MLH1 Research Articles

DMMR/MSI tumour occurrence during follow-up of patients with Lynch syndrome treated with immune checkpoint inhibitors for a metastatic digestive cancer between 2015 and 2024: A retrospective monocentric cohort.

96 Background: Immune check point inhibitor(s) (ICIs) transformed the prognosis of patients with metastatic dMMR/MSI cancers especially for patients with Lynch syndrome (LS). The aim of our study was to describe a population of LS carrier patients treated with ICI(s) for metastatic digestive cancer, specifically assessing the risk of developing metachronous cancer. Methods: We collected data of 93 patients with LS, treated by ICI(s) for a metastatic digestive tumour. These patients were selected from the “immunoMSI” patient cohort, which included all patients presenting with a MSI and/or dMMR digestive cancer treated with ICI(s) between February 2015 and April 2024 in the medical oncology department of Saint-Antoine Hospital (Paris, France). Our primary outcome was the cumulative risk of metachronous MSI/dMMR cancer; secondary outcomes included cumulative risk and time to de novo colorectal polyps, as well as PFS and OS under ICI(s). We performed a cox model to assess the association of predefined variables with OS and PFS under ICI(s). Results: Patients most frequently carried a germline pathogenic variant on the MSH2 (or EPCAM ) gene (47%) or on the MLH1 gene (30%). The majority presented with colorectal cancer (CRC) as their primary cancer (83%), followed by small intestine tumours (6%), stomach and pancreatic cancers (4%) and bile duct cancer (1%). Median age at cancer index was 62 years-old (26-77). A total of 12 out of 93 patients presented metachronous cancers during or after treatment with ICI(s). Ten of these metachronous cancers were dMMR or within the LS spectrum (urothelial n=4, CRC n=2, bilio-pancreatic n=1 and 3 skin cancers including 2 kerato-acanthomas). All patients who developed a metachronous cancer had a complete or partial response under ICI(s) for the index cancer. During a median follow-up of 47.8 months, 44 patients had colonoscopies and a total of 17 patients (39,5 %) developed pre neoplastic colorectal polyps. In multivariate analysis, PS ≥ 2 and age ≥ 70 years were associated with poorer OS with HRs of 6.3 (95% CI [1.5-25.9], p=0.01) and 5.5 (95% CI [1.6-18.9], p=0.006) respectively. Conclusions: Our results show that ICI(s) for patients with LS treated for an MSI/dMMR metastatic digestive cancer can still develop metachronous cancers and pre neoplastic polyps, which underlines the importance of maintaining dedicated follow-up after ICI(s) treatment in this population.

MLH1 gene promoter methylation status partially overlaps with CpG methylator phenotype (CIMP) in colorectal adenocarcinoma.

RAS/BRAF mutations, mismatch DNA repair complex deficiency (MMRd)/microsatellite instability (MSI), and CpG methylator phenotype (CIMP) are key molecular actors in colorectal carcinogenesis. To date, conflicting evidence about the correlations between these molecular features has been reported. A retrospectively selected cohort of 123 CRCs was divided into 3 groups based on the molecular characteristics: MMR proficient (MMRp)/BRAF p.V600E mutated (BRAFmut), MMRd/BRAFmut, and MMRd/BRAF wild type (BRAFwt). MLH1 promoter (pMLH1) methylation status was assessed by pyrosequencing. For 82 samples the CIMP phenotype was evaluated using the EpiTect® MethyLight kit. The MMRd/BRAFmut group showed a higher pMLH1 methylation rate compared to both the MMRd/BRAFwt and the MMRp/BRAFmut groups. Overall, the two MMRd groups had a higher methylation rate compared to the MMRp cases independently from the mutational status of BRAF (p-value <0.0001). The MMRd/BRAFmut group was characterized by a 90.0 % of CIMP high (CIMP-H) tumors of which 97.2 % were pMLH1 methylated. Instead, the MMRd/BRAFwt group presented 50.0 % of CIMP-H adenocarcinomas. Our study demonstrates that pMLH1 hypermethylation, MMRd, BRAFmut and CIMP phenotype do not completely overlap in CRC. These findings further refine the knowledge on the molecular landscape of CRC and may have critical implications also for the clinical management of the disease.

