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PURPOSE: The new CAP guideline published in August 2022 recommends using immunohistochemistry (IHC) to test for mismatch repair defects in gastroesophageal (GE), small bowel (SB), or endometrial carcinoma (EC) cancers over next-generation sequencing assessment of microsatellite instability (NGS-MSI) for immune checkpoint inhibitor (ICI) therapy eligibility and states there is a preference to use IHC over NGS-MSI in colorectal carcinoma (CRC). METHODS: We assessed the concordance of NGS-MSI and IHC-MMR from a very large cohort across the spectrum of solid tumors. RESULTS: Of the over 190,000 samples with both NGS-MSI and IHC-MMR about 1,160 were initially flagged as discordant. Of those samples initially flagged as discordant, 50.9% remained discordant after being reviewed by an additional pathologist. This resulted in a final discordance rate of 0.31% (590/191,767). Among CRC, GE, SB and EC, 55.4% of mismatch repair proficient/MSI high (MMRp/MSI-H) tumors had at least one somatic pathogenic mutation in an MMR gene or POLE. Mismatch repair deficient/microsatellite stable (MMRd/MSS) tumors had a significantly lower rate of high tumor mutational burden than MMRp/MSI-H tumors. Across all solid tumors, MMRd/MSI-H tumors had significantly longer overall survival (OS; hazard ratio [HR], 1.47, P < .001) and post-ICI survival (HR, 1.82, P < .001) as compared with MMRp/MSS tumors. The OS for the MMRd/MSS group was slightly worse compared to the MMRp/MSI-H tumors, but this difference was not statistically significant (HR, 0.73, P = .058), with a similar pattern when looking at post-ICI survival (HR, 0.43, P = .155). CONCLUSION: This study demonstrates that NGS-MSI is noninferior to IHC-MMR and can identify MSI-H tumors that IHC-MMR is unable to detect and conversely IHC-MMR can identify MMRd tumors that NGS-MSI misses.

BACKGROUND: Both defects in mismatch repair (dMMR) and high microsatellite instability (MSI-H) have been recognised as crucial biomarkers that guide treatment strategies and disease management in colorectal cancer (CRC). As MMR and MSI tests are being widely conducted, an increasing number of MSI-H tumours have been identified in CRCs with mismatch repair proficiency (pMMR). The objective of this study was to assess the clinical features of patients with pMMR/MSI-H CRC and elucidate the underlying molecular mechanism in these cases. METHODS: From January 2015 to December 2018, 1684 cases of pMMR and 401 dMMR CRCs were enrolled. Of those patients, 93 pMMR/MSI-H were identified. The clinical phenotypes and prognosis were analysed. Frozen and paraffin-embedded tissue were available in 35 patients with pMMR/MSI-H, for which comprehensive genomic and transcriptomic analyses were performed. FINDINGS: In comparison to pMMR/MSS CRCs, pMMR/MSI-H CRCs exhibited significantly less tumour progression and better long-term prognosis. The pMMR/MSI-H cohorts displayed a higher presence of CD8+ T cells and NK cells when compared to the pMMR/MSS group. Mutational signature analysis revealed that nearly all samples exhibited deficiencies in MMR genes, and we also identified deleterious mutations in MSH3-K383fs. INTERPRETATION: This study revealed pMMR/MSI-H CRC as a distinct subgroup within CRC, which manifests diverse clinicopathological features and long-term prognostic outcomes. Distinct features in the tumour immune-microenvironment were observed in pMMR/MSI-H CRCs. Pathogenic deleterious mutations in MSH3-K383fs were frequently detected, suggesting another potential biomarker for identifying MSI-H. FUNDING: This work was supported by the Science and Technology Commission of Shanghai Municipality (20DZ1100101).

