MMR Protein Research Articles

Recommandations pour la pratique clinique Nice/Saint-Paul-de-Vence 2022–2023 : Diagnostic histomoléculaire des carcinomes de l'endomètre

French recommendations for clinical practice Nice-Saint-Paul de Vence 2022-2023: histomolecular diagnosis of endometrial carcinomas The characterisation of endometrial carcinomas has been recently modified and enriched by molecular classification, the integration of which now impacts therapeutic decisions on whether adjuvant therapy should be administered or not in localized tumors, and influences treatment selection in advanced disease. Mandatory information includes histological type according to WHO 2020 classification, histological grade, hormone receptors status and molecular classification, the main new elements to provide being analysis of MMR proteins, p53 status and POLE status in selected cases. Sampling and preparation of material must be performed adequately to allow complete analysis. Numerous markers can be used to better define histological type, distinguish between primary lesion or metastases, or provide prognostic information. Determination of MMR/MSI profile is complex but well defined by guidelines that precisely describe techniques to be used and interpretation rules. Knowledge of POLE status is useful to guide therapeutic strategy, especially to consider de-escalation in stages I and II, in particular in case of high grade and/or p53 mutated tumors. This is why indications of POLE determination must be well defined. Finally, oncogenetics consultation is recommended in dMMR tumors (except in case or MLH1 promoter methylation) and in patients with evocative familial history.

Clinicopathological characteristics of endometrial carcinomas according to DNA mismatch repair protein status

DNA mismatch repair protein deficiency (MMRd) in endometrial carcinoma is associated with the risk of Lynch syndrome and response to immune checkpoint inhibitors. It is also related to microsatellite instability and corresponds to a molecular subtype of endometrial tumor with an unclear prognosis. Here, we evaluated the clinicopathological characteristics and prognosis of 312 consecutive endometrial carcinoma cases submitted to complete surgical staging at a single institution. We compared MMRd and mismatch repair protein–proficient (MMRp) tumors and examined the effects of the MMR protein loss type (MLH1/PMS2 vs. MSH2/MSH6) and influence of L1CAM and p53 expression. The median follow-up period was 54.5 (range, 0–120.5) months. No difference was observed between MMRd [n = 166 (37.2%)] and MMRp [n = 196 (62.8%)] cases in terms of age, body mass index, FIGO stage, tumor grade, tumor size, depth of myometrial infiltration, or lymph node metastasis. More MMRd than MMRp tumors had endometrioid histology (87.9% vs. 75.5%) and despite MMRd had more lymphovascular space invasion (LVSI; 27.2% vs. 16.9%), they presented fewer recurrences and no difference in lymph node metastasis and disease-related death. Relative to those with MLH1/MSH6 loss, tumors with MSH2/MSH6 loss were diagnosed at earlier FIGO stages, were smaller, and had less ≥50% myometrial invasion, LVSI and lymph node metastasis. Outcomes, however, did not differ between these groups. L1CAM positivity and mutation-type p53 expression were more common in MMRp than in MMRd tumors and did not differ between the MLH1/PMS2 and MSH2/MSH6 loss groups. In the entire cohort, L1CAM and mutation p53 expression were associated with worse prognosis, but only non-endometrioid histology, FIGO stage III/IV, and deep myometrial infiltration were significant predictors. In the subgroup of endometrioid carcinomas, only FIGO stage III/IV was associated with poor outcomes. The risk of lymph node metastasis was associated with tumor size, non-endometrioid histology, and multifocal LVSI. For MMRd tumors, only tumor size and myometrial invasion depth were predictive of lymph node involvement. In our cohort, MMRd tumors were associated with greater recurrence-free, but not overall, survival. The precise identification of MMRd status, present in a substantial proportion of endometrial cancer cases, is a challenge to be overcome for proper patient management. MMRd status serves as a marker for Lynch syndrome, and a significant number of these tumors are high risk and candidate to immunotherapy.

Mismatch repair deficiency and microsatellite instability-high in urothelial carcinoma: A systematic review and meta-analysis.

