Loss Of Mismatch Repair Proteins Research Articles

Mismatch repair protein deficiency and its implications on distant metastasis in colorectal cancer: A comprehensive analysis.

While previous studies have indicated variability in distant metastatic potential among different mismatch repair (MMR) states in colorectal cancer (CRC), their findings remain inconclusive, especially considering potential differences across various ethnic backgrounds. Furthermore, the gene regulatory networks and the underlying mechanisms responsible for these variances in metastatic potential across MMR states have yet to be elucidated. We collected 2058 consecutive primary CRC samples from the South West of China and assessed the expression of MMR proteins (MLH1, MSH2, MSH6, and PMS2) using immunohistochemistry. To explore the inconsistencies between different MMR statuses and recurrence, we performed a meta-analysis. To delve deeper, we employed Weighted Gene Co-expression Network Analysis (WGCNA), ClueGo, and iRegulon, pinpointing gene expression networks and key regulatory molecules linked to metastasis and recurrence in CRC. Lastly, both univariate and multivariate Cox regression analyses were applied to determine the impact of core regulatory molecules on metastasis. Of the samples, 8.2% displayed deficient MMR (dMMR), with losses of MLH1 and PSM2 observed in 40.8% and 63.9%, respectively. A unique 24.3% isolated loss of PMS2 without concurrent metastasis was identified, a result that diverges from established literature. Additionally, our meta-analysis further solidifies the reduced recurrence likelihood in dMMR CRC samples compared to proficient MMR (pMMR). Two gene expression networks tied to distant metastasis and recurrence were identified, with a majority of metastasis-related genes located on chromosomes 8 and 18. An IRF1 positive feedback loop was discerned in the metastasis-related network, and IRF1 was identified as a predictive marker for both recurrence-free and distant metastasis-free survival across multiple datasets. Geographical and ethnic factors might influence peculiarities in MMR protein loss. Our findings also highlight new gene expression networks and crucial regulatory molecules in CRC metastasis, enhancing our comprehension of the mechanisms driving distant metastasis.

Primary Papillary Colonic Adenocarcinoma With PDGFRA Mutation. A New Morphological Subtype? A Case Report and Review of Literature.

Classic colon carcinomas are defined as adenocarcinomas, characterized by groups of medium/large cells with basophilic and polymorphous nuclei and an eosinophilic elongated cytoplasm, that rearrange on glandular structures. Signs of poor prognosis include high tumor budding, lymphovascular and perineural invasion, poor differentiation, positive margins, and CDX2 loss. Less frequent colon carcinoma subtypes are: mucinous, medullary, signet-ring cell, squamous cell, small cell and undifferentiated carcinoma, among others. In the following case report, we present a 65-year-old woman with a T2N0Mx colon carcinoma with a remarkable papillary and follicular histological appearance. The immunohistochemical stains confirmed an intestinal origin (CDX2+) and excluded a thyroid, gynecological, and urological metastasis, with tumor cells negative for GATA3, PAX8, TTF-1, and thyroglobulin. There was no loss of mismatch repair proteins and p53 showed a wild-type staining. next generation sequencing showed a platelet-derivated growth factor receptor alpha (PDGFRA) mutation. To the best of our knowledge, there have been only two examples of primary papillary colon carcinoma reported in the literature, and neither of them with a PDGFRA mutation. We describe one tumor and discuss its pathological features.

Clinical Significance of Tumor Immune Microenvironment in Endometrial Endometrioid Carcinoma, Grade 1 With DNA Mismatch Repair Protein Loss.

The administration of immune checkpoint inhibitors (ICIs) is increasing in endometrial cancer, especially in the mismatch repair (MMR)-deficient group. To prevent unnecessary immune-related adverse events, ICIs need to be administered to more appropriate patients. The tumor immune microenvironment has been reported to be a predictive marker of the efficacy of ICI therapies. This study evaluated CD8, FoxP3, CD68, PD-L1, and β-catenin expression in endometrial endometrioid carcinoma, grade 1 (G1) with DNA mismatch repair protein loss (MMR loss), and their association with clinicopathological features. We retrospectively analyzed tumor samples from 107 patients with endometrial endometrioid carcinoma, G1 (MMR-deficient group: n=67; MMR-proficient group: n=40). Overall, 47 cases of MLH1/PMS2 loss and 20 cases of MSH2/MSH6 loss were observed. The patients with low intraepithelial CD8 expression significantly more frequently exhibited deep myometrial invasion, and the elderly group (≥60 y) significantly more frequently showed low stromal CD8 expression. In addition, FoxP3-positive cell count and FoxP3/CD8+ ratio were significantly correlated with the International Federation of Obstetrics and Gynecology 2023 stage and lymph node metastasis. In the Kaplan-Meier analysis, the patients with low intraepithelial or stromal CD8 expression had shorter progression-free survival (PFS) than those with high intraepithelial or stromal CD8 expression, albeit not significantly. We clarified that the tumor immune microenvironment had an impact on clinicopathological features within the group with MMR loss, which is the main target for ICIs, limited to endometrioid carcinoma, G1. Further studies are needed, including on patients administered ICIs.