The maintenance of DNA sequence integrity is critical to avoid accumulation of cancer-causing mutations. Inactivation of DNA Mismatch Repair (MMR) genes (e.g., MLH1 and MSH2) is common among many cancers, including colorectal cancer (CRC) and is the driver of classic microsatellite instability (MSI) in tumors. Somatic MSH3 alterations have been linked to a specific form of MSI called elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) that is associated with patient poor prognosis and elevated among African American (AA) rectal cancer patients. Genetic variants of MSH3 and their pathogenicity vary among different populations, such as among AA, which are not well-represented in publicly available databases. Targeted exome sequencing of MSH3 among AA CRC samples followed by computational bioinformatic pipeline and molecular dynamic simulation analysis approach confirmed six identified MSH3 variants (c.G1237A, c.C2759T, c.G1397A, c.G2926A, c.C3028T, c.G3241A) that corresponded to MSH3 amino-acid changes (p.E413K; p.S466N; p.S920F; p.E976K; p.H1010Y; p.E1081K). All identified MSH3 variants were non-synonymous, novel, pathogenic, and show loss or gain of hydrogen bonding, ionic bonding, hydrophobic bonding, and disulfide bonding and have a deleterious effect on the structure of MSH3 protein. Some variants were located within the ATPase site of MSH3, affecting ATP hydrolysis that is critical for MSH3's function. Other variants were in the MSH3-MSH2 interacting domain, important for MSH3's binding to MSH2. Overall, our data suggest that these variants among AA CRC patients affect the function of MSH3 making them pathogenic and likely contributing to the development or advancement of CRC among AA. Further clarifying functional studies will be necessary to fully understand the impact of these variants on MSH3 function and CRC development in AA patients.

Patients with Muir-Torre syndrome may have a systemic malignancy and a sebaceous neoplasm such as an adenoma, epithelioma, and/or carcinoma. The syndrome usually results from a germline mutation in one or more mismatch repair genes. Iatrogenic or acquired immunosuppression can promote the appearance of sebaceous tumors, either as an isolated event or as a feature of Muir-Torre syndrome and may unmask individuals genetically predisposed to the syndrome. Two iatrogenically immunosuppressed men with Muir-Torre syndrome features are described. Similar to these immunocompromised men, Muir-Torre syndrome-associated sebaceous neoplasms have occurred in solid organ transplant recipients, human immunodeficiency virus-infected individuals, and patients with chronic diseases who are treated with immunosuppressive agents. Muir-Torre syndrome-associated sebaceous neoplasms occur more frequently and earlier in kidney recipients, who are receiving more post-transplant immunosuppressive agents, than in liver recipients. The development of sebaceous neoplasms is decreased by replacing cyclosporine or tacrolimus with sirolimus or everolimus. Specific anti-cancer vaccines or checkpoint blockade immunotherapy may merit exploration for immune-interception of Muir-Torre syndrome-associated sebaceous neoplasms and syndrome-related visceral cancers. We suggest germline testing for genomic aberrations of mismatch repair genes should routinely be performed in all patients-both immunocompetent and immunosuppressed-who develop a Muir-Torre syndrome-associated sebaceous neoplasm.