4570 Background: Mismatch repair deficiency (dMMR) and microsatellite instability-high (MSI-H) occur in a small subset of urothelial carcinoma (UC) and confer a sensitivity to immunotherapy in multiple solid tumors. Due to the rarity of this patient subset in UC, there is a lack of prospective data on their prevalence or of clinical outcomes with immunotherapy and other treatment modalities. Methods: We performed a systematic review with the objectives of estimating the prevalence of dMMR and MSI-H in urothelial bladder cancer (BC) and upper tract urothelial carcinoma (UTUC) apart from estimating survival and clinical outcomes of treatment. We searched for published prospective and retrospective studies, review articles, case reports, case series, conference proceedings, letters, commentaries, and editorials on dMMR and MSI-H in BC and UTUC published up to 10/26/2022 in PubMed, Cochrane CENTRAL, Embase and Web of Science: Core Collection databases. The study protocol is registered on the PROSPERO database (CRD42022365690). Prevalence data were analyzed using meta-analysis with random-effects models and are reported here. Results: A total of 1,750 studies were screened, of which 125 were included. Thirty-six studies (including 5,113 patients) reported frequencies of dMMR, and 42 studies (including 21,291 patients) reported on MSI-H. Of the total included patients, sex was reported in 11,225, with 72.6% being male and 27.4% female. Age ranged from 17-97 years. Reported primary site was BC in 64.4%, UTUC in 16.3% and not stated in 19.3%. Disease stage reported in 5,341 patients was M0 in 75.0% and M1 in 25.0%. Of the M0 patients, tumor stage data were available in 3,149 patients: Ta-T1 in 33.6% and T2-T4 in 66.4%. The pooled weighted prevalence of dMMR in UC patients was 6% (95% CI 5-8%). The breakdown for BC and UTUC were 2% (95% CI 1-3%) and 9% (95% CI 7-12%), respectively. The three most frequent MMR protein loss patterns in UC, BC and UTUC are shown in the table. Out of 42 studies reporting MSI status, 21 used polymerase chain reaction (PCR) and 21 used next-generation sequencing (NGS). Pooled weighted prevalence of MSI-H in UC was 3% (95% CI 2-3%). In BC, the prevalence was 1% (95% CI 1-1%) and in UTUC, it was 11% (95% CI 8-13%). Conclusions: dMMR and MSI-H were observed more frequently in UTUC than BC. Further analysis on survival and clinical outcomes of dMMR/MSI-H UC with different treatment modalities is ongoing. Additionally, clinical trials in dMMR and/or MSI-H UC are in development to study immunotherapeutic strategies to improve outcomes in both early and advanced stages for this small but important subset of patients. [Table: see text]

The differential response to immune checkpoint inhibitors (ICIs) according to mismatch repair alterations in gastrointestinal (GI) non-colorectal cancers (non-CRCs) and the impact of dual vs. monotherapy ICIs on survival in GI (CRC and non-CRC) cancers.

2620 Background: In patients with mismatch repair deficient (dMMR) colorectal cancers (CRCs), we previously reported that loss of expression of MSH2 and MSH6 (MutS co-loss) was associated with better response to ICIs and longer median overall survival (mOS) compared to loss of expression of MLH1 and PMS2 (MutL co-loss). Here, we expanded our analysis and included gastrointestinal (GI) non-CRCs and explored the impact of dual vs. monotherapy ICIs on mOS in GI (CRC and non-CRC) cancers. Methods: Specimens were profiled by next-generation sequencing (592, NextSeq; WES, WTS NovaSeq) (Caris Life Sciences, Phoenix, AZ). MMR/microsatellite instability (MSI) status was determined by immunohistochemistry (IHC) of MMR protein. Real world OS was extracted from insurance claims and calculated using Kaplan-Meier estimates for molecularly defined cohorts from first treatment with ICIs (Nivolumab, Nivo; Ipilumumab, ipi; or Pembrolizumab, pembro) to last contact. Statistical significance was determined using chi-square and Mann-Whitney U test with p-values adjusted for multiple comparisons (q < 0.05). Results: The GI non-CRC cohort (N= 19,767) included cancers of the esophagus, stomach, gastroesophageal junction, pancreas, bile duct and small bowel with 97 (0.49%) patients having MutS co-loss, and 494 (4.03%) patients having MutL co-loss. MutS co-loss was associated with increased KRAS (45.4% vs 25.2%, q<0.01), CDKN2A (29.2% vs 9.0%), GNAS (27.8% vs 7.8%) and SMAD4 (17.5% vs 5.9%) mutations compared to MutL co-loss. Independent of treatment, MutS co-loss (N=74) had improved mOS compared to MutL co-loss (N=332) (40.4 m vs. 26.2 m, HR = 0.66; (95% CI: 0.46-0.95), P=0.024). In patients treated with ICIs, the mOS in MutS co-loss (N=21) was better compared to MutL co-loss (N=76) (not reached (NR) vs. 25.4 m, HR= 0.23 (95% CI: 0.07-0.75), p=0.008). At 3 years, more than 80% of the patients with MutS co-loss were alive. Of particular importance, when looking at all GI (CRC and non-CRC) patients, the mOS of MutL co-loss treated with ipi/nivo (N=18) trended for better mOS compared to MutL co-loss treated with pembro (N=215) (NR vs. 28.2m (HR=0.39; (95% CI:0.14-1.07), p=0.057), while the mOS of MutS co-loss treated with ipi/nivo (N=6) was not different compared to MutS co-loss treated with pembro (N=44) (NR vs. NR, HR=0.75 (95% CI: 0.094-5.92), p=0.78). Conclusions: In ICI-treated GI non-CRCs, the mOS was longer in MutS co-loss compared to MutL co-loss. In ICI-treated GI (CRC and non-CRC) patients with MutL co-loss, there was a trend for better survival with ipi/nivo compared to pembro. Our data suggest that the MutS vs. MutL status may guide the choice of ICIs regimen (Dual vs. Monotherapy) but more data are needed.

