could benefit from cancer interception strategies due to a 60% cumulative lifetime risk of developing EC. We developed a mouse model of MSH2 loss targeted to the uterus to evaluate EC pathogenesis, with the goal of elucidating mechanisms that alter disease penetrance for women with hereditary risk for EC development. Our Progesterone Receptor-Cre Msh2f lox/flox mice (abbreviated Msh2KO) develop ECs that closely mimic human EC. Whole transcriptome profiling of Msh2KO EC and Msh2KO normal endometrium compared to wild-type endometrium identified “Mitochondrial dysfunction” as a significantly altered pathway in Msh2 deficiency, prompting our in-depth evaluation of mitochondrial alterations in Msh2KO mice, MSH2-deficient cell lines, and LS-associated EC patient specimens. We will discuss the impact of MSH2 deficiency across multiple measures of mitochondrial content, integrity, function, and metabolomic analyses in ECs using preclinical models and human tissue studies. Overall, our studies reveal that MSH2-deficient EC is characterized by mitochondrial DNA damage, mitochondrial content reduction, and decreased mitochondrial function. In addition, decreased mitochondrial respiration for energy production facilitates metabolic reprogramming toward glycolysis. We are conducting further studies to define mechanisms underlying mitochondrial defects due to MSH2 loss and opportunities for intervention. Mitochondrial and metabolic aberrations could serve as novel biomarkers for EC development and targets for cancer prevention in women with LS. Citation Format: Melinda S. Yates. Unique metabolic changes in Lynch syndrome-associated endometrial cancer [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 IA013.

Mismatch repair gene MSH6 correlates with the prognosis, immune status and immune checkpoint inhibitors response of endometrial cancer.

Many patients treated with immune checkpoint inhibitors (ICIs) developed primary or secondary drug resistance for unknown reasons. This study investigates whether mismatch repair (MMR) genes are responsible for this therapeutic restriction. We obtained the transcriptional, clinical and single nucleotide polymorphism data for endometrial cancer (EC) from The Cancer Genome Atlas and the immunophenoscore data of EC from The Cancer Immunome Atlas, then analyzed in R to evaluate the relationship between MMR genes and clinicopathological features, prognosis, immune infiltration, immune checkpoint expression and responsiveness to ICIs in EC. We used differentially expressed genes in the MSH6 high and low expression groups to conduct GO and KEGG analyses to explore the impact of MSH6 on the biological functions of EC. Finally, we verified the bioinformatics results with in vitro experiments. Our analyses showed that compared with the high MSH6 expression group, the low MSH6 expression group had better survival outcomes and less aggressive clinicopathological features. In the multivariate Cox analysis, MSH6 was the only independent risk factor that could predict the prognosis of EC. Besides, the low MSH6 expression group also had a higher immune score, more active immune infiltration and higher immune checkpoint expression, resulting in better responsiveness to ICIs treatment, consistent with the enrichment of GO terms and KEGG pathways related to immune response in this group. Meanwhile, the GO and KEGG enrichment results of the MSH6 high expression group were associated with cell cycle, DNA damage repair and tumorigenesis. To exclude the influence of MSH6 mutations, we performed the previous analyses on the MSH6 wild-type tumor samples and obtained consistent results. In vitro experiments also confirmed that after knocking down MSH6 in endometrial cancer cells, their proliferation, migration and invasion abilities were weakened, while the expression levels of PD-L1 and PD-L2 were elevated. In comparison, overexpression of MSH6 showed an opposite trend. Reduced MSH6 expression could serve as a potential biomarker for predicting better prognosis, active immune status, higher immune checkpoint expression level and better responsiveness to ICIs treatment in EC. MSH6 may become a potential target for treating solid tumors.

Molecular and clinical characteristics of POLE/POLD1 alterations among patients with colorectal cancer.