Background: Microsatellite instability (MSI) is a well-established predictive biomarker for immune checkpoint inhibitor (ICI) response in metastatic colon cancer. Both high MSI and tumor mutational burden (TMB) are markers of genomic instability. However, the prognostic and predictive value of TMB in patients with microsatellite stable (MSS) tumors remains unclear. Methods: We evaluated the prognostic significance of TMB levels in MSS metastatic colon cancer patients undergoing standard treatments. Tumor responses were assessed using RECIST v1.1 criteria. Comprehensive clinical and molecular profiling was conducted, including next-generation sequencing (NGS) for TMB evaluation with the TruSight Oncology® kit. Overall survival (OS) was the primary endpoint. Multivariate Cox regression analysis was utilized to assess the relationship among potential prognostic factors. Results: Among 102 MSS metastatic colon cancer patients, high TMB (> 10 mut/mb) was associated with a significantly longer median OS compared to low TMB (70.0 vs 45.0 months, respectively; HR: 0.45; 95% CIs 0.21 to 0.96; P = 0.0396). Multivariate analysis, adjusting for age, gender, number of metastatic sites, response to first-line chemotherapy, RAS mutational status, and liver involvement, identified TMB as an independent prognostic factor, along with response to first-line chemotherapy. Conclusions: Our results highlight the prognostic significance of TMB in MSS metastatic colon cancer patients, suggesting its potential role in patient stratification and treatment decision-making. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the mutational landscape of colon cancer (CC) is crucial for targeted therapy development. Microsatellite instability (MSI-H), rat sarcoma (RAS), and B-Raf proto-oncogene, serine/threonine kinase (BRAF) mutations (MT) are pivotal markers. Further investigation into clinicopathological features of RAS and BRAF MT in microsatellite stable (MSS) and MSI-H tumors is warranted. Methods: A retrospective analysis of 4883 localized CC patients (pts.) was conducted. Molecular profiling assessed MSI, KRAS, NRAS, and BRAF MT. Correlation with clinicopathological data employed ANOVA and Chi-square tests. Disease-free survival (DFS) and overall survival (OS) were analyzed adjusting for age, gender, sidedness, UICC stage, Charlson Comorbidity Index (CCI). A Cox model incorporated all variables as covariates. Results: This analysis included 4883 pts. (2302 female/2572 male, 3865 (79.2%) MSS, 1018 (20.8%) MSI-H). MSS pts. had more All-Wild Type (WT), KRAS MT, and NRAS MT tumors vs. MSI-H pts. (42.1% vs. 21.1%; 39.8% vs. 15.4%; 3.6% vs. 0.7%; p<0.001 for each). BRAF MT tumors (95.5% BRAF V600E MT) were more prevalent in MSI-H individuals (62.8% vs. 8.1%, p<0.001). KRAS and BRAF MT tumors were more frequently right-sided, while BRAF MT tumors were associated with female gender, advanced disease stage, lymph node positivity, and poorer differentiation in the MSS subset (p<0.001). Common KRAS mutations included p.G12D (30.44%) and p.G12V (21.3%) in MSS and p.G13D (28.9%) and p.G12D (22.37%) in MSI-H. NRAS MT tumors were dominated by codon 61 mutations (51.7%). Survival analysis revealed worst prognosis in BRAF MT MSS tumors (DFS: HR 1.74 (95% CI 1.15-2.62, p=0.009; OS: HR 1.61 (95% CI 0.99-2.6), p=0.055). The 3-years DFS and 5-years OS rates were lowest in this subset (61.6% and 57.7% respectively). Discussion: These findings highlight the complex interplay between molecular subtypes, clinicopathological features, and survival outcomes in early CC. Further research is needed to elucidate underlying mechanisms and develop personalized treatment strategies. [ABSTRACT FROM AUTHOR]

Simple Summary: Tumours of the colon and endometrium (lining of the womb) often have defects in genes that repair our DNA. Identifying these tumours is important for patient treatment and identifying Lynch syndrome (LS), an inherited cancer predisposition. However, the two methods most commonly used to identify these defects often give inconsistent results for endometrial tumours. Here, we investigate these inconsistencies by re-analysing 361 tumour samples from clinical trials with a third assay and establish that they are largely due to false positives in one assay (immunohistochemistry) and false negatives in the other (Promega MSI assay). In addition, the DNA repair defects seem to have a reduced impact within endometrial tumours. However, we find that tumours with defects in a gene called MSH6, especially when associated with LS, are only detected efficiently with immunohistochemistry. This supports current guidelines specifically recommending the use of this method for endometrial tumours. Background/Objectives: Mismatch repair (MMR) deficiency can be indicative of Lynch syndrome (LS) and guide treatment with immune checkpoint inhibitors. Colorectal cancers (CRCs) and endometrial cancers (ECs) are routinely screened to identify LS, primarily using immunohistochemistry (IHC) or microsatellite instability (MSI) testing, but concordance between these methods is variable in ECs. Here, we investigate this variability in 361 ECs from the Ohio OCCPI/OPTEC (n = 196) and Manchester PETALS (n = 165) trials, where concordance between assays differed significantly. Methods: Samples were re-tested using the amplicon-sequencing-based Newcastle MSI assay (NCL_MSI), and analysed with respect to existing IHC, MSI and MLH1 promoter hypermethylation data. Results: NCL_MSI showed consistency with the Ohio results (94% and 97% concordance with IHC and original MSI assays, respectively) and increased concordance within the Manchester cohort from 78% to 86% (MSI) and 84% (IHC). Among discordant Manchester samples, NCL_MSI was significantly associated with MLH1 promoter methylation status (p = 0.0028) and had the highest concordance with methylation, (62/69 samples, 90%), indicating utility as a screening tool in this tumour type. However, tumours with germline MSH6 defects were only detected efficiently with IHC; seven out of eight LS tumours classified as MSS by either MSI assay had isolated MSH6 loss, compared to four out of twelve classified as MSI-H by both (p = 0.028). Furthermore, reduced MSI signal was observed in tumours with isolated MSH6 loss (p = 0.009 Ohio, p = 6.2 × 10−5 Manchester) and in both ECs and CRCs with germline defects, although this only reached significance in CRCs (p = 0.002). Conclusions: These results provide further evidence that ECs with MSH6 loss in particular and LS tumours in general have an attenuated MSI signal, providing support for current guidelines specifically recommending IHC for LS detection and immune checkpoint therapy assessment in EC. [ABSTRACT FROM AUTHOR]

