Role Of Microsatellite Instability Research Articles

Clinicopathological significance of microsatellite instability and immune escape mechanism in patients with gastric solid-type poorly differentiated adenocarcinoma.

In gastric solid-type poorly differentiated adenocarcinoma (PDA), the role of microsatellite instability and immune escape mechanism remains unclear. The current study aimed to elucidate the clinical significance of mismatch repair (MMR) status, genome profile, C-X-C motif chemokine receptor 2 (CXCR2) expression, and myeloid-derived suppressor cell (MDSC) infiltration in solid-type PDA. In total, 102 primary solid-type PDA cases were retrieved, and classified into 46 deficient-MMR (dMMR) and 56 proficient-MMR (pMMR) cases based on immunohistochemistry (IHC) and polymerase chain reaction-based molecular testing results. The mRNA expression profiles (NanoString nCounter Assay) of stage-matched dMMR (n = 6) and pMMR (n = 6) cases were examined. The CXCR2 expression and MDSC infiltration (CD11b- and CD33-positive cells) were investigated via IHC in all solid-type PDA cases. mRNA analysis revealed several differentially expressed genes and differences in biological behavior between the dMMR (n = 46) and pMMR (n = 56) groups. In the multivariate analysis, the dMMR status was significantly associated with a longer disease-free survival (hazard ratio = 5.152, p = 0.002) and overall survival (OS) (hazard ratio = 5.050, p = 0.005). CXCR2-high expression was significantly correlated with a shorter OS in the dMMR group (p = 0.018). A high infiltration of CD11b- and CD33-positive cells was significantly correlated with a shorter OS in the pMMR group (p = 0.022, 0.016, respectively). dMMR status can be a useful prognostic predictor, and CXCR2 and MDSCs can be novel therapeutic targets in patients with solid-type PDA.

Role of Microsatellite Instability as Pan-Cancer Agnostic Marker of Solid Tumours in Personalized Medicine

Role of Microsatellite Instability as Pan-Cancer Agnostic Marker of Solid Tumours in Personalized Medicine

Unusual pattern of microsatellite instability in gastric neuroendocrine tumor

Abstract Introduction/Objective Evaluation of microsatellite instability (MSI) is routinely performed in gastrointestinal tract adenocarcinomas including gastric adenocarcinoma. It confers a good prognosis and is predictive of response to immunotherapy. However, the role of MSI in prognosis and treatment of well differentiated neuroendocrine tumors is controversial. Accordingly, MSI status is not extensively evaluated in neuroendocrine tumors. Limited available literature reports the usual paired losses and loss of MSH6 only in gastric well differentiated neuroendocrine tumor is unheard of. The purpose of this case is to report loss of MSH6 only in a patient with gastric well differentiated neuroendocrine tumor, grade 2. Methods/Case Report A 64-year-old female presented with abdominal pain and nausea. Endoscopy revealed erythematous nodules in the stomach which were removed by endoscopic mucosal resection. Microscopically, the tumor had vague nested appearance with areas more infiltrative appearance. However, cytologically tumor cells were bland and monotonous. Immunohistochemical stains showed the tumor cells to be positive for synaptophysin, chromogranin, pancytokeratin, and Cam 5.2, and negative for CK 7, CK 20 and CDX2. Ki-67 proliferation index was 3.7%. Therefore, diagnosis of well differentiated neuroendocrine tumor, grade 2 was rendered. Additionally, MSI by immunohistochemistry was ordered which showed intact nuclear expression of MSH2, MLH1 and PMS2 but loss of nuclear expression for MSH6. Results (if a Case Study enter NA) NA Conclusion This case highlights the fact that MSI in gastric neuroendocrine tumors can manifest as only MSH6 loss. Whether or not, it is of clinical and prognostic utility, is still up for debate.

The results of treatment for resectable gastric cancer with microsatellite instability

Background. microsatellite instability (MSI) is a prognostic marker of survival in many malignant diseases and show resistance to chemotherapy at early stages of colorectal cancer and show no benefits from chemotherapy at early stages of colorectal cancer. However, the role of MSI in resectable gastric cancer (GC) remains unknown.Aim. To study the results of treatment of resectable gastric cancer with microsatellite instability.Materials and methods. The study included 286 patients with resectable gC who received treatment at the N. N. Blokhin national medical Research Center of Oncology. All patients underwent PCR testing for MSI-H in 5 markers (BAT25, BAT26, NR21, NR24, NR27). Tumor regression grades (TRG) were evaluated according to the mandard tumour regression score, including disease-free survival and overall survival.Results. MSI indicated in 27 cases (9.44 %) out of 286 resectable gastric cancer. In group patients who received only surgical treatment, 2-year disease-free survival in patients with MSI-H was 77.80 % versus 88.29 % in MSS patients (hazard ratio (HR) 1.82, 95 % confidence interval (CI) 0.37–8.82, p = 0.45), 2-year overall survival in patients with MSI-H was 88.90 % versus 95.36 % in MSS patients (HR 2.03, 95 % CI 0.20–19.8, p = 0.54). In patients who received perioperative chemotherapy, 28.57 % (4 / 14) had progression in MSI-H tumor versus 3.61 % (6 / 166) in MSS tumor (p <0.001). In group patients who received treatment combined with chemotherapy, 2-year disease-free survival in patients with MSI-H was 59.60 % versus 67.36 % (HR 1.96, CI 95 % 0.88–4.35, p = 0.09), 2-year overall survival in patients with MSI-H was 67.30 % versus 85.86 % in MSS patients (HR 1.86, 95 % CI 0.64–5.41, p = 0.25)Conclusion. MSI-H is not a favorable prognosis factor in patients with resectable GC who are treated surgically combined with chemotherapy. The prevalence of progression in patients with MSI-H-status is higher than MSS-status with perioperative chemotherapy (FLOT / FOLFIRINOX).