Characterization of sessile serrated adenomas with dysplasia including intramucosal adenocarcinoma and colorectal carcinoma with a microsatellite instability phenotype

Recent studies have shown that sessile serrated lesions (SSLs) lead to the development of colorectal cancer (CRC) with a microsatellite instability (MSI) phenotype via a dysplasia-carcinoma sequence. However, the pathological and molecular mechanisms of SSL with dysplasia (SSLD) are unclear. Here, we aimed to examine the clinicopathological and molecular alterations in SSLD and to evaluate the significance of such alterations with regard to lesion progression. Fifty-four SSLDs (20 serrated dysplasia cases and 17 intestinal dysplasia cases, including 30 low-grade dysplasia [LGD] cases, 7 high-grade dysplasia [HGD] cases, and 17 intramucosal adenocarcinomas [IMAs]) were evaluated. Molecular alterations, including immunohistochemical expression of various markers, DNA methylation status, and multiple genetic mutations (using next-generation sequencing), were assessed. Additionally, such alterations were also investigated in 41 CRCs with an MSI phenotype (invasion beyond submucosa). The frequency of mismatch repair (MMR) deficiency in SSLD was 12 of 39 cases (32.4 %), whereas the MMR proficient type was observed in 17 of 39 SSLD cases. SSLD with serrated dysplasia showed a significantly higher frequency of loss of MMR protein expression and methylation status. Moreover, loss of MMR protein expression differed significantly between LGD and IMA. Furthermore, the frequency of TP53 mutation was significantly higher in IMA than in LGD. The current findings demonstrated that SSL with serrated dysplasia may be associated with an increased risk of malignant transformation compared with intestinal dysplasia. Loss of MMR proteins and mutation of TP53 may play important roles in tumor progression from dysplasia to carcinomatous lesions.

Analysis of clinicopathological features and prognosis of sporadic synchronous multiple primary colorectal cancers

Analysis of clinicopathological features and prognosis of sporadic synchronous multiple primary colorectal cancers

Diffuse Large B-Cell Lymphoma Has a Low Frequency of dMMR and High Frequencies of DNA Mismatch Repair Protein High Expression Associated with Lower T-Cell Infiltration

Background: DNA mismatch repair (MMR) deficiency (dMMR), which leads to genomic and microsatellite instability, is a biomarker that predicts response to immunotherapies and has variable prognostic effects for chemotherapies in solid tumors. The dMMR can be detected using gene sequencing or immunohistochemistry for four essential MMR proteins: MSH6, MSH2, MLH1, and PMS2. Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive lymphoma. Previous studies have suggested the role of MMR gene variants in DLBCL lymphomagenesis, yet the prognostic role of dMMR in DLBCL has not been well studied. Methods: We performed targeted next-generation sequencing and immunohistochemistry for MSH6, MSH2, MLH1, and PMS2 in a large cohort of DLBCL patients treated with standard chemoimmunotherapy. Gene expression profiling (GEP) was performed using the Affymetrix GeneChip Human Genome HG-U133 Plus 2.0 microarray (data in GSE31312). Fluorescent multiplex immunohistochemistry (mIHC) was performed using MultiOmyx multiplexing immunofluorescence staining protocols and antibodies against 13 immune markers. We investigated the frequencies of dMRR and MMR protein expression and correlated the mutation status and expression levels with patient survival and DLBCL biology, including the number of mutated genes, GEP data, previously analyzed DLBCL biomarkers, and immune cell immunophenotypes. Results: MMR gene mutations and loss of MMR protein expression were infrequent in DLBCL (Figure A) and did not show a significant prognostic impact. MMR proteins were commonly expressed in DLBCL samples and the germinal centers of reactive tonsil controls (Figure B), with higher mean and median percentages of tumor cells expressing MSH6 and MLH1 proteins than in the solid tumor samples used for comparison. High expression of MMR proteins was associated with Ki-67, MYC, and p53 overexpression as determined by immunohistochemistry. GEP analysis identified significantly upregulated genes involved in the mitotic cell cycle and DNA metabolism and prominent downregulated immune gene signatures in DLBCL with high MMR protein expression. Fluorescent mIHC confirmed the associations with decreased T cell abundance in MSH6/MSH2/MLH1/PMS2 highly expressing DLBCL (Figure C) independent of p53 and MYC expression status, whereas MSH6/ MLH1 mutations were associated with increased T cell frequencies. High versus low expression of MSH6, MLH1, and PMS2 showed significant unfavorable prognostic effects in DLBCL when the optimal cutoffs were used for high expression. However, when the median percentages were used as cutoffs, the prognostic effects were not significant; nonetheless, MSH6 and PMS2 high expression showed significant adverse prognostic effects in the MYC¯ DLBCL subset. Interestingly, when we used Ki-67, MYC + or BCL2 + percentages in DLBCL assessed by immunohistochemistry to subtract MMR protein percentages and then correlated the differences to survival, we found significant favorable prognostic impact by higher percentage expression differences between MMR proteins and BCL2, or by intermediately higher differences between MMR proteins and MYC. For MSH2/MLH1/PMS2, the higher percentages compared with MYC/BCL2 showed no significant correlations with T cell infiltration levels, whereas the higher differences between MSH6 and MYC/BCL2 were associated with significantly lower T cell frequencies (Figure D). Conclusions: This study revealed that high expression of MMR proteins is a common feature of DLBCL associated with lower tumor-infiltrating T cells, MYC and p53 overexpression, and context-dependent prognostic effects. In contrast, dMMR and loss of MMR proteins are infrequent and have no significant prognostic effects in DLBCL treated with standard chemoimmunotherapy. These results may have implications for understanding DLBCL biology and the low efficacy of PD-1 blockade immunotherapy in DLBCL.