Case report: Chemotherapy plus sintilimab for the treatment of gastroesophageal junction hepatoid adenocarcinoma with liver metastasis: a case study with literature review

ObjectiveTo elucidate the clinicopathological features and treatment of metastatic gastroesophageal junction hepatoid adenocarcinoma (GEJ HAC)using a case study and literature review.MethodsClinical presentation, results of histology and immunohistochemistry, and next-generation sequencing(NGS) in a patient with GEJ HAC metastasizing to the liver were reviewed. Chemotherapy (SOX or S-1) plus sintilimab was administered.ResultsA 65-year-old male patient with a history of hypertension was admitted to the hospital due to a one-week increase in serum AFP levels. There was a small intraluminal mass at the GEJ and a metastatic lesion in liver segment VIII, as well as enlarged perigastric and retroperitoneal lymph nodes. Tumor cells in both the GEJ and liver tissue exhibited a glandular shape with a nest-like adenoid structure. Immunohistochemical (IHC) analysis of the GEJ tissue showed positivity for AFP, CA19-9, CK7, CK20, MUC-1, P53 (wild type), Glypican-3, and HepPar-1, and negativity for Arginase-1, CD10, and Her-2. In the metastatic liver tissue, IHC testing demonstrated positivity for AFP, CD10, CK19, CK20, HepPar-1, MUC-1, Ki-67, and P53 (wild type), while CK7 was negative. The NGS report of GEJ mass indicated that the JAK2 and TP53 genes harbored missense mutations, while the MLH1, MSH2, MSH6, PMS2, ERBB2, EGFR, PIK3CA, APC, CTNNB1, CDH1, and DPYD genes were normal. The patient’s serum levels of CEA, CA19-9, and AFP were sharply decreased. The patient achieved a major pathological response (MPR) and remains in a progression-free stage.ConclusionsSintilimab-based chemotherapy has proven efficacy in achieving a MPR and maintaining a progression-free state for a patient with GEJ HAC that has metastasized to the liver.

MLH1 promoter hypermethylation and Lynch Syndrome: When to test for constitutional epimutations of MLH1 gene?

Lynch syndrome is a genetic condition predisposing to cancer, particularly colorectal cancer and endometrial cancer, due to germline mutations in MisMatch Repair genes. More rarely, Lynch syndrome is the result of a constitutional MLH1 promoter methylation. This review summarizes the current knowledge about the role of this epigenetic mechanism in the Lynch syndrome. Universal Tumor Screening, performed on tumoral specimens to identify features suggestive of Lynch syndrome, shows the same features both in the case of sporadic cancers and Lynch syndrome-cancers due to a constitutional MLH1 methylation: microsatellite instability, deficiency of MisMatch Repair proteins, and methylation of MLH1 gene. Over the last few years, identifying methylation of MLH1 promoter on tumors was used to discern sporadic tumors from Lynch syndrome tumors: the methylation of the MLH1 promoter was usually explained as a somatic event and this could lead to a missed diagnosis of some Lynch syndrome cases. Therefore, establishing criteria to decide when to test patients for constitutional MLH1 methylation is urgent. In the case of microsatellite instability/deficiency of MisMatch Repair tumors with MLH1 methylation, a germline genetic test could be requested for all colorectal cancer patients aged 55 years or younger and all endometrial cancer patients younger than 50 years old, independently from family history. The prevalence of germline MLH1 epimutations is not precisely known and possibly underestimated. The associated cancer risk could be similar to that due to a MLH1 sequence variant. MLH1 epimutations could be secondary to other genetic defects and follow an autosomal dominant inheritance. On the contrary, primary epimutations are often "de novo" events, and their transmission does not follow Mendelian rules.

Genome-Wide Screening in Haploid Stem Cells Reveals Synthetic Lethality Targeting MLH1 and TP53 Deficient Tumours.