Microsatellite instability in non-endometrioid ovarian epithelial tumors: a study of 400 cases comparing immunohistochemistry, PCR, and NGS based testing with mutation status of MMR genes

Testing of microsatellite instability is not only used as a triage for possible Lynch syndrome, but also to predict immunotherapy treatment response. The aim of this study was to assess the frequency of mismatch repair deficiency (MMR-D) / microsatellite instability (MSI) in 400 cases of non-endometrioid ovarian tumors (high-grade serous, low-grade serous, mucinous and clear cell), to compare different methodological approaches of testing, and to assess the optimal approach for next generation sequencing (NGS) MSI testing. For all tumors, we evaluated immunohistochemical (IHC) expression of MMR proteins and assessed microsatellite markers by PCR-based method. Except for high-grade serous carcinoma, we correlated the findings of IHC and PCR with NGS-based MSI testing. We compared the results with somatic and germline mutation in MMR genes. Among the whole cohort, seven MMR-D cases, all clear cell carcinomas (CCC), were found. On PCR analysis, six cases were MSI-high and one was MSS. In all cases, mutation of an MMR gene was found; in two cases, the mutation was germline (Lynch syndrome). An additional five cases with a mutation in MMR gene(s) with MSS status and without MMR-D were identified. We further utilized sequence capture NGS for MSI testing. Employing 53 microsatellite loci provided high sensitivity and specificity. Our study shows that MSI occurs in 7% of CCC while it is rare or absent in other non-endometrioid ovarian neoplasms. Lynch syndrome was present in 2% of patients with CCC. However, some cases with MSH6 mutation can evade all testing methods, including IHC, PCR, and NGS-MSI.

Investigation of the Relationship Between Immunohistochemical Mismatch Repair (MMR) Protein Expression and Prognostic Parameters in Endometrial Carcinomas

Objective: Molecular classification has been the most important development in endometrial carcinomas in recent years. This classification divides tumors into four groups: (i) POLE mutant group, (ii) microsatellite instable (MSI) group, (iii) high copy number group (P53 mutation), and (iv) low copy number group. Among these groups, POLE and MSI groups stand out with their better prognosis and potential to benefit from immune-control inhibitor therapy. In our study, we aimed to compare the prognostic parameters of patients with and without nuclear expression loss in MMR proteins (MLH-1, PMS-2, MSH-2, MSH-6) by immunohistochemical (IHC) method. Methods: Between 2017 and 2020, 80 patients who were diagnosed with endometrial carcinoma in hysterectomy material and whose MMR proteins were evaluated as IHC were included in the study. Patients with and without MMR loss were compared in terms of tumor size, histological grade (HD), depth of myometrial invasion, lymphovascular invasion (LVI), and cervical involvement. Results: Loss of any of the MMR proteins was present in 37 cases (46.3%), while 43 cases (53.7%) had no loss. When the cases were compared in terms of loss of MMR protein nuclear expression, 45.9% (17/37) of the cases with loss and 27.9% (12/43) of the cases without loss had histologic grade III (P = 0.03). There was no statistically significant difference between the two groups in terms of myometrium 1/2 external invasion, cervical stromal involvement, and LVI. Conclusion: Approximately half of the patients in our study lost at least one of the MMR proteins. The most common losses were MLH-1 and PMS-2. The HD of patients with loss of nuclear expression of MMR proteins tended to be statistically significantly higher than those without loss.

In vitro and ex vivo proteomics of Mycobacterium marinum biofilms and the development of biofilm-binding synthetic nanobodies.

The antibiotic-tolerant biofilms present in tuberculous granulomas add an additional layer of complexity when treating mycobacterial infections, including tuberculosis (TB). For a more efficient treatment of TB, the biofilm forms of mycobacteria warrant specific attention. Here, we used Mycobacterium marinum (Mmr) as a biofilm-forming model to identify the abundant proteins covering the biofilm surface. We used biotinylation/streptavidin-based proteomics on the proteins exposed at the Mmr biofilm matrices in vitro to identify 448 proteins and ex vivo proteomics to detect 91 Mmr proteins from the mycobacterial granulomas isolated from adult zebrafish. In vitro and ex vivo proteomics data are available via ProteomeXchange with identifiers PXD033425 and PXD039416, respectively. Data comparisons pinpointed the molecular chaperone GroEL2 as the most abundant Mmr protein within the in vitro and ex vivo proteomes, while its paralog, GroEL1, with a known role in biofilm formation, was detected with slightly lower intensity values. To validate the surface exposure of these targets, we created in-house synthetic nanobodies (sybodies) against the two chaperones and identified sybodies that bind the mycobacterial biofilms in vitro and those present in ex vivo granulomas. Taken together, the present study reports a proof-of-concept showing that surface proteomics in vitro and ex vivo proteomics combined is a valuable strategy to identify surface-exposed proteins on the mycobacterial biofilm. Biofilm surface-binding nanobodies could be eventually used as homing agents to deliver biofilm-targeting treatments to the sites of persistent biofilm infection. IMPORTANCE With the currently available antibiotics, the treatment of TB takes months. The slow response to treatment is caused by antibiotic tolerance, which is especially common among bacteria that form biofilms. Such biofilms are composed of bacterial cells surrounded by the extracellular matrix. Both the matrix and the dormant lifestyle of the bacterial cells are thought to hinder the efficacy of antibiotics. To be able to develop faster-acting treatments against TB, the biofilm forms of mycobacteria deserve specific attention. In this work, we characterize the protein composition of Mmr biofilms in bacterial cultures and in mycobacteria extracted from infected adult zebrafish. We identify abundant surface-exposed targets and develop the first sybodies that bind to mycobacterial biofilms. As nanobodies can be linked to other therapeutic compounds, in the future, they can provide means to target therapies to biofilms.