Immunohistochemical characteristics and potential therapeutic regimens of hepatoid adenocarcinoma of the stomach: a study of 139 cases.

Hepatoid adenocarcinoma of stomach (HAS) is a special subtype of gastric cancer with poor prognosis. Immunohistochemical analysis could provide important clues for the treatment of HAS. A total of 159 patients were diagnosed as HAS and 139 were enrolled in this study. Statistical differences were determined using relative test methods and survival analyses were performed by the Kaplan-Meier method to find survival differences. All tumors in this study were negative for Epstein-Barr virus-encoded small RNAs (EBERs) and almost all showed no loss of mismatch repair (MMR) proteins and were positive for alpha fetoprotein (AFP or spalt like transcription factor 4 (SALL4). About half of the tumors had a positive programmed death-ligand 1 combined positive score (CPS) and 17.3% were positive for human epidermal growth factor receptor 2 (HER2). In addition, there was a relatively high proportion of cmet expression. We also found that HAS patients with recurrent disease treated by emerging therapy had a better survival than those treated with traditional chemotherapy (p = 0.002, median recurrence-to-death survival: 23 months versus 6 months); HAS patients who received anti-HER2 therapy or harbored MMR deficiency had favorable prognosis. Overall, high proportions of MMR protein proficiency, positivity for AFP or SALL4, overexpression of HER2, CPS and cmet, as well as negative EBER findings, are distinctive characteristics of HAS patients. While negative EBER and MMR proficiency indicate molecular features of HAS, positivity for AFP or SALL4 could aid in the diagnosis of HAS. In addition, HAS patients could benefit from anti-HER2 therapy, immunotherapy, and anti-angiogenesis therapy.

Clinicopathological and molecular pathological characteristics in tamoxifen‑related endometrial cancer.

Tamoxifen (TAM), a selective estrogen receptor modulator, is often used for long-term adjuvant endocrine therapy in patients with hormone receptor-positive breast cancer. TAM is known to increase the risk of endometrial cancer (EC); however, the mechanism has not yet been fully elucidated. Therefore, molecular genetic analysis of EC following TAM administration (TAM-related EC) was conducted. A total of 10 samples of TAM-related EC and 20 sporadic EC samples (as controls) were analyzed. Copy number variation analysis was conducted, microsatellite instability (MSI) status was assessed, and mismatch repair (MMR) protein expression was examined immunohistochemically. Copy number variation analysis revealed that KDR, NOTCH1, NTRK1, NTRK3 and PDGFRB were more frequently amplified in TAM-related EC (P=0.039, P<0.001, P=0.011, P=0.006 and P=0.035, respectively). In MSI analysis, 4 cases were classified as MSI-high (40%), which is a higher frequency compared with that among patients with sporadic EC (~10% in Japanese women). Loss of MMR proteins was confirmed in all MSI-high cases. In 1 MSI-high case, a benign lesion of hyperplasia prior to EC development was also MSI-high with loss of some MMR protein expression. Several genes were specifically amplified in TAM-related ECs. Furthermore, TAM-related ECs were frequently MSI-high. Further studies are required to be conclusive; however, the present findings may lead to a reduction of unnecessary gynaecological testing in clinical practice and also encourage the testing for MSI status for optimal individualized treatment.

Clinicopathological characteristics, molecular landscape, and biomarker landscape for predicting the efficacy of PD-1/PD-L1 inhibitors in Chinese population with mismatch repair deficient urothelial carcinoma: a real-world study.

Urothelial carcinoma (UC) with deficient mismatch repair (dMMR) is a specific subtype of UC characterized by the loss of mismatch repair (MMR) proteins and its association with Lynch syndrome (LS). However, comprehensive real-world data on the incidence, clinicopathological characteristics, molecular landscape, and biomarker landscape for predicting the efficacy of PD-1/PD-L1 inhibitors in the Chinese patients with dMMR UC remains unknown. We analyzed 374 patients with bladder urothelial carcinoma (BUC) and 232 patients with upper tract urothelial carcinoma (UTUC) using tissue microarrays, immunohistochemistry, and targeted next-generation sequencing. Results showed the incidence of dMMR UC was higher in the upper urinary tract than in the bladder. Genomic analysis identified frequent mutations in KMT2D and KMT2C genes and LS was confirmed in 53.8% of dMMR UC cases. dMMR UC cases displayed microsatellite instability-high (MSI-H) (PCR method) in 91.7% and tumor mutational burden-high (TMB-H) in 40% of cases. The density of intratumoral CD8+ T cells correlated with better overall survival in dMMR UC patients. Positive PD-L1 expression was found in 20% cases, but some patients positively responded to immunotherapy despite negative PD-L1 expression. Our findings provide valuable insights into the characteristics of dMMR UC in the Chinese population and highlights the relevance of genetic testing and immunotherapy biomarkers for treatment decisions.