Synthetic lethality is defined as a type of genetic interaction where the combination of two genetic events results in cell death, whereas each of them separately does not. Synthetic lethality can be a useful tool in personalised oncology. MLH1 is a cancer-related gene that has a central role in DNA mismatch-repair and TP53 is the most frequently mutated gene in cancer. To identify genetic events that can lead to tumour death once either MLH1 or TP53 is mutated, a genome-wide genetic screening was performed. Thus, mutations in all protein-coding genes were introduced into haploid human embryonic stem cells (hESCs) with and without loss-of-function mutations in the MLH1 or TP53 genes. These experiments uncovered a list of putative hits with EXO1, NR5A2, and PLK2 genes for MLH1, and MYH10 gene for TP53 emerging as the most promising candidates. Synthetic lethal interactions of these genes were validated genetically or chemically using small molecules that inhibit these genes. The specific effects of SR1848, which inhibits NR5A2, ON1231320 or BI2536, which inhibits PLK2, and blebbistatin, which inhibits MYH10, were further validated in cancer cell lines. Finally, animal studies with CCL xenografts showed the selective effect of the small molecule BI2536 on MLH1-null tumours and of blebbistatin on TP53-mutated tumours. Thus, demonstrating their potential for personalised medicine, and the robustness of genetic screening in haploid hESCs in the context of cancer therapeutics.

A Novel Case of Biallelic MLH3 Variants in a Patient With Rectal Cancer and Polyps.

An increasing number of autosomal recessive forms of adenomatous polyposis have been described, but some in very few cases. Here, we describe a rare case of biallelic germline pathogenic variants in the MLH3 gene, implicating it as a potential cause of early colorectal cancer. The patient, a 47-year-old woman, presented with rectal bleeding, leading to the discovery of a malignant rectal tumor and adenomas during colonoscopy. Histopathological examination confirmed adenocarcinoma without microsatellite instability, and genetic testing identified two likely pathogenic frameshift variants in MLH3 located in trans. These findings contribute to the expanding knowledge of MLH3-related polyposis and colorectal cancer and underscore the need for further research into the gene's broader implications, including its potential role in cancer and infertility pathways.

Genomic Medicine in the Developing World: Cancer Spectrum, Cumulative Risk and Survival Outcomes for Lynch Syndrome Variant Heterozygotes with Germline Pathogenic Variants in the MLH1 and MSH2 Genes.

Background: Although genetic testing has improved our ability to diagnose Lynch syndrome (LS), there is still limited information on the extent of variations in the clinical and genetic landscape among LS variant heterozygotes (LSVH) in Africa. We sought to investigate the cancer spectrum, cumulative risk, and survival outcomes of LSVH with pathogenic/likely pathogenic variants (P/LPVs) in the MLH1 and MSH2 genes using a LS registry in South Africa over the last 30 years. Methods: A retrospective study was conducted to retrieve demographic, clinical, and genetic data of all LSVH with P/LPVs in the MLH1 and MSH2 genes from our LS registry. Genetic data were analyzed according to cancer spectrum, cumulative risk, and crude survival. We used the Chi-squared and t-test to assess differences between groups, and Kaplan-Meier survival analyses were used to analyze the cumulative risk and crude survival outcomes. A p-value < 0.05 at a 95% confidence interval was considered statistically significant. Results: We analyzed a total of 577 LSVH from 109 families. About 450 (78%) and 127 (22%) LSVH harbored a disease-causing mutation in MLH1 and MSH2, respectively. A South African founder PV (MLH1:c.1528C>T) accounted for 74% (n = 426) of all LSVH. CRC was the most common diagnosed cancer in both MLH1 and MSH2 LSVH. MLH1 LSVH had a younger age at cancer diagnosis than MSH2 LSVH (43 vs. 47 years, respectively, p = 0.015). Extracolonic cancers were predominantly higher in female LSVH (n = 33, 35%) than in male LSVH (n = 8, 7%) with the MLH1:c.1528C>T founder PV. The cumulative risk of any cancer and CRC at any age was higher in MLH1 LSVH than in MSH2 LSVH (p = 0.020 and p = 0.036, respectively). LSVH with the MLH1:c.1528C>T PV had a better 10-year overall survival after the first cancer diagnosis, particularly for CRC. Conclusions: LSVH with P/LPVs in the MLH1 and MSH2 genes exhibited significant gene- and sex-specific differences in cancer spectrum, cumulative risk and survival outcomes. Cancer risk and survival estimates described in this study can be used to guide surveillance and genetic counselling for LSVH in our population.