184 Background: POLE and POLD1 alterations (DNA polymerase ε and DNA polymerase δ) are key biomarkers of immune response for patients with MSS colorectal cancers (CRC). The clinical and molecular characteristics of POLE/POLD1 alterations are not yet well defined across CRCs. In this study, we investigated the clinical/molecular features of POLE and POLD1 alterations and its association with MSI-H CRC. Methods: All the patients and mutation data were selected from the cBioPortal database (https://www.cbioportal.org). All nonsynonymous mutations including missense, frameshift, nonsense, nonstop, splice site, and translation start site changes of POLE/POLD1 were considered. 21 studies were used in the analysis. 7179 data samples were obtained from 7179 patients. Tumors included were from all stages of CRCs. POLE/POLD1 mutations were from mutation tables, only protein-changing mutations were kept. MSI-H status was based on mutation data (presence of MLH1/PMS2/MSH2/MSH6 mutations). Results: Of 7179 patients with all stage CRCs, 6.1% (439) were found to harbor mutated POLE/POLD1 genes. Among those, 3446 patients had known MSI status and 14.9% (514/3446) had MSI-H disease. Notably, 3.3% patients with POLE/POLD1 mutations were found to have concurrent MSI-H disease (co-existence) and only 1.1% of patients with POLE/POLD1 mutations had MSS CRC. MSI status was unknown for 1.7% of patients with POLE/POLD mutant CRC. The mean age for patients with POLE/POLD1 + with or without MSI-H disease was 67. POLE/POLD mutations were exceedingly more common in colon than rectum regardless of MSI-H status (85% vs 15% overall and 88% vs 12% in MSI-H subgroup). No difference was seen among genders for the distribution of POLE/POLD1 mutations. Conclusions: POLE/POLD1 mutations frequently co-exist with MSI-H disease in CRC. Patients with MSS-CRC harboring POLE/POLD1 mutations represent a smaller subgroup of CRC (~1%). The incidence of POLE/POLD1 somatic mutations was more common among patients with colon cancer than those with rectal cancer.

Liquid biopsy-based comprehensive genomic profiling to reveal mutational landscape in real-world patients with gastrointestinal cancer.

735 Background: Molecular characteristics hold substantial clinical significance in cancer. Previous research has elucidated the molecular classification of gastrointestinal (GI) cancers, leveraging biomarkers like gene alterations, MSI, EBV status, and chromosomal instability. However, most of these studies relied on tissue biopsies. Limited investigations have been documented regarding the characterization of molecular profiles through liquid biopsy. Here we present a comprehensive genomic profiling study conducted on advanced GI cancer patients using blood samples. Methods: This prospective study is a part of a global initiative focused on molecular biomarker screening across various solid tumors. Here we report the early result of 106 unresectable GI cancer patients, encompassing those with advanced disease or experiencing relapse after prior treatments. The cohort comprises 66 colorectal cancer (CRC) patients, 34 gastric cancer (GC) patients, and 6 esophageal cancer (EC) patients. Each patient contributed a 10-mL blood sample for comprehensive circulating tumor DNA (ctDNA) analysis. The study employed PredicineCARE, a 152-gene, NGS-based liquid biopsy assay, to profile somatic gene variations within this patient population. Results: The study revealed a total of 1,597 somatic mutations, with 1,077 occurring in CRC, 448 in GC, and 72 in EC. Additionally, 722 gene copy number variants were identified, with 288 in CRC, 351 in GC, and 83 in EC patients. In CRC, the most frequently altered genes (prevalence > 20%) included TP53 (58%), APC (45%), KRAS (33%), and BRCA2 (22%). Conversely, in GC, the most altered genes were TP53 (59%), TERT (35%), FAT1 (29%), ARID1A (26%), and FGFR4 (24%). Among the 6 EC patients, 3 carried TP53 variations, with variations in APC (N=2), ERCC5 (N=2), FAT1 (N=2), and EGFR (N=1) also observed. The mutation burden in CRC (median 3.73 mut/Mb) and GC (median 3.57 mut/Mb) displayed no significant differences. However, the mutation burden in CRC was significantly higher than that in EC (2.24 mut/Mb) (p=0.04). A similar pattern was observed between GC and EC but did not reach statistical significance (p=0.10) due to limitations in cohort size. Furthermore, the assay identified patients carrying both germline and somatic mutations related to homologous recombination deficiency (HRD). In CRC patients, 5 had MLH1 germline mutations, 6 had MSH2 mutations (5 were germline), 4 had MSH6 germline mutations, 2 had PMS2 somatic mutations, and 1 had an EPCAM germline mutation. While in GC patients, 2 had MLH1 germline mutations, 1 had an MSH6 mutation, and 1 had a PMS2 somatic mutation. Conclusions: This study elucidated the comprehensive mutational landscape of advanced gastrointestinal cancer through liquid biopsy, thereby contributing novel biomarkers for clinical diagnosis and facilitating targeted therapy mechanism investigations.

Germline mutations in pediatric cancer cohort with mixed-ancestry Mexicans.