Comprehensive assessment of mismatch repair and microsatellite instability status in molecular classification of endometrial carcinoma

Objective: To explore the concordance and causes of different mismatch repair (MMR) and microsatellite instability (MSI) detection results in endometrial carcinoma (EC) molecular typing. Methods: A total of 214 EC patients diagnosed from January 2021 to April 2023 were selected at the Department of Pathology, Peking University Third Hospital. The immunohistochemistry (IHC) results of MMR protein were reviewed. Tumor specific somatic mutations, MMR germline mutations, microsatellite scores and tumor mutation burden (TMB) were detected by next-generation sequencing (NGS) with multi-gene panel. Methylation-specific PCR was used to detect the methylation status of MLH1 gene promoter in cases with deficient MLH1 protein expression. In cases with discrepant results between MMR-IHC and MSI-NGS, the MSI status was detected again by PCR (MSI-PCR), and the molecular typing was determined by combining the results of TMB and MLH1 gene promoter methylation. Results: (1) In this study, there were 22 cases of POLE gene mutation subtype, 55 cases of mismatch repair deficient (MMR-d) subtype, 29 cases of p53 abnormal subtype, and 108 cases of no specific molecular profile (NSMP). The median age at diagnosis of MMR-d subtype (54 years old) and the proportion of aggressive histological types (40.0%, 22/55) were higher than those of NSMP subtype [50 years old and 12.0% (13/108) respectively; all P<0.05]. (2) Among 214 patients, MMR-IHC test showed that 153 patients were mismatch repair proficient (MMR-p), 49 patients were MMR-d, and 12 patients were difficult to evaluate directly. MSI-NGS showed that 164 patients were microsatellite stable (MSS; equal to MMR-p), 48 patients were high microsatellite instability (MSI-H; equal to MMR-d), and 2 patients had no MSI-NGS results because the effective sequencing depth did not meet the quality control. The overall concordance between MMR-IHC and MSI-NGS was 94.3% (200/212). All the 12 discrepant cases were MMR-d or subclonal loss of MMR protein by IHC, but MSS by NGS. Among them, 10 cases were loss or subclonal loss of MLH1 and (or) PMS2 protein. Three discrepant cases were classified as POLE gene mutation subtype. In the remaining 9 cases, 5 cases and 3 cases were confirmed as MSI-H and low microsatellite instability (MSI-L) respectively by MSI-PCR, 6 cases were detected as MLH1 gene promoter methylation and 7 cases demonstrated high TMB (>10 mutations/Mb). These 9 cases were classified as MMR-d EC. (3) Lynch syndrome was diagnosed in 27.3% (15/55) of all 55 MMR-d EC cases, and the TMB of EC with MSH2 and (or) MSH6 protein loss or associated with Lynch syndrome [(71.0±26.2) and (71.5±20.1) mutations/Mb respectively] were significantly higher than those of EC with MLH1 and (or) PMS2 loss or sporadic MMR-d EC [(38.2±19.1) and (41.9±24.3) mutations/Mb respectively, all P<0.01]. The top 10 most frequently mutated genes in MMR-d EC were PTEN (85.5%, 47/55), ARID1A (80.0%, 44/55), PIK3CA (69.1%, 38/55), KMT2B (60.0%, 33/55), CTCF (45.5%, 25/55), RNF43 (40.0%, 22/55), KRAS (36.4%, 20/55), CREBBP (34.5%, 19/55), LRP1B (32.7%, 18/55) and BRCA2 (32.7%, 18/55). Concurrent PTEN, ARID1A and PIK3CA gene mutations were found in 50.9% (28/55) of MMR-d EC patients. Conclusions: The concordance of MMR-IHC and MSI-NGS in EC is relatively high.The discordance in a few MMR-d EC are mostly found in cases with MLH1 and (or) PMS2 protein loss or MMR protein subclonal staining caused by MLH1 gene promoter hypermethylation. In order to provide accurate molecular typing for EC patients, MLH1 gene methylation, MSI-PCR, MMR gene germline mutation and TMB should be combined to comprehensively evaluate MMR and MSI status.