Microsatellite Instability and P53 Aberrant Expression in Gastric Adenocarcinoma: Immunohistochemical Assessment and Correlation with Clinico-pathological Characteristics

Background: Gastric cancer (GC) is among the five most frequent cancer worldwide, following lung, breast, colorectal, and prostate cancer. It is the 12th most prevalent cancer in both sexes in Egypt, accounting for 1.6% of all malignancies. Distinct molecular subtypes of gastric adenocarcinoma (e.g., microsatellite instable subtype and P53 aberrant subtype) have been reported by different classification systems. However, the relation of these molecular subtypes to different clinicopathological features is still controversial.
 Aim of the Work: To utilize the immunohistochemical expression of DNA MMR proteins (MLH1 and MSH2) and p53 to detect microsatellite unstable and P53 aberrant molecular types in gastric adenocarcinoma. Moreover, to correlate immunohistochemically detected microsatellite unstable and P53 aberrant molecular types of gastric carcinoma with different clinicopathological characteristics.
 Materials and Methods: The immunohistochemical expression of MLH1, MSH2 and P53 proteins was evaluated in 70 cases of gastric adenocarcinoma.
 Results: Microsatellite status/Mismatch repair status showed a statistically significant relation with WHO classification, tumor differentiation, lymph node status, and TNM staging. P53 aberrant type showed a statistically significant relation with tumor differentiation, depth of tumor invasion, lymph node status, and TNM staging.
 Conclusions and Recommendations: Microsatellite instable GC and P53 aberrant GC are two distinct molecular subtypes of gastric adenocarcinoma with distinct clinicopathological features and different prognostic outcomes. Microsatellite instable tumors are associated with good prognostic parameters while, P53 aberrant tumors are associated with poor prognostic parameters. Both subtypes could be detected using immunohistochemistry and could represent potential targets for future therapeutic agents.

Prevalence and Clinical Implications of Mismatch Repair-Proficient Colorectal Cancer in Patients With Lynch Syndrome.

Lynch syndrome (LS)-associated colorectal cancer (CRC) is characterized by mismatch repair-deficiency (MMR-D) and/or microsatellite instability (MSI). However, with increasing utilization of germline testing, MMR-proficient (MMR-P) and/or microsatellite stable (MSS) CRC has also been observed. We sought to characterize MMR-P/MSS CRC among patients with LS. Patients with solid tumors with germline MMR pathogenic/likely pathogenic (P/LP) variants were identified on a prospective matched tumor-normal next-generation sequencing (NGS) protocol. CRCs were evaluated for MMR-D via immunohistochemical (IHC) staining and/or MSI via NGS. Clinical variables were correlated with MMR status using nonparametric tests. Among 17,617 patients with solid tumors, 1.4% (n = 242) had LS. A total of 36% (86 of 242) of patients with LS had at least one CRC that underwent NGS profiling, amounting to 99 pooled CRCs assessed. A total of 10% (10 of 99) of CRCs were MMR-P, with 100% concordance between MSS status and retained MMR protein staining. A total of 89% (8 of 9) of patients in the MMR-P group had MSH6 or PMS2 variants, compared with 30% (23 of 77) in the MMR-D group (P = .001). A total of 46% (6 of 13) of PMS2+ patients had MMR-P CRC. The median age of onset was 58 and 43 years for MMR-P and MMR-D CRC, respectively (P = .07). Despite the later median age of onset, 40% (4 of 10) of MMR-P CRCs were diagnosed <50. A total of 60% (6 of 10) of MMR-P CRCs were metastatic compared with 13% (12 of 89) of MMR-D CRCs (P = .002). A total of 33% (3 of 9) of patients with MMR-P CRC did not meet LS testing criteria. Patients with LS remained at risk for MMR-P CRC, which was more prevalent among patients with MSH6 and PMS2 variants. MMR-P CRC was later onset and more commonly metastatic compared with MMR-D CRC. Confirmation of tumor MMR/MSI status is critical for patient management and familial risk estimation.

Perioperative Chemotherapy Could Not Improve the Prognosis of Gastric Cancer Patients With Mismatch Repair Deficiency: A Multicenter, Real-World Study.

To date, the role of deficient mismatch repair (dMMR) remains to be proven in gastric cancer, and it is difficult to judge its value in clinical application. Our study aimed to investigate how MMR status affected the prognosis in patients with gastrectomy, as well as the efficacy of neoadjuvant chemotherapy and adjuvant chemotherapy in patients with dMMR with gastric cancer. Patients with gastric cancer with certain pathologic diagnosis of dMMR or proficient MMR (pMMR) using immunohistochemistry from 4 high-volume hospitals in China were included. Propensity score matching was used to match patients with dMMR or pMMR in 1:2 ratios. Overall survival (OS) and progression-free survival (PFS) curves were plotted using the Kaplan-Meier method and compared statistically using the log-rank test. Univariate and multivariate Cox proportional hazards models based on hazard ratios (HRs) and 95% confidence intervals (CIs) were used to determine the risk factors for survival. In total, data from 6176 patients with gastric cancer were ultimately analyzed, and loss of expression of one or more MMR proteins was observed in 293 patients (293/6176, 4.74%). Compared to patients with pMMR, patients with dMMR are more likely to be older (≥66, 45.70% vs. 27.94%, P < .001), distal location (83.51% vs. 64.19%, P < .001), intestinal type (42.21% vs. 34.46%, P < .001), and in the earlier pTNM stage (pTNM I, 32.79% vs. 29.09%, P = .009). Patients with gastric cancer with dMMR showed better OS than those with pMMR before PSM (P = .002); however, this survival advantage was not observed for patients with dMMR after PSM (P = .467). As for perioperative chemotherapy, results of multivariable Cox regression analysis showed that perioperative chemotherapy was not an independent prognostic factor for PFS and OS in patients with dMMR with gastric cancer (HR = 0.558, 95% CI, 0.270-1.152, P = .186 and HR = 0.912, 95% CI, 0.464-1.793, P = .822, respectively). In conclusion, perioperative chemotherapy could not prolong the OS and PFS of patients with dMMR with gastric cancer.