Haplotype analysis detects MLH1 founder variant in Indian Lynch syndrome patient cohort.

Lynch syndrome (LS) is an autosomal dominant hereditary cancer predisposition syndrome whereby the lifetime risk of developing gastrointestinal and genitourinary cancers rises by to over 50%. It is caused by heterozygous variants in the DNA mismatch repair genes- MLH1, MSH2, MSH6 and PMS2, with the majority detected in MLH1 and MSH2. Recurrently observed LS-associated variants in apparently unrelated individuals have either arisen de novo in different families due to mutation hotspots or are inherited from a common ancestor (founder) that lived several generations back. Testing for founder variants can facilitate molecular diagnosis of LS more efficiently and cost effectively than screening for all possible variants in the MMR genes. Here, we report a study of the missense variant c.306G > T in the MLH1 gene, the first potential founder variant identified in LS patients of Indian ethnicity. Haplotype analysis consisting of 25 LS carriers with the MLH1 c.306G > T variant and 100 healthy controls confirmed a shared haplotype in cases spanning a 27.8kb region encompassing the c.306G > T variant (𝝌2 = 96.418; p = < 0.0001). Age of variant analysis suggests the variant to have arisen in the population approximately 800 years (95% CI: 670-934 years) ago. Furthermore, it is estimated that c.306G > T variant is likely to be observed in 6.4% of all LS patients of Indian ethnicity. These findings have important implications for genetic counselling and molecular diagnosis of Lynch syndrome.

Genomic mosaicism in colorectal cancer and polyposis syndromes: a systematic review and meta-analysis

BackgroundColorectal cancer (CRC) and polypoid syndromes are significant public health concerns, with somatic mosaicism playing a crucial role in their genetic diversity. This study aimed to investigate the prevalence and impact of somatic mosaicism in these conditions.MethodsA search was conducted using PubMed, Scopus, and Web of Sciences to identify studies evaluating mosaicism in patients with CRC or polyposis syndromes. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to determine prevalence rates. Statistical analyses were performed using R software 4.3.ResultsA total of 27 studies, encompassing 2272 patients, were included in the analysis. Of these, 108 patients exhibited somatic mosaicism, resulting in an overall prevalence of 8.79% (95% CI 5.1 to 14.70%, I2 = 85; p < 0.01). Subgroup analyses revealed a significantly higher prevalence of mosaicism in patients with APC mutations (OR 13.43%, 95% CI 6.36 to 26.18%, I2 = 87; p < 0.01). Additionally, mosaicism in MLH1 and MSH2 genes was observed at rates of 2.75% (95% CI 1.20 to 6.18%) and 9.69% (95% CI 2.98 to 27.24%), respectively.ConclusionsOur findings support the growing recognition of mosaicism as a critical factor in CRC susceptibility and underscore the importance of incorporating mosaicism screening into routine genetic testing for at-risk patients.

Mutations in the PIK3C2B, ERBB3, KIT, and MLH1 Genes and Their Relationship with Resistance to Temozolomide in Patients with High-Grade Gliomas.

The treatment for patients with high-grade gliomas includes surgical resection of tumor, radiotherapy, and temozolomide chemotherapy. However, some patients do not respond to temozolomide due to a methylation reversal mechanism by the enzyme O6-methylguanine-DNA-methyltransferase (MGMT). In patients receiving treatment with temozolomide, this biomarker has been used as a prognostic factor. However, not all patients respond in the same way, which suggests the existence of other proteins involved in resistance to temozolomide chemotherapy. A group of thirty-one patients was recruited who were clinically and pathologically diagnosed with high-grade gliomas. The sequencing of 324 genes related to different types of cancer was performed to detect mutations. Subsequently, a statistical analysis was conducted to determine the mutated genes that were most related to resistance to treatment. According to the Stupp protocol and metronomic dose of the temozolomide treatment, the mutated genes related to the second relapse of patients with high-grade glioma were PIK3C2B, KIT, ERBB3, and MLH1. Considering the results obtained, we suggest that mutations in the four genes and methylation of the gene promoter that codes for the MGMT protein could be related to response to treatment with temozolomide.