The prevalence of lynch syndrome (DNA mismatch repair protein deficiency) in patients with primary localized prostate cancer using immunohistochemistry screening

BackgroundProstate cancer is one of the most heritable human cancers. Lynch syndrome is an autosomal dominant inheritance caused by germline mutations in DNA mismatch repair (MMR) genes, which are also associated with an increased incidence of prostate cancer. However, prostate cancer has not been defined as a Lynch syndrome-associated cancer. The proportion of Lynch syndrome patients in primary prostate cancers is unclear. In this study, we investigated MMR protein loss using universal immunohistochemical screening to determine the prevalence of Lynch syndrome in patients with localized prostate cancer who underwent radical prostatectomy.MethodsOne hundred twenty-nine surgical specimens from radical prostatectomy performed at Toranomon Hospital between 2012 and 2015 were retrospectively tested using universal screening with immunohistochemistry staining for expression of the MMR proteins MLH1, PMS2, MSH2, and MSH6. For all suspected MMR-deficient patients, germline genetic tests focusing on MMR genes were performed.ResultsMMR protein loss was found in only one patient (0.8%) who showed dual MSH2/MSH6 loss. This patient showed a single nucleotide pathogenic germline mutation from c.1129 C to T (p.Gln377*) at exon 7 in the MSH2 gene. He was diagnosed with a primary prostate cancer at 66 years of age. He had a documented history of Lynch syndrome (Muir–Torre syndrome) with previous colon cancer, sebaceous tumor, and keratoacanthoma as well as subsequent bladder cancer, all of which also showed dual MSH2/MSH6 loss. He also had a strong family history of colorectal and other Lynch syndrome-associated cancers. The pathological stage was pT3aN0M0, and the pathological grade was Gleason 7(4 + 3) with tertiary pattern 5.ConclusionsIn this study, immunohistochemical screening of MMR proteins for Lynch syndrome was performed in a series of prostate cancer cases. The prevalence of Lynch syndrome in localized prostate cancer was 0.8%, which is low compared with other Lynch syndrome-associated cancers.

Molecular classification of endometrial carcinoma-ashort summary for clinical use

Histopathological examination is still the backbone for the diagnosis and treatment decision making in endometrial carcinoma (EC). The binary classification of EC into type1 (mostly endometrioid) and type2 (mostly serous), although still helpful, showed overlapping clinical, morphological and molecular features and was not very prognostic discriminatory for all subtypes of EC. Analysing the most recent studies dealing with the molecular classification of EC and the recommendations of the German S3-guidelines for EC. Based on the comprehensive molecular study of The Cancer Genome Atlas Project (TCGA) four distinct molecular subtypes have been identified: EC with POLE mutation (POLEmut), with loss of mismatch repair proteins (MMR deficiency; dMMR), or with TP53 mutation (p53mut) and without any of these alterations, termed NSMP (no specific molecular profile). The molecular classification of EC presents amorphomolecular approach, based on histopathological evaluation (tumor diagnosis, subtyping, grading), immunohistochemistry (MMR, p53) and molecular analyses for POLE. The incorporation of this molecular classification is recommended for clinical use by the World Health Organisation (WHO) as well as many national guidelines and international societies. Due to the heterogeneity of NSMP-EC, which is the largest molecular group, additional research is indicated to further characterise these tumors.

Concordance between microsatellite instability testing and immunohistochemistry for mismatch repair proteins and efficient screening of mismatch repair deficient gastric cancer.

Microsatellite instability (MSI) testing, an established technique that has gained prominence in recent years for its predictive potential regarding the efficacy of immune checkpoint inhibitors, is used to evaluate DNA mismatch repair (MMR) deficiency (dMMR). As with other methods, the immunohistochemistry (IHC) of MMR proteins is also widely adopted. Although both techniques have been validated, their concordance rate remains unknown, particularly regarding non-colorectal cancer. Therefore, the aim of the present study was to explore and elucidate their concordance in the context of gastric cancer (GC). A total of 489 surgically resected primary GC tissues were analyzed to compare the results yielded by the MSI test and those from IHC. Of 488 GC cases, 56 (11.5%) exhibited a loss of MMR proteins, whereas 52 (10.7%) were classified as high-frequency MSI (MSI-H). The concordance rate between these two categories was 99.2%. The microsatellite markers BAT26 and MONO27 demonstrated 100% sensitivity and 99.5% specificity in detecting dMMR GC. In addition, histopathological analysis revealed that MSI-H was more prevalent in GCs exhibiting coexisting Tub2 and Por1 subtypes. However, four discordant cases were observed. All four cases were microsatellite-stable cases but exhibited loss of MLH1 protein expression with hypermethylation of the MLH1 promoter. The results of the present study highlight that while there is a strong concordance between MSI and IHC testing results for determining dMMR status, IHC testing may offer superior efficacy in detecting dMMR.