Abstract 6211: Development and validation of a novel sSTRIDE-MMR functional assay to study the efficiency of MMR inhibitors

Abstract Mismatch repair (MMR) is considered to be one of the fundamental pathways that guards genome stability and mutations in genes encoding for crucial MMR proteins have been shown to promote cancer initiation. On the other hand, inactivation of MMR components in cancer cells leads to increased neoantigen formation and in consequence, exposes the tumor to the immune system. Therapeutic strategies aiming at inhibiting MMR are thus under development, yet methods reporting on the status of MMR are lacking. We report here the development, optimization and validation of a first MMR-specific functional assay. The assay, which is based on the STRIDE platform technology, detects DNA nicks localized in close proximity to PMS2 protein and can thus be utilized as a direct reporter of inhibition of PSM2 itself or upstream acting proteins. The optimization phase of assay development was performed in U2OS cells. First, in untreated cells we have shown that the sSTRIDE-MMR signals constitute ca. 10-15% of total single-strand DNA breaks foci detected by the classic sSTRIDE assay variant. In a series of technical negative controls we have then shown that the number of false-positive foci never exceeds 10% of the total number of signals, with as little as 2% for the isotype controls. The assay was further validated in HAP1 wild-type and PMS2-KO isogenic cell line pair. As expected, the number of sSTRIDE-MMR foci in the PMS2-KO cell line was significantly lower than in wild-type cells and additionally, no response to the treatment with 6TG, a known inducer of MMR, was detected in PMS2 null cells. Finally, the assay was used to verify the efficiency of first-in-class small-molecule MMR inhibitors. After treatment with the compounds, the number of detected sSTRIDE-MMR foci was significantly lower when compared to the number of foci in untreated cells. In conclusion, we show here that sSTRIDE-MMR is an assay characterized by high specificity, low false positives rate and a high-dynamic range. We believe that sSTRIDE-MMR can prove to be a very useful cell-based solution to study the efficiency of MMR inhibitors. Citation Format: Kamil Solarczyk, Karolina Uznańska, Olga Wójcikowska, Maja Białecka, Agnieszka Waligórska, Szymon Koman, Magdalena Kordon-Kiszala. Development and validation of a novel sSTRIDE-MMR functional assay to study the efficiency of MMR inhibitors. [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 6211.

Abstract 4615: Differential immune characteristics and anti-PD-1-induced reinvigoration capacity of tumor-infiltrating lymphocytes according to ProMisE classifier in endometrial cancer

Abstract Endometrial cancer (EC), one of the most common gynecological malignancies, has been gradually increasing worldwide. The Cancer Genome Atlas endometrial collaborative project discovered 4 distinct prognostic genomic subtypes, and the Proactive Molecular Risk Classifier for Endometrial Cancer (ProMisE) was developed: POLE-mutated, mismatch repair deficiency (MMR-D), non-specific molecular profile (NSMP), and p53-abnormal (p53abn). In the era of immunotherapy, immune checkpoint inhibitors (ICIs) become a definite management of EC, both as single agent or in combination with other targeted agents. However, the characteristics of the tumor immune microenvironment according to molecular classification in EC are not well known. This study was conducted to identify distinct immune properties of tumor infiltrating lymphocytes (TILs) according to molecular classification in EC and find optimal therapeutic targets in each molecular subtypes. We isolated peripheral blood mononuclear cells (PBMCs) and TILs from 81 patients with EC. The expression of immune checkpoint receptors and T-cell transcription factors of TILs were examined using flow cytometry. Sixty-six patients were evaluated according to the ProMisE algorithm based on sequencing for the presence of POLE mutations, immunohistochemistry for MMR proteins and p53 (POLE-mut, n=6; MMR-D, n=17; p53abn, n=20; NSMP, n=23). Tumors were categorized into one of the four molecular subtypes. TILs were ex vivo stimulated with anti-CD3 in the presence of anti-PD-1, and their proliferation was assessed to predict ICI-induced reinvigoration capacity of CD8 TILs. Comparing T-cell transcription factors (TCF-1 and TOX), CD8 TILs showed higher expression of TOX, and lower expression of TCF-1. When comparing the immune characteristics of TILs according to molecular subtypes, Tregs of POLE-mut showed significantly lower expression of CTLA-4 and Ki-67 than that of MMR-D. In addition, CD8 TILs of MMR-D showed higher expression of immune checkpoint receptors, including PD-1, CTLA-4, and TIM-3, and lower expression of TCF-1 than those of p53abn. CD8+TILs of p53abn showed significantly higher expression of CD226 than those of MMR-D. In particular, the frequency of antigen reactive CD39+CD103+CD8 T cells significantly lower in p53abn than in MMR-D. CD8 TILs of NSMP showed higher expression of TOX than those of MMR-D. In ex vivo T cell proliferation assay (n=49), 80.0% POLE-mut (4 of 5), 46.2% MMR-D (6 of 13), 35.7% p53abn (5 of 14) and 35.36% NSMP (6 of 17) showed enhanced proliferation of CD8 TILs upon anti-PD-1 treatment. In endometrial cancer, TILs showed distinct immune properties according to ProMisE classification. Further study is needed to develop optimal treatment targets for the p53abn and NSMP subtype, which is non-immunogenic and hardly reinvigorated by ICIs. Citation Format: Jung Chul Kim, Junsik Park, Yong Jae Lee, Sunghoon Kim, Sang Wun Kim, Jung-Yun Lee. Differential immune characteristics and anti-PD-1-induced reinvigoration capacity of tumor-infiltrating lymphocytes according to ProMisE classifier in endometrial cancer. [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 4615.