Childhood cancer is one of the primary causes of disease-related death in 5- to 14-year-old children and currently no prevention strategies exist to reduce the incidence of this disease. Childhood cancer has a larger hereditary component compared with cancer in adults. Few genetic studies have been conducted on children with cancer. Additionally, Latin American populations are underrepresented in genomic studies compared with other populations. Therefore, the aim of this study is to analyze germline mutations in a group of mixed-ancestry Mexican pediatric patients with solid and hematological cancers. We analyzed genetic variants from 40 Mexican childhood cancer patients and their relatives. DNA from saliva or blood samples was used for whole-exome sequencing. All variants were identified following GATK best practices. We found that six patients (15%) were carriers of germline mutations in CDKN2A, CHEK2, DICER1, FANCA, MSH6, MUTYH, NF1, and SBDS cancer predisposition genes, and additional new variants predicted to be deleterious by in silico algorithms. A population genetics analysis detected five components consistent with the demographic models assumed for modern mixed-ancestry Mexicans. This report identifies potential genetic risk factors and provides a better understanding of the underlying mechanisms of childhood cancer in this population.

Abstract C086: NP1867, a potent, selective, covalent small molecule inhibitor of DNA Mismatch Repair (MMR) protein PMS2, functionally inhibits MMR in cells and elicits COSMIC mutational signatures consistent with MMR-deficient patient samples

Abstract Two complementary mechanisms safeguard genome fidelity during DNA replication: DNA polymerase proofreading and DNA mismatch repair (MMR). DNA polymerase proofreading or MMR deficiencies can occur independently or, more rarely, simultaneously; loss of function of either or both pathways leads to the accumulation of DNA mutations. Lynch Syndrome is caused by mono-allelic germline mutations in MMR genes MLH1, MSH2, MSH6 or PMS2. Gene expression from the wild-type allele elicits sufficient MMR activity until a second hit somatic mutation inactivates the wild-type allele leading to MMR deficiency (MMR-d). Constitutional mismatch repair deficiency (CMMRD) syndrome is an inherited early onset cancer predisposition syndrome resulting from biallelic germline mutations in MLH1, MSH2, MSH6 or PMS2. MMR-d cancers are commonly and typically characterized by accumulation of single nucleotide variants (SNVs) and insertions or deletions (indels) amongst repetitive DNA sequences - microsatellite instability (MSI); importantly, such mutations occur at higher rates in genetically unstable tumour cells under replicative stress than in normal cells. Cancers that harbour >40% microsatellite variations (positive for two or more of five clinically tested microsatellite markers) are described as MSI-high (MSI-H). Importantly, MMR-d, MSI-H tumours are now eligible for immune checkpoint therapy, irrespective of tissue type, providing substantial patient benefit and a major advance in cancer treatment. This clinical context is consistent with the hypothesis that MMR-d elicits an immunogenic state. However, there is an unmet need for chemical tools to explore the role of therapeutic MMR inhibition alongside immune checkpoint blockade. Here, for the first time, we demonstrate that NP1867 is a potent, selective small molecule inhibitor of the Gyrase, Hsp90, Histidine Kinase, MutL (GHKL) family endonuclease PMS1 Homolog 2, Mismatch Repair System Component (PMS2). We demonstrate by biochemical, biophysical, and protein-ligand X-ray crystallographic methods that NP1867 binds irreversibly to the ATP binding site of the N-terminal ATPase domain of PMS2. NP1867 displays potent binding to PMS2 in a NanoBRET cellular target engagement assay and inhibits MMR activity in cell-based assays of MMR-dependent DNA repair. NP1867 displays minimal off-target binding in broad biochemical screening panels including kinases and ATPases. Treatment of MMR-proficient, colorectal cancer cell lines with NP1867 increases tumour mutational burden and generates COSMIC mutational signatures consistent with MMR-d patient samples demonstrating, for the first time, that acute inhibition of PMS2 with a small molecule phenocopies the epigenetic silencing and/or genetic loss of MMR observed in patients. We characterise cell- and tissue-based target engagement, and in vivo pharmacokinetic and pharmacodynamic properties of NP1867 to inform optimal use by the research community for further exploring PMS2 and MMR function. Citation Format: Julian Blagg, Philippe Riou, Alexia Hervieu, Eleonora Piumatti, Giuseppe Rospo, Sasi Arunachalam, Bettina Meier, Sam Weeks, Maria Rodriguez, Kalpesh Parmar, Pradip Patel, Adam Peall, Paige Tongue, Tess McLaren, Robert Workman, Ruzica Bago, Stuart Robjohns, Rebecca Beaumont, Mike Briggs, Gareth Langley, Charles Nichols, David Clark, Paul Winship, Benoit Rousseau, Matthew Baker, Martin Drysdale, Giovanni Germano, Alberto Bardelli. NP1867, a potent, selective, covalent small molecule inhibitor of DNA Mismatch Repair (MMR) protein PMS2, functionally inhibits MMR in cells and elicits COSMIC mutational signatures consistent with MMR-deficient patient samples [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C086.