Colorectal cancer is one of the most common cancers and a frequent cause of mortality and morbidity. In this study, we aimed to investigate the Mismatch Repair (MMR) gene products of colorectal adenocarcinomas by immunohistochemistry, to investigate the relationship between deficiency in MMR and clinicopathologic, histomorphologic, and molecular features, and to elucidate the carcinogenesis of colorectal carcinomas in our region. Our study included 224 cases diagnosed with colorectal carcinoma; at Dicle University, Faculty of Medicine, Department of Pathology, between 2008 and 2022. Primary antibodies MLH1, MSH2, MSH6, and PMS2 were used in the immunohistochemical study. In our study, a significant relationship was found between deficiency in MMR and tumour location, tumour size, distant metastasis, stromal ratio, and desmoplasia. As a result, we found that deficiency in MMR is generally associated with good prognostic features, but this may not be the case in all cases and may be influenced by some geographical characteristics. [ABSTRACT FROM AUTHOR]

Patients with recurrent or metastatic endometrial cancer (EC) have poor prognoses with limited therapeutic options following immunotherapy or immunochemotherapy treatments. Inhibitors of KRAS mutations (KRAS-mut) have shown efficacy in early solid tumor studies, but data in EC are lacking. This study describes the frequency of KRAS-mut relative to other oncogenic alterations in EC to identify genomic characteristics of KRAS-mut tumors that could lead to novel therapeutic options. A molecular database of 7870 ECs was queried for presence of oncogenic mutations and immunotherapy biomarkers. Comparisons were performed using Fisher-Exact/ChiSquare (p -values) and adjusted for multiple tests by Benjamini-Hochberg (q) and pairwise nonparametric analysis using Wilcoxon Method. KRAS- mut is a relatively frequent genotype in EC, detected in 16% of cases. Codon 12 was most frequently mutated, with G12D (31%) and G12V (27%) the most common subtypes. Biomarkers of immunotherapy response co-occur with KRAS- mut. Microsatellite instability-high and tumor mutational burden-high status were observed in 34.1% and 36.5% in KRAS- mut compared to 19.8% and 16.9% in KRAS- WT, respectively (p < 0.05). PD-L1 >1% was detected in 8.4% vs 6.4% of KRAS-mut vs KRAS-WT (p < 0.05). BRCA1/2 mutations were detected with similar low frequency (5.9% vs 4.9%) among KRAS- mut and KRAS- WT ECs (p > 0.05). KRAS-mut was inversely associated with Her-2 overexpression (1.8% KRAS-mut vs 13% KRAS-WT. (p < 0.001). KRAS- mut represents a genotypically distinct group of ECs. Overlap exists with genomic predictors (TMB-high, MSI-high) of immunotherapy response, suggesting a possible biomarker-driven combination option with immunotherapy. Clinical trials to evaluate these strategies should be developed. • KRAS- mutated tumors represent a genotypically distinct group of ECs and occur in 16% of cases. • KRAS -mutated ECs are associated with longer overall mean survival compared to KRAS-WT ECs. • Overlaps with predictors of immunotherapy response suggest a possible biomarker-driven combination option. [ABSTRACT FROM AUTHOR]