DNA Mismatch Repair System Imbalances in Breast Adenocarcinoma.

DNA mismatch repair system (MMR) is considered a leading genetic mechanism in stabilizing DNA structure and maintaining its function. DNA MMR is a highly conserved system in bacteria, prokaryotic, and eukaryotic cells, and provides the highest protection to DNA by repairing micro-structural alterations. DNA MMR proteins are involved in the detection and repair of intra-nucleotide base-to-base errors inside the complementary DNA strand recognizing the recently synthesized strand from the parental template. During DNA replication, a spectrum of errors including base insertion, deletion, and miss-incorporation negatively affect the molecule's structure and its functional stability. A broad spectrum of genomic alterations such as promoter hyper methylation, mutation, and loss of heterozygosity (LOH) in MMR genes including predominantly hMLH1, hMSH2, hMSH3, hMSH6, hPMS1, and hPMS2 lead to their loss of base-to-base error repairing procedure. Microsatellite instability (MSI) refers to the DNA MMR gene alterations that are observed in a variety of malignancies of different histological origins. In the current review, we present the role of DNA MMR deficiency in breast adenocarcinoma, a leading cancer-based cause of death in females worldwide.

A comparison of performance of 6-mononucleotide site panel and NCI panel for microsatellite instability detection in patients with colorectal adenocarcinoma

BackgroundMicrosatellite instability (MSI) represents as a molecular hallmark of deficient MMR system at the genomic level. Increasing clinical significance of MSI status highlights the necessity of simple, accurate markers for detection. Although 2B3D NCI panel is the most widely applied, it has been questioned whether the performance of NCI panel is second to none in MSI detection. MethodsWe evaluated the efficacy of the NCI panel versus a 6-mononucleotide site panel (BAT25, BAT26, NR21, NR24, NR27, and MONO-27) in assessing MSI status of 468 Chinese patients with CRC, and compared MSI test results with the results by immunohistochemistry of four MMR proteins (MLH1, PMS2, MSH2, MSH6) in the present study. Clinicopathological variables were also collected, and their associations with MSI or MMR proteins status were analyzed using either the chi-square test or the Fisher’s exact test. ResultsMSI-H/dMMR was significantly associated with right colon involvement, poor differentiation, early stage, mucinous adenocarcinoma, negative lymph node, less neural invasion, and KRAS/NRAS/BRAF wild-type. As to the efficiency of detecting deficient MMR system, both panels had good concordance with MMR proteins expression by IHC, and 6-mononucleotide site panel outperformed NCI panel in sensitivity, specificity, positive predictive value, and negative predictive value numerically despite the lack of statistical significance. The advantage was more obvious in the sensitivity and specificity analyses of each single microsatellite markers from 6-mononucleotide site panel in comparison with NCI panel. Additionally, the rate of MSI-L detected by 6-mononucleotide site panel was much lower than that detected by the NCI panel (0.64% vs. 2.86%, P = 0.0326). Conclusion6-mononucleotide site panel had a greater ability to help resolve cases of MSI-L into either MSI-H or MSS. We propose that 6-mononucleotide site panel may be potentially more suitable than NCI panel for Chinese CRC population. Large-scale studies are warranted to validate our findings.

CD169+ sinus macrophages in regional lymph nodes do not predict mismatch-repair status of patients with colorectal cancer.

Mismatch-repair deficiency and microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC) is treated with programmed death (PD)-1 antibody regardless of PD-ligand (L)1 expression in tumor cells. We previously found that abundant CD169+ macrophages in regional lymph node (RLN) sinuses and CD8+ tumor-infiltrating lymphocytes (TILs) positively correlated in CRC and were associated with a favorable prognosis. However, associations between dMMR/MSI-H CRC and CD8+ TILs or prognoses vary among studies. In this study, we attempted to compare the association between MMR status, CD169+ macrophages in RLNs, CD8+ TILs, PD-L1 scores, and prognoses in CRC. We immunostained 83 surgically resected CRC tumors that we previously analyzed for MMR proteins, and identified 9 that were dMMR. The number of CD169+ macrophages in RLNs and CD8+ TILs significantly correlated with overall survival, whereas MMR status did not. The number of cells positive for the TIL markers CD3, CD4, CD8, and TIA-1, and macrophage markers CD68 and CD169 in RLNs did not significantly differ between groups according to MMR status. Furthermore, combined positive scores (CPS) for PD-L1 expression in five of nine dMMR CRCs were all <1. We found that dMMR in CRC did not correlate with numbers of CD169+ macrophages in RLNs or CD8+ TILs. CRC with CD169+ macrophages in RLNs and abundant CD8+ TILs indicates a better prognosis and it should be immunologically classified as a different antitumor group from dMMR CRC.