Abstract A001: Reshaping the immune microenvironment after temozolomide priming in metastatic colorectal cancer patients in ARETHUSA clinical trial

Abstract Mismatch repair (MMR) proficient (MMRp) tumors, known for their weak immune response, often exhibit limited effectiveness in immunotherapy. In contrast, responsive mismatch repair deficient (MMRd) tumors, characterized by heightened immune activity, show a stronger response to immune checkpoint blockade (ICB). In the ARETHUSA clinical trial (NCT03519412), we revealed that treatment with temozolomide (TMZ) can pharmacologically deactivate the MMR machinery, as indicated by mutational signature analysis and the emergence of MMR gene mutations. We focused our investigation on a subset of initially MMRp CRC patients who experienced sustained disease stabilization with ICB after receiving TMZ priming treatment. This treatment resulted in the emergence of an inactivating MSH6 mutation and the TMZ mutational signature. Additionally, TMZ treatment induced diverse genomic changes, leading to the identification of three distinct subtypes through analysis of blood and tissue samples. Notably, we observed a dose-dependent accumulation of mutations with a specific molecular signature visible at the clonal level (subtype B2) in 10% of patients, at the subclonal level (subtype B1) in 71% of patients, and the absence of these mutations (subtype A) in 19% of patients within our cohort of 21 patients. In conjunction with previous genetic findings, in this new study we performed an analysis of T-cell receptors (TCRs) in the tumor microenvironment following TMZ treatment. Our results revealed expanded clonotypes in tumors that exhibited a clonal increase in mutations following priming treatment. Furthermore, the diversity of TCRs within the immune infiltrate confirmed the categorization of tumors into three distinct classes based on Tumor Mutational Burden (TMB) and mutational signatures. We also established a significant linear correlation (p-value 0.0048) between the diversity of T-cells in the microenvironment and the number of mutations induced by TMZ. Based on these clinically-oriented preliminary findings, we propose that increasing the number of TMZ-induced mutations could enhance the likelihood of TMZ-driven neoantigens triggering clonal expansion of specific T-cell clonotypes within the tumor. Interestingly, the subset of TMZ-treated tumors displaying an acquired MSH6 mutation, TMZ mutational signature, and increased TMB not only achieved temporary disease stabilization with ICB but also exhibited clonal expansion of T-cells in the tumor microenvironment. These clinically relevant findings suggest that the inactivation of MMR achieved through TMZ priming has the potential to reshape the immune microenvironment modulating the immune response in metastatic colorectal cancer. Citation Format: Giovanni Crisafulli, Andrea Sartore-Bianchi, Luca Lazzari, Filippo Pietrantonio, Paolo Battuello, Alice Bartolini, Federica Di Nicolantonio, Silvia Marsoni, Salvatore Siena, Alberto Bardelli. Reshaping the immune microenvironment after temozolomide priming in metastatic colorectal cancer patients in ARETHUSA clinical trial [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr A001.

Prostate cancer patient stratification by molecular signatures in the Veterans Precision Oncology Data Commons.

Veterans are at an increased risk for prostate cancer, a disease with extraordinary clinical and molecular heterogeneity, compared with the general population. However, little is known about the underlying molecular heterogeneity within the veteran population and its impact on patient management and treatment. Using clinical and targeted tumor sequencing data from the National Veterans Affairs health system, we conducted a retrospective cohort study on 45 patients with advanced prostate cancer in the Veterans Precision Oncology Data Commons (VPODC), most of whom were metastatic castration-resistant. We characterized the mutational burden in this cohort and conducted unsupervised clustering analysis to stratify patients by molecular alterations. Veterans with prostate cancer exhibited a mutational landscape broadly similar to prior studies, including KMT2A and NOTCH1 mutations associated with neuroendocrine prostate cancer phenotype, previously reported to be enriched in veterans. We also identified several potential novel mutations in PTEN, MSH6, VHL, SMO, and ABL1 Hierarchical clustering analysis revealed two subgroups containing therapeutically targetable molecular features with novel mutational signatures distinct from those reported in the Catalogue of Somatic Mutations in Cancer database. The clustering approach presented in this study can potentially be used to clinically stratify patients based on their distinct mutational profiles and identify actionable somatic mutations for precision oncology.