Metastatic castration-resistant prostate cancer (mCRPC) typically exhibits resistance to immune checkpoint inhibitors (ICIs). However, a subset of mCRPC patients displays a more immunogenic profile. This study examines efficacy and safety of dual ICI therapy in molecularly selected mCRPC. This single-arm, phase II trial included 69 molecularly selected mCRPC patients with mismatch repair deficiency (dMMR), non-synonymous tumour mutational burden ≥7.1 muts/Mb (hTMB), a BRCA2 mutation (BRCAm), or biallelic CDK12 inactivation (CDK12i). Efficacy was assessed in ICI-naïve patients (cohort A) with RECIST 1.1 (A1) and Prostate Cancer Working Group 3 (A2) measurable disease. Safety was evaluated in cohorts A and B (prior ICI monotherapy). Treatment included nivolumab 3 mg/kg and ipilimumab 1 mg/kg every 3 weeks for four cycles, followed by nivolumab 480 mg every 4 weeks for up to 1 year. The primary endpoint was disease control rate beyond 6 months (DCR > 6), aiming to surpass a DCR > 6 of 22%. Patients initiated treatment between January 2021 and February 2024. Cohort A included 65 patients. Of these, 21 had dMMR (32%), 8 had hTMB (12%), 20 had BRCAm (31%), and 16 had CDK12i (25%). DCR > 6 was achieved in 38% of patients [95% confidence interval (CI) 27% to 51%], and was highest in dMMR (81%), followed by hTMB (25%), CDK12i (19%), and BRCAm (15%). Objective response rate in cohort A was 38% (95% CI 22% to 55%) and 47% (95% CI 34% to 60%) exhibited a 50% decline in prostate-specific antigen levels. Median progression-free survival (PFS) was 4.0 months (95% CI 3.5-12.0 months) in cohort A, and 32.7 months (95% CI 21.8 months-not reached) in dMMR patients. Treatment-related adverse events (TRAEs) led to permanent discontinuation in 14 of 69 patients (20%). Grade ≥3 TRAEs occurred in 48% of patients, with diarrhoea and elevated transaminases each in 10%. There was one treatment-related death due to a bowel perforation and a second following euthanasia after grade 4 toxicity. This trial of dual ICIs in molecularly selected mCRPC met its primary endpoint, showing DCR > 6 in 38% of patients. Dual ICIs exhibited modest responses in the hTMB, BRCAm, and CDK12i subgroups, but demonstrated exceptional efficacy in dMMR. • Ipilimumab and nivolumab induced a 6-month DCR of 38% in patients with molecularly selected mCRPC. • Durable benefit was particularly high in patients with dMMR who demonstrated a median PFS of 32.7 months. • PFS was shorter in patients receiving prior taxanes, suggesting that dual ICIs should be initiated early in the disease course. [ABSTRACT FROM AUTHOR]

Background: Cutaneous melanoma (CM) is the most common type in Caucasians, while acral melanoma (AM) and mucosal melanoma (MM), which are resistant to immunotherapies and BRAF/MEK-targeted therapies, are more common in East Asians. Genomic profiling is essential for treating melanomas, but such data are lacking in Japan. Methods: Comprehensive genomic profiling data compiled in the Center for Cancer Genomics and Advanced Therapeutics (C-CAT) were analyzed. Results: A total of 380 melanomas was analyzed, including 136 CM, 46 AM, 168 MM, and 30 uveal melanoma (UM). MM included conjunctival, sinonasal, oral, esophageal, anorectal, and vulvovaginal melanomas. No significant difference in the median tumor mutational burden (TMB) of CM (3.39 mutations/megabase), AM (2.76), and MM (3.78) was the key finding. Microsatellite instability-high status was found in one case. BRAF V600E/K was found in only 45 patients (12%). Key driver mutations in CM were BRAF (38%), NRAS (21%), NF1 (8%), and KIT (10%), with frequent copy number alterations (CNAs) of CDKN2A, CDKN2B, and MYC. AM was characterized by altered KIT (30%), NRAS (26%), and NF1 (11%) and CDKN2A, CDKN2B, CDK4, MDM2, and CCND1 CNAs. MM was characterized by altered NRAS (24%), KIT (21%), and NF1 (17%) and MYC, KIT, and CDKN2A CNAs, with differences based on anatomical locations. UM bore GNAQ or GNA11 driver mutations (87%) and frequent mutations in SF3B1 or BAP1. Conclusion: The distinct genomic profiling in Japanese patients, including lower TMB, compared to Caucasians, is associated with poorer treatment outcomes. This result underscores the need for more effective therapeutic agents. [ABSTRACT FROM AUTHOR]