Efficacy of adjuvant fluoropyrimidine with or without oxaliplatin therapy in older adults with mismatch repair deficient stage III colorectal cancer.

112 Background: Standard adjuvant chemotherapy regimens for Stage III colorectal cancer (CRC) include FOLFOX/CAPOX, 5-FU/capecitabine, or observation alone. There is uncertainty around the therapeutic benefit of adding oxaliplatin to fluorouracil in older adults over the age of 70 with Stage III CRC, including in those with mismatch repair–deficient (MMR-D) CRC. In this single institutional study, we evaluate progression free survival (PFS) across a 12-year period in patients who receive FOLFOX/CAPOX or 5-FU/capecitabine compared to active surveillance in older adults with MMR-D Stage III CRC. Methods: We identified patients diagnosed with MMR-D Stage III CRC after the age of 70 who received care at our institution and affiliates between 2005-2019. We performed a retrospective chart review of patient outcomes during the 12-year follow up period based on chemotherapy regimen to determine PFS. Patients without MMR-D staining performed at initial time of diagnosis had MMR protein immunohistochemistry performed currently and included in the analysis. Results: Among patients with MMR-D stage III CRC, 50%, 62.5%, and 76% of patients were alive at the end of year 12 with no disease progression in the observation, 5-FU/capecitabine, and FOLFOX/CAPOX groups. The PFS probabilities at one year are 69.6%, 87.5%, and 87.0%, and at five years are 41.8%, 62.5%, and 87.0% in these groups, respectively. Finally, there was a statistically significant difference (P=0.039) in PFS across all chemotherapy regimens in the MMR-D cohort. Conclusions: Based on this study, older adult patients with stage III MMR-D colorectal cancer have an improved progression free survival when treated with oxaliplatin containing chemotherapy compared to active surveillance alone. [Table: see text]

Efficacy and safety of neoadjuvant preoperative short-course radiation followed by envafolimab plus CAPEOX in microsatellite stable (MSS)/mismatch repair proficient (pMMR) locally advanced rectal cancer.

134 Background: Chemoradiation is the standard neoadjuvant treatment for locally advanced rectal cancer. Microsatellite stable (MSS)/ mismatch repair proficient (pMMR) rectal cancer rarely responds to immune checkpoint inhibitor monotherapy, but combination with chemoradiation may improve sensitivity of MSS/pMMR tumors by inducing immune-stimulatory effects. Therefore, we aimed to investigate the efficacy and safety of patients treated with neoadjuvant preoperative short-course radiation followed by envafolimab plus CAPEOX for MSS/pMMR locally advanced rectal cancer. Methods: This is an open-label, single-center, phase ¢ò study. Patients (pts) with locally advanced rectal adenocarcinoma with MSS/pMMR were eligible. MMR protein expression was tested by immunohistochemistry (IHC) £¬and MSI status was confirmed by NGS (next generation sequencing). All pts included in this study underwent neoadjuvant short-course radiation (total dose of 5¡Á5Gy) in the first week after enrollment, then followed by 6 cycles of envafolimab (anti-PD-L1 inhibitor,150mg, d1, subcutaneous injection, QW) plus 2 cycles of CAPEOX in the next six weeks, and subsequently underwent total mesorectal excision (TME) in the ninth week. The primary endpoint is pathological complete response rate. Secondary endpoints include tumor regression grade (TRG), 3 year disease free survival, overall survival, toxicity, and quality of life (QoL). Results: This study intends to recruit 32 pts, and a total of 21 pts were enrolled from January 2022 to September 2022. Overall median age was 67 (42-79) years. 12 pts completed study designed treatment protocol (envafolimab plus CAPOX) followed with TME procedures, and 9 pts are still undergoing neoadjuvant treatment. All 12 pts achieved major partial response (MPR) evaluated by diffusion-weighted magnetic resonance imaging (DW-MRI), and 8 pts (8/12,76.6%) achieved pCR. During neoadjuvant treatment period, 20 pts (20/21, 95.2%) presented with treatment-related AEs (TRAEs) of any grade, 18 pts (18/21, 85.7%) had grade 1-2 and one each pts had grade 3 and 4 thrombocytopenia (2/21, 9.5%). The most common TRAEs were sensation of rectal tenesmus. Conclusions: Neoadjuvant preoperative short-course radiation followed by envafolimab plus CAPEOX in MSS/pMMR locally advanced rectal cancer achieved a promising pathologic response. Meanwhile, this combination neoadjuvant therapy is safe and worthy of application to clinical practice. (Funded by Sir Run Run Shaw Hospital Zhejiang University School of Medicine.) Clinical trial information: NCT05216653 .

Estrogen/Progesterone Receptor Loss, CTNNB1 and KRAS Mutations Are Associated With Local Recurrence or Distant Metastasis in Low-Grade Endometrial Endometrioid Carcinoma.