Mismatch Repair Deficiency in Biliary Tract Cancer: Prognostic Implications and Correlation with Histology

Introduction: Mismatch repair (MMR) deficiency represents a biomarker and therapeutic target in various neoplasms, but its role in biliary tract cancers (BTCs) remains misunderstood. Methods: MMR status was retrospectively assessed using immunohistochemistry in 163-BTCs patients. We identified MMR proficiency (pMMR)/deficiency (dMMR) according to the loss of MMR proteins (MLH1, PMS2, MSH2, MSH6). The primary objective of the study was to assess the incidence of dMMR in BTCs; the secondary purpose was to explore its association with prognosis and clinical features. Results: dMMR was recorded in 9 patients, and it was strongly associated with mucinous histology (p < 0.01). Regarding the prognostic effect, in 122-radically resected patients, disease-free survival (DFS) resulted significantly shorter in dMMR patients compared to pMMR patients (10.7 vs. 31.3 months, p = 0.025) and so did nodal status (48.2 vs. 15.3 months in N0 vs. N+) (p < 0.01). Moreover, dMMR confirmed its prognostic role in terms of DFS at multivariate analysis (p = 0.03), together with nodal status (p = 0.01), and resection margin (p = 0.03). In 103 M+ patients (encompassing 41 metastatic de novo and 62 recurred after surgery patients) there were not differences between dMMR and pMMR regarding survival analyses. Conclusions: dMMR status is strongly correlated with mucinous histology and represents an independent prognostic factor in terms of disease relapse in patients with resected BTC. Implications for Practice: MMR may play an independent role in promoting an aggressive behaviour in patients with radically resected BTC. These results could be useful in improving the selection of patients after resection and, above all, should justify the evaluation of MMR status as a therapeutic target in BTC, especially in patients with atypical histology.

Mismatch Repair Protein Expression in Endometrial Cancer: Assessing Concordance and Unveiling Pitfalls in Two Different Immunohistochemistry Assays.

This study aimed to compare the concordance and interchangeability of the Dako/Agilent and Ventana/Roche mismatch repair (MMR) immunohistochemistry (IHC) assays commonly used in pathology. It also aimed to provide diagnostic insights by examining the frequency and characteristics of the dot-like artifact observed in MLH1 M1 clone staining in endometrial cancer. Fifty endometrial cancer cases with MMR deficiency, excised between 2011 and 2018, were included in the study. IHC was performed using primary antibody clones from Ventana/Roche (MLH1, clone M1; MSH2, G219-1129; MSH6, SP93; PMS2, A16-4) and Dako/Agilent (MLH1, ES05; MSH2, FE11; MSH6, EP49; PMS2, EP51). Both assays were conducted using respective autostainers. The Dako/Agilent assay showed a loss of MLH1 in 26 cases, MSH2 in 12 cases, MSH6 in 23 cases, and PMS2 in 28 cases. The two assays had a complete agreement in MMR protein expression or loss. The dot-like artifact in MLH1 M1 clone staining was observed in 77% (20/26) of cases, predominantly in the surface area of the tumor, ranging from 5% to 40% (median: 10%). These findings highlight the high concordance between the MMR-IHC assays and emphasize the importance of considering the dot-like artifact in MLH1 M1 clone staining when diagnosing endometrial cancer with MMR deficiency.

BI09 Microsatellite instability and loss of mismatch repair proteins in nonmelanoma skin cancer and treatment-resistant phenotypically distinct precancerous lesions in Muir–Torre/Lynch syndrome: a multicentre retrospective study

Abstract DNA mismatch repair (MMR) gene mutations resulting in microsatellite instability (MSI) are associated in the pathogenesis of Muir–Torre syndrome (MTS), a variant of Lynch syndrome (LS). It is characteristically defined by the association of at least one sebaceous skin neoplasm and/or keratoacanthoma and a visceral malignancy. The presence of cutaneous lesions plays a vital role in the early detection and preventive cancer screening of the disease; however, nonmelanoma skin cancers (NMSCs) and their precursors are seldom reported. We conducted a retrospective multicentre study between 2011 and 2022 of adults with a confirmed genetic diagnosis of MTS/LS across two specialist institutions presenting with phenotypically distinct treatment-resistant precancerous skin lesions and/or NMSC with the associated loss of MMR expressions consistent with their germline mutations which are currently not recognized diagnostic features. Median age at the onset of precancerous/NMSC in eight individuals was 57.5 years, with an equal sex distribution. Lesions occurred mostly on the face (n = 14), followed by the forearms (n = 8), dorsum of the hands (n = 9), the legs (n = 4) and the chest (n = 1). Our study histologically and immunohistochemically examined MMR expressions and MSI in 20 precancerous and/or NMSCs. Loss of expression and MSI were found in actinic keratoses (AK) (n = 6/7), disseminated superficial actinic porokeratosis (DSAP; n = 1/2), squamous cell carcinoma (n = 4/5) and basal cell carcinoma (n = 4/4). Additionally, we found sebaceomas with atypia (n = 2/2). In 17 lesions, the loss of MMR expression and MSI were consistent with their germline mutations. We also discovered that all lesions identified with MSI had normal adjacent skin with no loss of MMR expression. Our observations suggest the detection of MSI, and MMR gene abnormality, play a critical role in the development of precancerous and NMSC other than sebaceous neoplasms in this disease. To date, the diagnostic criteria for MTS/LS do not include NMSC and their precursors, and these have rarely been reported. We note a clinically distinct presentation of widespread erythematous scaly lesions resembling AK/DSAP, resistant to multiple treatments, which is an additional recognizable clinical feature in this patient subgroup. This is an important association in cancer-prone individuals and immunohistochemistry testing for MMR genes should be encouraged. This can be a powerful investigative tool as AK/DSAP are easily identifiable, numerous and readily accessible for DNA analysis; therefore, detecting the presence of MSI in the skin may aid in screening individuals promptly. MTS/LS is best managed by a multidisciplinary team with close surveillance for visceral malignancies, highlighting the importance of routine monitoring for precancerous and nonsebaceous skin cancers.