In silico splicing analysis of the PMS2 gene: exploring alternative molecular mechanisms in PMS2-associated Lynch syndrome

Lynch syndrome (LS) is one of the most common hereditary cancer syndrome in human populations, associated with germline variants in MLH1, MSH2/EPCAM, MSH6 and PMS2 genes. The advent of next generation sequencing has proven a significant impact in germline variant detection in the causative genes; however, a large proportion of patients with clinical criteria still receive uncertain or negative results. PMS2 is the least frequent reported gene, associated with up to 15% of LS cases with late-onset disease and low penetrance phenotype; however, the proportion of PMS2-LS cases is considered to be highly underestimated. In this context, our analysis aimed to improve the current diagnostic yield by focusing on missense and intronic PMS2 variants available in public clinical databases (ClinVar, LOVD). We performed an in silico assessment of the wild-type DNA sequence and the reported genetic variants, employing splicing bioinformatics tools known for their effectiveness in other genes. Splicing variants were predicted in silico and using GTEx short-read RNA expression data. Out of the 2384 missense variants discovered, 90% were classified with uncertain significance (VUS). 4.9% of missense variants were shown to have a potential splicing consequence (DS > 0.2) using SpliceAI. As described in the original publication, SpliceAI-visual was proven effective in annotation of short intronic variants (< 50 bp). Four short intronic variants were identified using SpliceAI-visual as potentially splicing disturbing, in spite of using a lower threshold (DS > 0.1). Exons 2, 3, 4, 5, 6, 7, 8, 11, 12 and 14 were consistently predicted in at least three out of eight software with weak canonical splice sites. Additionally, we noted that both Exonic Splicing Enhancers (ESEs) and Exonic Splicing Silencers (ESSs) contribute significantly to alternative splicing and exonic selection in PMS2 gene. Specifically, ESE motifs were consistently more abundant in highly expressed exons 5, 11 and 14, while ESS motifs played a fundamental role in exons 6, 7 and 10. Computational analysis performed in our study serves as a valuable filtering step for guiding further RNA experiments. Additional functional data is necessary to validate our findings.

Association of a non-synonymous variant of MLH3 gene involved in meiotic recombination with conception rate of Japanese Black cattle

Context Conception rate, which is an important parameter to evaluate female fertility, has been gradually decreasing in Japanese Black cattle during the past decades. Meiosis is an essential biological process in gamete formation and meiotic failure could be a cause of infertility or reduced fertility in mammals. Of note, single nucleotide polymorphisms (SNPs) in the MLH3 gene involved in meiotic recombination were reported to affect the genome-wide recombination rate of meiosis in cattle. Aims The present study was conducted to investigate the association of SNPs in the MLH3 gene with conception rate in Japanese Black cattle. Methods On the basis of the reproductive data of 2045 Japanese Black cattle born from 1990 to 2009, we selected two groups of the reproductive females with high conception rate (n = 103) and low conception rate (n = 109). Then, we genotyped the SNPs in MLH3 gene in both reproductive groups by sequencing and polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP). The significant association of SNPs with conception rate in Japanese Black cattle was estimated by Fisher’s exact test, by using R commander. Key results We found the presence of five SNPs of MLH3 gene in Japanese Black cattle, including non-synonymous variants of MLH3 N408S that has been reported to be involved in meiotic recombination rate and MLH3 S591G newly identified in the present study. Comparison of genotype distributions and allele frequencies of the MLH3 N408S between high and low conception-rate groups indicated a significant difference between these groups, suggesting that this SNP is associated with conception rate. However, there is no significant difference between MLH3 S591G with conception rate in Japanese Black cattle. Conclusions We found a significant association between a non-synonymous variant of MLH3 N408S and conception rate, suggesting that this SNP can be a potential marker for selecting the Japanese Black cattle for improving fertility. We also identified a novel non-synonymous variant of MLH3 S591G in Japanese Black cattle. Implications These findings will be informative for future marker-assisted selection to improve the fertility of Japanese Black cattle. This is the first report of a genetic variant implicated in meiotic recombination being linked to female fertility in cattle.