A subset of endometrial endometrioid carcinomas (EECs) with low-grade histology recur with poor outcomes. Published evidence suggests that poor outcomes may be associated with loss of expression of ER-alpha (ER-α) as well as with β-Catenin-1 ( CTNNB1 ) and Kirsten rat sarcoma viral oncogene homolog ( KRAS ) mutations. This study reports on institutional experience with the incidence of recurrence in low-grade EEC and their association with CTNNB1 and KRAS mutations as well as estrogen/progesterone receptor (ER/PR) expression. Forty-eight (8.5%) out of 568 cases of low-grade EEC with biopsy-proven recurrence were identified; and were analyzed by immunohistochemistry for ER, PR, p53, MMR protein, and mutation analysis for exon 3 of the CTNNB1 and exon 2 of KRAS in relation to recurrence type, local or distant metastasis/recurrence. Twenty-three patients (4%) developed local, and 25 patients (4.4%) developed distant metastases/recurrence. Decreased expression or loss of ER/PR was found in 17/44 (38.6%) patients with recurrence. Eighty-four percent of patients with low-grade EEC and local recurrence had CTNNB1 mutations. Seventy-three percent of patients with distant metastasis/recurrence had KRAS mutations. The association of these mutations with the type of recurrence was statistically significant for both. Five cases with the morphology of low-grade EEC were reclassified as mesonephric-like carcinoma and were universally characterized by distant metastasis/recurrence, loss of ER/PR expression, large tumor size, absence of CTNNB1 mutations, and the presence of KRAS mutations. In low-grade EEC, CTNNB1 and KRAS mutations are associated with local recurrence and distant metastasis/recurrence, respectively, suggesting that these 2 different progression types may be conditioned by tumor genotype. ER/PR immunohistochemistry may be helpful in identifying poor performers in low-grade EEC. Furthermore, identification of the decreased expression or loss of ER/PR in tumors with low-grade histology should prompt consideration of mesonephric-like carcinoma, which is a more aggressive tumor than the low-grade EEC. KRAS mutations were associated with distant metastasis/recurrence in tumors with and without mesonephric-like phenotype.

Status ofPD-1 and PD-L1 expression in invasive urothelial carcinoma ofthebladder with mismatch repair protein deficiency.

It has been reported that mismatch repair deficient (d-MMR) tumors show sensitivity to immune checkpoint inhibitors. We aimed to evaluate thecorrelation ofd-MMR and PD-1/PD-L1 expression in invasive urothelial carcinoma ofthebladder. Tissue microarray (TMA) tissues were stained PD-1/PD-L1 and MMR proteins. Theexpression ratio ofthese markers has been compared with histopathologic parameters. d-MMR tumors were more superficial muscle invasive (p=0.012). When thed-MMR, and PD-1/PD-L1 expression ratios were examined, asignificant correlation was obtained between thed-MMR and PD-L1 expression ratio of> 5% in both thetumor and immune cells (p=0.02 and p=0.004, respectively). Theexpression ratio was higher in thepatients without MMR loss. PD-1 and PD-L1expression in those with MSH6 loss was one or none. When PD1/PDL1 expression was compared with histopathological parameters, asignificant relationship was observed between tumor grade and depth ofmuscle invasion. PD-L1 expression was not observed in thesuperficial muscle invasive tumors. This study was shown thestatus ofd-MMR and PD-1/PD-L1 in invasive urothelial cancers and their correlation with prognostic markers. PD-1/PD-L1 expression may contribute to theprogression and poor prognosis ofbladder cancer. However, further studies are required to research theclinical utility.

The statuses of HER2 expression and mismatch repair in endometrial clear cell carcinoma.

High-grade endometrial carcinomas (HGEC) are difficult to classify. With the current use of HER2-based therapy in serous carcinoma, a diagnosis of clear cell carcinoma (CCC) has the potential to exclude patients from receiving therapy. Therefore, we examined HER2 expression in our CCC patients. The preparations of 8 patients with CCC who underwent hysterectomy, bilateral salpingo-oophorectomy, and lymph node dissection were re-evaluated. Patients did not have any prior treatment. Histopathologic parameters that were evaluated include cytoplasmic clearing, nuclear atypia, mitotic activity, hobnail architecture, hyalinized cores, hyaline globules, stratification of epithelial lining papillae, or glandular structures, and highly atypical cell layers. Immunohistochemically, HER2, ER, PR, HNF1β, Napsin A, MLH1, MSH2, MSH6 and PMS2 were applied. HER2 staining pattern, ASCO/CAP protocol used for endometrial carcinom was used. HER2 was positive in 3 of our 8 CCC patients (37.5%). While all of our HER2+cases were Napsin A and HNF1β positive, MMR proteins were intact and ER and PR were negative. Two patients had wild type p53 and 1 patient had aberrant p53 staining. Considering that there is not always a consensus between SC and CCC, even among gynecopathologists, tumor heterogeneity and different tumor components may exist, and while patients may be diagnosed with CCC and benefit from HER2 therapy, there is also a possibility that they may not benefit from the treatment. The fact that 37.5% of our CCC cases were HER2+is a finding with strong implications for the therapeutic approach. As a result of our study, in patients with CCC, if MMR is intact and ER-PR is negative, regardless of the p53 staining pattern, HER2 testing may be an objective screening method for patients who are likely to benefit from HER-targeted therapy. Consequently, patients with a diagnosis of CCC can be candidates for future clinical trials of HER2-targeted therapy.