Somatic Sequencing and Microsatellite Instability Results From Mismatch Repair-deficient Endometrial Carcinoma Patients Without Lynch Syndrome ("Lynch-like" tumors): Implications for Heritable Cancer Screening, Molecular Prognostication, and Immunotherapeutic Vulnerability.

Immunostaining of endometrial carcinomas for mismatch repair (MMR) protein loss is standard-of-care for Lynch syndrome screening, but also identifies MMR-deficient tumors without germline pathogenic variants. While the majority show MLH1 hypermethylation (MLH1hm), somatic MMR pathogenic variants are increasingly recognized drivers of immunohistochemistry-germline discordance. Because MMR abnormalities with both germline and somatic origins have prognostic significance and impart susceptibility to immune checkpoint inhibitors, it is important to understand how frequently tumors with MMR immunohistochemical loss and normal germline testing ("Lynch-like" tumors) have underlying somatic MMR pathogenic variants. Somatic tumor sequencing±microsatellite instability (MSI) testing was performed on 18 endometrial cancers with MMR immunohistochemical loss but negative MMR germline results and negative MLH1hm where relevant. Tumor sequencing and MSI testing were successful in 94%. Where successful, 80% were MSI-high and 94% had a molecular correlate for the initial immunohistochemical interpretation. The single case without an identified somatic pathogenic variant was MSI-low and initially showed loss of MSH6 by immunohistochemistry but with extremely limited internal control staining. On review, MSH6 immunohistochemistry was reclassified as equivocal, and repeat staining revealed improved control expression with intact MSH6. Following reclassification of this case, 100% tumors with MMR deficiency by immunohistochemistry had at least 1 confirmed somatic MMR pathogenic variant, and 86% were MSI-high. These results demonstrate that when correctly interpreted immunohistochemistry is a strong surrogate for somatic MMR pathogenic variants and support its use as the frontline MMR biomarker in endometrial cancer for heritable screening, molecular prognostic classification, and immunotherapeutic biomarker testing purposes.

Locally advanced rectal cancer patients with mismatch repair protein deficiency can obtain better pathological response after regional chemoembolization.

Preoperative transcatheter rectal arterial chemoembolization (TRACE) can enhance the pathological response rate in some patients with locally advanced rectal cancer (LARC). However, how to accurately identify patients who can benefit from this neoadjuvant modality therapy remains to be further studied. Deficient mismatch repair (dMMR) protein plays a crucial role in maintaining genome stability. A proportion of patients with rectal cancer are caused by the loss of mismatch repair (MMR) protein. Given the role of MMR in guiding the efficacy in patients with colorectal carcinoma (CRC), this study is designed to evaluate the effect of dMMR status on the response to neoadjuvant therapy through a retrospective analysis. We launched a retrospective study. First, we selected patients with LARC from the database, and these patients had received preoperative TRACE combined with concurrent chemoradiotherapy. Then, the tumor tissue biopsied by colonoscopy before intervention was taken for immunohistochemistry. According to the expression of MLH-1, MSH-2, MSH-6 and PMS-2, these patients were divided into dMMR protein group and proficient MMR (pMMR) protein group. All patients underwent pathological examination at the end of neoadjuvant therapy, either surgically excised tissue or colonoscopically biopsied tissue. The end point was the pathologic complete response (pCR) after TRACE combined with concurrent chemoradiotherapy. From January 2013 to January 2021, a total of 82 patients with LARC received preoperative TRACE combined with concurrent chemoradiotherapy, and the treatment was well tolerated. Among 82 patients, there were 42 patients in the pMMR group and 40 patients in the dMMR group. 69 patients returned to the hospital for radical resection. In 8 patients, the colonoscopy showed good tumor regression grade after 4 weeks of interventional therapy and refused surgery. The remaining five patients were neither surgically treated nor reexamined by colonoscopy. 77 patients were eventually enrolled in the study. Individually, the pCR rates of these two groups (10%, 4/40 vs. 43%, 16/37) showed significant difference (P < 0.05). Biomarker analysis indicated that patients with dMMR protein had a better propensity for pCR. In patients with LARC, preoperative TRACE combined with concurrent chemoradiotherapy showed good pCR rates, especially in patients with dMMR. Patients with MMR protein defects have a better propensity for pCR.