CTIM-31. PRELIMINARY RESULTS OF A PHASE II STUDY OF STEREOTACTIC RADIOSURGERY IN CONJUNCTION WITH THE PD-1 INHIBITOR PEMBROLIZUMAB FOR THE TREATMENT OF RECURRENT HIGH-GRADE MENINGIOMA

Abstract Recurrence of higher-grade meningioma after initial resection and radiotherapy is frequent and associated with high rates of morbidity and mortality. Salvage therapies have limited efficacy and average survival after recurrence is approximately 5-10 years. We report here preliminary data from a phase 2 study combining immunotherapy with checkpoint inhibition with stereotactic radiosurgery for treatment of recurrent high-grade meningioma (NCT04659811). Adult patients with either grade 2 or 3 meningioma who have recurred despite treatment with surgery and radiation and who meet eligibility criteria received stereotactic radiosurgery, in 1 to 5 fractions, in conjunction with pembrolizumab 200mg on the first day of radiation and then every 3 weeks until progression, unacceptable toxicity or for 2 years. Primary objective is PFS12, and secondary objectives include safety of the combined treatment in recurrent meningioma, mOS, mPFS, and neurocognitive function and QOL metrics. To date we have enrolled 18 of planned 37 patients, 33% female, 39% grade 2 and 61% grade 3. Safety lead in was completed without any dose limiting toxicity. There have been 4 SAEs, only one of which was related to study treatment (cerebral edema). 29% of patients had at least one AE, the most common were GI disorders (23%), skin disorders (23%) and headache (17%). Preliminary data from 12 patients shows PFS12 to be 50%, which suggests that the combination of stereotactic radiosurgery may be more beneficial than treatment of Pembrolizumab alone (mPFS 7.6 months). One patient was found to have a homozygous focal deletion of the MLH1 gene and had a dramatic reduction in size of her meningioma with a durable response for over one year. These preliminary data suggest that the combination of stereotactic radiosurgery and pembrolizumab is safe, well tolerated and may be beneficial to patients with recurrent higher-grade meningioma.

IMMU-40. INVESTIGATING THE ROLE OF MUTATIONAL BURDEN IN TUMOR IMMUNOGENICITY USING A PRE-CLINICALMLH1-DEFICIENT GLIOBLASTOMA MODEL

Abstract BACKGROUND Although there is an established correlation between tumor mutational burden (TMB) and response to immune checkpoint inhibition (ICI) in many cancers, such an association has not been definitively shown in high-grade gliomas. Most studies of ICI therapy in gliomas, including glioblastoma (GBM), have failed to demonstrate efficacy, with the exception of hypermutated cases resulting from rare inherited defects in mismatch repair (MMR) genes. We sought to investigate the association of TMB to immune response using a syngeneic murine model with a spectrum of mutational burdens. METHODS We used CRISPR-Cas9 to knockout the MMR gene Mlh1 in the murine glioma model SB28, an ICI-resistant cell line with a very low mutational burden (108 non-synonymous mutations). RESULTS Single-cell sorted Mlh1 knockout SB28 clones revealed a two- to six-fold increase in TMB. Importantly, loss of Mlh1 also brought about global changes in immune- and inflammatory-related gene expression in vitro, without correlation to increasing TMB. While all clones had the same rate of in vitro proliferation, flank injection of a high TMB vs a low TMB SB28 Mlh1 knockout clone resulted in similar survival benefits compared to Mlh1 wildtype SB28. CONCLUSIONS These preliminary results suggest that, although disruption of the MMR system may result in heightened tumor immunogenicity, elevated TMB may not be the sole significant determinant. We are currently investigating tumor proliferation after flank injection in immunocompromised mice to confirm that slowed growth is immune-related, as well as clone-specific response to ICI treatment. We are also exploring the role of specific cytokines/chemokines in conferring this survival advantage and potential immune response. By generating a GBM model of varied mutational burdens and immune profiles and comparing to the baseline SB28 cell line, we can interrogate the relative significance of TMB in tumor immunogenicity and ICI response.