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Background: Mismatch repair deficient (dMMR) gastroesophageal cancers (GEC) are a distinct subgroup. Among patients with locally advanced disease, previous trial data suggest a good response to neoadjuvant immune checkpoint inhibitors (nICI). Patients and Methods: Since 2019, our institution has routinely performed MMR testing for new GEC cases. Patients diagnosed with GEC (2019–2024) were included in the study. Quantitative data are described as the median and interquartile range (IQR); qualitative data are described as quantities and percentages. Results: A total of 24 patients with dMMR GEC were identified following implementation of routine immunohistochemical testing; 14 were potentially resectable with a median follow-up of 14 months (IQR 8–27). All patients underwent pre-treatment positron emission tomography (PET; median SUV 20.9). Among the 14 potentially resectable patients, 4 underwent immediate surgery, 10 were treated with nICI, and 5 underwent surgical resection to date. All regimens included PD-1 inhibitors, with 70% receiving pembrolizumab. Re-staging PET was performed in five patients; the median post-nICI SUV was 5.1 (range 4.7–6.3). All resected specimens had gross ulceration after nICI, but 60% (N = 3) had a pathologic complete response (pCR) following nICI; one patient had a near-complete response (nCR) and one patient had a partial response (pPR). Reduction in SUV was 75% and 82% in the pCR patients, 25% in the nCR patient, and 43% in the pPR patient. Conclusions: dMMR GECs are responsive to nICI in this limited experience, mirroring early clinical trial data. Given persistent metabolic activity and visible ulceration despite pCR, studies should continue to optimize tools for estimating post-nICI pCR in these patients. [ABSTRACT FROM AUTHOR]

ABSTRACT Background Methods Results Conclusion Microsatellite instability (MSI) has prognostic value and impacts therapy strategies in several malignancies. Data regarding MSI in melanoma are scarce. The aim of this study was to assess MSI through the analysis of MMR protein expression in patients with melanoma.An observational retrospective single‐center study was designed based on patients with primary melanoma. We assessed MSI through immunohistochemical staining with anti‐MLH1, anti‐MSH2, anti‐MSH6, and anti‐PMS2 on full–thickness excision tissue.Ninety‐three patients were included in this study. The complete absence of nuclear staining in tumoral cells was extremely rare, with only one melanoma not expressing MSH6. Most melanomas showed an expression index for MLH1 (77.7%), MSH2 (87.2%), and PMS2 (78.6%) ≥ 75%. Most melanomas (57.8%) exhibited an MSH6 expression index in the range of 1%–74%. A low MSH6 expression index and a reduced combined MMR protein expression index (MMR‐e) were significantly associated with higher melanoma‐specific survival. A mild PMS2 staining intensity was significantly associated with a higher melanoma‐specific survival. The patients with high MMR‐e who received immunotherapy progressed and died more frequently than those with reduced MMR‐e (75% vs. 33.3%).More studies are needed to further define the role of MSI in melanoma prognosis and response to immunotherapy. [ABSTRACT FROM AUTHOR]

Microsatellite instability-high (MSI-H) gastric cancer (GC) exhibits high tumor-infiltrating lymphocyte (TIL) density. Despite the recognized significance of the immune microenvironment in MSI-H GC, our understanding of TIL remains limited. This study aimed to investigate the clinicopathologic and prognostic implications of T cell subsets in MSI-H GC. Single immunohistochemistry (IHC) for CD8, TCF1, and CD103, and double IHC for CD8/TCF1 and CD8/CD103 were performed in 382 surgically resected MSI-H GC samples. Densities of single or double positive immune cells were quantified and correlated with clinicopathologic features and overall survival (OS). TCF1 + cell densities showed weak correlations with CD8 + and CD103 + cell densities, while CD8+/TCF1 + cell density moderately correlated with CD8+/CD103 + cell density (R2 = 0.539, p < 0.001). Single IHC analyses showed no significant associations between CD8+, TCF1+, or CD103 + cell densities and OS (p > 0.05). Notably, elevated CD8+/TCF1 + cell density and a high CD8+/TCF1 + to CD8 + ratio correlated with less aggressive clinicopathologic features and improved OS (p = 0.017 and 0.001, respectively). Multivariable Cox-regression identified CD8+/TCF1 + to CD8 + ratio as an independent prognostic factor (p = 0.028). We demonstrated the prognostic significance of CD8+/TCF1 + to CD8 + ratio using double IHC in a large cohort of MSI-H GC. [ABSTRACT FROM AUTHOR]