Abstract 5285: Identification of therapeutic targets in poorly differentiated carcinoma through a multimodal molecular analysis

Abstract Poorly differentiated thyroid carcinoma (PDTC) represents a rare subtype of thyroid cancer with aggressive clinical course and peculiar clinical and pathological characteristics. Recent genetic studies highlighted the main molecular pathways involved in its pathogenesis but data are affected by heterogeneity of case selection and relatively limited sample size. Using a multimodal molecular approach, aim of this project was to implement the PDTC molecular characterization and to identify novel prognostic biomarkers and potential therapeutic targets. A total of 84 cases of PDTC classified according to the Turin proposal were selected from a multi-Institutional series. Fifty-nine samples underwent DNA, RNA and protein analyses. Mismatch repair (MMR) defects were tested using immunohistochemistry for MLH1, MSH2, MSH6 and PMS2. DNA and RNA analyses were performed by means of next generation sequencing (NGS) using Oncomine Comprehensive assay V3. Due to the high failure rate in RNA analysis, gene fusion analysis was enriched by 25 additional samples. MMR protein loss was observed in 7/59 samples (11.9%). In NGS DNA analyses, 51/59 cases were adequate. The most prevalent mutations were in NRAS (13/51, 25%) and TP53 (13/51, 25%), all mutually exclusive each other. TERT promoter (TERTp) mutations were detected in 11/51 of cases (21.6%). Other genes with a relevant prevalence were PTEN (15.7%), NF1 (13.7%), ATM (13.7%), NOTCH3 (11.8%) and BAP1 (11.8%). Mean number of alterations was higher in TP53-mutated cases (5.8 mutations/case) than in RAS-mutated cases (2.8 mutations/case). TP53-mutated samples lacked TERTp co-mutations but were associated with mutations in PTEN and in genes related to MMR system and/or loss of MMR proteins. PIK3CA was the most prevalent co-mutated gene (three samples) in RAS-mutated cases. A third group (25 cases) lacked RAS or TP53 mutations, had a low mean number of alterations (2.7 mutations/case) and was enriched for TERTp mutations (up to 32%). Copy number variations were not detected. Among the 43 cases adequate for NGS RNA analysis, gene fusions in PAX8-PPARG (one case) and TBL1XR1-PIK3CA (two cases) were detected. This latter fusion has never been reported in thyroid cancer, and was validated by fluorescence in situ hybridization (FISH). In conclusion, PDTC are genomically clustered into RAS-mutated tumors (with low mutational burden and co-mutations affecting genes involved in the same pathway), TP53-mutated cancers (with high mutational burden, absence of TERTp mutations and strong association with MMR defects) and a third “double negative” group enriched for TERTp mutations. Overall, targetable gene fusions have a prevalence of 7%. Moreover, 38% of overall cases harbor mutations in genes coding for tyrosine kinases potentially targetable and/or have defects in the MMR that claim a potential role for immunotherapy. Citation Format: Vanessa Zambelli, Marta Fornaro, Giulia Orlando, Ida Rapa, Francesca Napoli, Susanna Cappia, Lorenzo Daniele, Simonetta Piana, Mauro Papotti, Marco Volante. Identification of therapeutic targets in poorly differentiated carcinoma through a multimodal molecular analysis. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5285.

Highly Sensitive Microsatellite Instability and Immunohistochemistry Assessment in Endometrial Aspirates as a Tool for Cancer Risk Individualization in Lynch Syndrome

Women with Lynch syndrome (LS) are at increased risk of endometrial cancer (EC), among other tumors, and are characterized by mismatch repair (MMR) deficiency and microsatellite instability (MSI). While risk-reducing gynecologic surgeries effectively decrease EC incidence, doubts arise regarding the appropriate timing of the surgery. We explored the usefulness of highly sensitive MSI (hs-MSI) assessment in endometrial aspirates for individualizing gynecologic surveillance in LS carriers. Ninety-three women with LS, 25 sporadic EC patients (9 MMR-proficient and 16 MMR-deficient), and 30 women with benign gynecologic disease were included in this study. hs-MSI was assessed in prospectively collected endometrial aspirates in 67 LS carriers, EC cases, and controls. MMR, PTEN, ARID1A, and PAX2 protein expression patterns were evaluated in the LS samples. Follow-up aspirates from 8 LS carriers were also analyzed. Elevated hs-MSI scores were detected in all aspirates from MMR-deficient EC cases (3 LS and 16 sporadic) and negative in aspirates from controls and MMR-proficient EC cases. Positive hs-MSI scores were also detected in all 4 LS aspirates reported as complex hyperplasia. High hs-MSI was also present in 10 of 49 aspirates (20%) from LS carriers presenting a morphologically normal endometrium, where MMR protein expression loss was detected in 69% of the samples. Interestingly, the hs-MSI score was positively correlated with MMR-deficient gland density and the presence of MMR-deficient clusters, colocalizing PTEN and ARID1A expression loss. High hs-MSI scores and clonality were evidenced in 2 samples collected up to 4 months before EC diagnosis; hs-MSI scores increased over time in 5 LS carriers, whereas they decreased in a patient with endometrial hyperplasia after progestin therapy. In LS carriers, elevated hs-MSI scores were detected in aspirates from premalignant and malignant lesions and normal endometrium, correlating with MMR protein loss. hs-MSI assessment and MMR immunohistochemistry may help individualize EC risk assessment in women with LS.