Lynch syndrome-associated and sporadic microsatellite unstable colorectal cancers: different patterns of clonal evolution yield highly similar tumours.

Microsatellite unstable colorectal cancer (MSI-CRC) can arise through germline mutations in mismatch repair (MMR) genes in individuals with Lynch syndrome (LS), or sporadically through promoter methylation of the MMR gene MLH1. Despite the different origins of hereditary and sporadic MSI tumours, their genomic features have not been extensively compared. A prominent feature of MMR-deficient genomes is the occurrence of many indels in short repeat sequences, an understudied mutation type due to the technical challenges of variant calling in these regions. In this study, we performed whole genome sequencing and RNA-sequencing on 29 sporadic and 14 hereditary MSI-CRCs. We compared the tumour groups by analysing genome-wide mutation densities, microsatellite repeat indels, recurrent protein-coding variants, signatures of single base, doublet base, and indel mutations, and changes in gene expression. We show that the mutational landscapes of hereditary and sporadic MSI-CRCs, including mutational signatures and mutation densities genome-wide and in microsatellites, are highly similar. Only a low number of differentially expressed genes were found, enriched to interferon-γ regulated immune response pathways. Analysis of the variance in allelic fractions of somatic variants in each tumour group revealed higher clonal heterogeneity in sporadic MSI-CRCs. Our results suggest that the differing molecular origins of MMR deficiency in hereditary and sporadic MSI-CRCs do not result in substantial differences in the mutational landscapes of these tumours. The divergent patterns of clonal evolution between the tumour groups may have clinical implications, as high clonal heterogeneity has been associated with decreased tumour immunosurveillance and reduced responsiveness to immunotherapy.

Association of glutaminase expression with immune-suppressive tumor microenvironment, clinicopathologic features, and clinical outcomes in endometrial cancer

ObjectiveIncreased glutamine metabolism by cancer cells via upregulation of the drug-targetable enzyme glutaminase may contribute to an immune-suppressive tumor microenvironment. Inhibiting glutamine metabolism can not only suppress tumor growth, but...

Reclassification of Two MLH1 Variants of Uncertain Significance Utilizing Clinical and Functional Data.

Pathogenic variants in the mismatch repair genes are associated with an elevated lifetime risk of colorectal cancer (CRC). We previously identified two variants of uncertain significance (VUS) in the MLH1 gene, c.696_698del, p.(Cys233del) and c.1919C > G, p.(Pro640Arg), in Danish families with numerous occurrences of CRC. To reclassify the variants we collected clinical data, initiated tumor and co-segregation analysis, and performed RNA splicing analysis, subcellular localization, and protein stability studies. The functional analysis revealed that the c.696_698del, p.(Cys233del) variant had an effect at the RNA level, on subcellular localization, and on protein stability, while the c.1919C > G, p.(Pro640Arg) variant showed decreased expression in localization studies and decreased protein stability. These results suggest both variants disrupt DNA mismatch repair. By applying all collected data and functional results we propose to reclassify the c.696_698del, p.(Cys233del) and the c.1919C > G, p.(Pro640Arg) variants as likely pathogenic (class 4) using MMR gene-specific ACMG/AMP guidelines. Consequently, the two MLH1 variants can now be used for risk assessment of variant carriers, while family members without the variants can be excluded from intensified cancer surveillance and follow population recommendations.

A collaborative review of the microsatellite instability/deficient mismatch repair phenotype in patients with upper tract urothelial carcinoma.