Background: Colorectal cancer (CRC) is a leading cause of cancer-related mortality, highlighting the necessity for multifaceted treatment strategies, including preoperative treatment (PT), which can enhance surgical outcomes and provide prognostic insights. This study aims to clarify the impact of PT-induced changes in mismatch repair (MMR) and human epidermal growth factor receptor 2 (HER2) expression, potentially informing tailored treatment strategies and improving clinical outcomes for CRC patients. Methods: This retrospective study analyzed 120 paired samples from CRC patients who underwent preoperative treatment, comparing pre- and post-treatment specimens. A control group of 60 untreated surgical specimens was also included. Immunohistochemistry assessed MMR proteins (MSH6, MSH2, MLH1, PMS2) and HER2 expression. MSI status was determined in samples with low MMR expression. Results: Compared to pre-treatment samples, post-treatment samples exhibited lower levels of MSH6, MSH2, and total MMR expression, along with higher levels of HER2 expression. However, when compared to the untreated control group, there were no significant differences in the expression of MSH6, total MMR, and HER2. All samples that exhibited weak MMR expression and those that shifted to deficient mismatch repair (dMMR) status following treatment had stable microsatellite status. No clear clinicopathological characteristics or prognostic factors were found to be associated with changes in MMR and HER2 expression, except for the use of fluorouracil or capecitabine, which was related to changes in total MMR scores. ypTNM stage and TRG scores were identified as independent factors affecting disease progression in our study. Conclusions: PT is associated with a reduction in MMR expression, notably for the MSH2 protein, while it does not appear to influence HER2 expression. [ABSTRACT FROM AUTHOR]

To evaluate different Lynch syndrome (LS) screening approaches and establish an efficient and sensitive strategy are critical for clinical practice. In total, 583 patients with colorectal carcinoma (CRC) at Fudan University Shanghai Cancer Center were enrolled. Patient samples were examined by immunohistochemistry (IHC) and next‐generation sequencing (NGS), and MLH1 promoter hypermethylation (MPH) was detected in MLH1‐deficient cases. Germline genetic testing was performed in cases with deleterious variants and large genomic rearrangements (LGRs) of tumor MMR genes were detected in cases with dMMR or MSI‐H cases with no MMR germline variants. Our results showed that triage with IHC and followed by BRAF/MLH1 methylation testing (Strategy 1) identified 93.3% (70/75) of LS cases. IHC followed by germline NGS (Strategy 2) or direct tumor NGS (Strategy 3) both identified 98.7% (74/75) of LS cases. The proportion of LGRs in LS cases was 16.0% (12/75), while 84.0% (63/75) showed SNV/Indel. The average cost per patient was ¥6010.81, ¥6058.48, and ¥8029.98 for Strategy 1, Strategy 2 and Strategy 3, respectively. The average time spent on different strategies was 4.74 days (Strategy 1), 4.89 days (Strategy 2), and 14.50 days (Strategy 3) per patient, respectively. LS and Lynch‐like syndrome (LLS) were associated with an earlier onset age than MPH. In conclusion, we compared different workflows for LS screening and IHC plus germline NGS is recommended for LS screening when taking sensitivity, time, and cost into account. Moreover, multiplex ligation‐dependent probe amplification made up for the shortcoming of NGS and should be incorporated into routine screening. [ABSTRACT FROM AUTHOR]

The incidence of Early-Onset Colorectal Cancer (EOCRC) is increasing. However, the prognosis of EOCRC compared to Late-Onset Colorectal Cancer (LOCRC), and the ideal age for initial colorectal cancer (CRC) screening are not clear. In this study, we identified the pathological differences between the groups and determined the optimal screening age for CRC patients. We included 10,172 patients diagnosed with CRC from January 2011 to December 2021 in this study. Survival differences were compared by plotting Kaplan–Meier survival curves and conducting landmark analysis. Additionally, the diagnostic age of CRC patients was analyzed using age cumulative curves. Compared to LOCRC patients, EOCRC patients had a higher proportion of deficient mismatch repair (dMMR) and more advanced TNM staging (P < 0.05). The five-year survival of EOCRC patients was significantly better than that of LOCRC patients (P < 0.05). Laparoscopic surgery improved the long-term survival of EOCRC patients. Proficient mismatch repair (pMMR) favored the long-term survival of EOCRC patients. The survival rate of EOCRC patients at TNM stages I and II was higher than that of LOCRC patients at the same stages (P < 0.05). The age cumulative curve showed a substantial increase in the number of CRC patients at 40 years. The long-term prognosis of EOCRC patients is better than that of LOCRC patients, especially among those with pMMR, stages I–II, and who undergo laparoscopic surgery. For people with a high risk of cancer, such as a family history of cancer and poor lifestyle habits, the starting age for CRC screening should be 40 years. [ABSTRACT FROM AUTHOR]