To perform a collaborative review of the literature exploring the microsatellite instability/deficient mismatch repair (MSI/dMMR) phenotype in patients with upper tract urothelial carcinoma (UTUC). A collaborative review of the literature available on Medline was conducted by the Cancer Committee of the French Association of Urology to report studies describing the genetic mechanisms, investigation, prevalence and impact of the MSI/dMMR phenotype in UTUC patients. The predominant genetic mechanism leading to the MSI/dMMR phenotype in UTUC patients is related to the constitutional mutation of one allele of the MMR genes MLH1, MSH2, MSH6 and PMS2 within Lynch syndrome. Indications for its investigation currently remain limited to patients with a clinical suspicion for sporadic UTUC to refer only those with a positive testing for germline DNA sequencing to screen for this syndrome. With regard to technical aspects, despite the interest of MSIsensor, only PCR and immunohistochemistry are routinely used to somatically investigate the MSI and dMMR phenotypes, respectively. The prevalence of the MSI/dMMR phenotype in UTUC patients ranges from 1.7% to 57%, depending on the study population, investigation method and definition of a positive test. Younger age and a more balanced male to female ratio at initial diagnosis are the main specific clinical characteristics of UTUC patients with an MSI/dMMR phenotype. Despite the conflicting results available in the literature, these patients may have a better prognosis, potentially related to more favourable pathological features. Finally, they may also have lower sensitivity to chemotherapy but greater sensitivity to immunotherapy. Our collaborative review summarises the available data from published studies exploring the MSI/dMMR phenotype in UTUC patients, the majority of which are limited by a low level of evidence.

Investigation of the Relationship Between DNA Mismatch Repair Genes and Microsatellite Instability in Solid Tumors

Aim: In this study, we aimed to detect the MSI status and somatic mutations in MMR genes (MSH2, MSH6, MLH1, PMS2) of a total of 55 solid tumors diagnosed with colorectal, endometrium and ovarian cancer by NGS method and to reveal the relationship between them. Material and Method: DNA isolation was performed by taking 10-micron sections from paraffin-embedded tissue samples of 55 patients diagnosed with kolorektal, endometrium ve ovarian solid tümörlerinin and Kapa NGS DNA extraction kit was used for sequence analysis. The purity and concentration of the DNA obtained was measured by Qubit fluoremeter, and NadPrep DNA Universal Library Preparation Kit was used for high quality library preparation. Bioinformatics analyses were performed on the Genomize Seq platform. The MSI value was analysed by Roche Navify Mutation Caller software and percentage MSI values were determined using the MSIsensor2 pipeline for secondary analysis of NGS. Results: All ovarian tumors were in the MSI-Stable category. The average MSI value was 2.01. One sample had an MSI of zero. In addition, no mutations in the MSH2 and MLH1 genes were detected in any of the ovarian tumors. 3 of 4 endometrial tumors were in the MSI-Stable category, and 1 tumor was in the MSI-low (MSI value: 13.2) category. No variants were detected in the MSH2 and PMS2 genes in endometrial tumors. 2 of the 41 colorectal tumors (Case4, Case16) were in the MSI-High category. No variants were detected in the MMR genes in 19 tumors. Conclusion: Although frame-shift and stop-gain mutations were detected in 23 tumors that would cause protein deficiency in MMR genes, MSI-H was not detected, as expected, except for two colorectal tumors. Therefore, the results of our study emphasise the need to define new predictive biomarkers clinically within the framework of algorithms to predict response to immunotherapy and determine prognosis.

The guidelines for clinical practice for carriers of germline mutations in the Lynch syndrome predisposition genes MLH1, MSH2, MSH6, PMS2 and large deletions of EPCAM (4.2024).

The guidelines for clinical practice for carriers of pathogenic variants in clinically relevant genes predisposing to Lynch syndrome and colorectal cancer define the steps of primary and secondary prevention that should be provided to the individuals at high risk of developing hereditary cancer in the Czech Republic. The drafting of the guidelines was organized by the Oncogenetics Working Group of the Society for Medical Genetics and Genomics of J. E. Purkyně Czech Medical Society, in cooperation with representatives of oncology, oncogynecology, and gastroenterology. The guidelines are based on the current recommendations of the National Comprehensive Cancer Network (NCCN), European Society of Medical Oncology (ESMO) and take into account the capacity of the Czech healthcare system.