Role of microsatellite instability and HER2 positivity in locally advanced esophago-gastric cancer patients treated with peri-operative chemotherapy.

Neoadjuvant chemotherapy (NAC) significantly improved the prognosis of patients with locally advanced gastric cancer (LAGC). Several biomarkers, including HER2 and MMR/MSI are crucial for treatment decisions in the advanced stage but, currently, no biomarkers can guide the choice of NAC in clinical practice. Our aim was to evaluate the role of MSI and HER2 status on clinical outcomes. We retrospectively collected LAGC patients treated with NAC and surgery +/- adjuvant chemotherapy from 2006 to 2018. HER2 and MSI were assessed on endoscopic and surgical samples. Pathologic complete response (pCR) rate, overall survival (OS), and event-free survival (EFS) were estimated and evaluated for association with downstaging and MSI. We included 76 patients, 8% were classified as MSI-H, entirely consistent between endoscopic and surgical samples. Six percent of patients were HER2 positive on endoscopic and 4% on surgical samples. Tumor downstaging was observed in 52.5% of cases, with three pCR (5.1%), none in MSI-H cancers. According to MSI status, event-free survival (EFS) and overall survival (OS) were higher for MSI-H patients to MSS [EFS not reached vs 30.0 months, p=0.08; OS not reached vs 39.6 months, p=0.10]. Our work confirms the positive prognostic effect of MSI-H in the curative setting of LAGC, not correlated with pathologic tumor downstaging. Prospective ad-hoc trial and tumor molecular profiling are eagerly needed.

High Frequency of Microsatellite Instability among Non-Metastatic Gastric Cancer.

Background: Microsatellite instability (MSI) is considered a key factor in carcinogenesis and a genetic alteration pattern in many types of cancers such as gastric cancer (GC). Although the role of MSI in colorectal cancer (CRC) is well known, its prognostic impact on GC has not been clearly defined. The assessment of MSI in GC has notbeen documented in the Iranian population yet. Therefore, this study analyzed the association of MSI status with GC in Iranian patients. Materials and Methods: We compared the frequency of MSI at 5 loci from formalin-fixed paraffin-embedded (FFPE) gastrectomy specimens, between metastatic and non-metastatic cases of GC (N = 60). A panel of five quasi-monomorphic markers and a single dinucleotide marker with linker-based fluorescent primers was used. Results: MSI was observed in 46.6% of cases, including MSI-high (H) (33.3%) and MSI-Low (L) (13.3%). Moreover, the most unstable and stable markers in our study were NR-21 and BAT-26 accordingly. MSI-H and MSI were seen more frequently in non-metastatic tumors (p= 0.028 and p= 0.019, respectively). Conclusion: The current study showed MSI status more frequently in non-metastatic GC which may reflect a good prognostic factor in GC like CRC. Although, larger and more comprehensive studies are needed to confirm this statement. A panel consisting of NR-21, BAT-25, and NR-27 mononucleotide markers appears to be reliable and useful markers for detecting MSI in GC in Iranian patients.

ABCC9 Is Downregulated and Prone to Microsatellite Instability on ABCC9tetra in Canine Breast Cancer.

Tumorigenesis is associated with metabolic abnormalities and genomic instability. Microsatellite mutations, including microsatellite instability (MSI) and loss of heterozygosity (LOH), are associated with the functional impairment of some tumor-related genes. To investigate the role of MSI and LOH in sporadic breast tumors in canines, 22 tumors DNA samples and their adjacent normal tissues were evaluated using polyacrylamide gel electrophoresis and silver staining for 58 microsatellites. Quantitative real-time polymerase chain reaction, promoter methylation analysis and immunohistochemical staining were used to quantify gene expression. The results revealed that a total of 14 tumors (6 benign tumors and 8 breast cancers) exhibited instability as MSI-Low tumors. Most of the microsatellite loci possessed a single occurrence of mutations. The maximum number of MSI mutations on loci was observed in tumors with a lower degree of differentiation. Among the unstable markers, FH2060 (4/22), ABCC9tetra (4/22) and SCN11A (6/22) were high-frequency mutation sites, whereas FH2060 was a high-frequency LOH site (4/22). The ABCC9tetra locus was mutated only in cancerous tissue, although it was excluded by transcription. The corresponding genes and proteins were significantly downregulated in malignant tissues, particularly in tumors with MSI. Furthermore, the promoter methylation results of the adenosine triphosphate binding cassette subfamily C member 9 (ABCC9) showed that there was a high level of methylation in breast tissues, but only one case showed a significant elevation compared with the control. In conclusion, MSI-Low or MSI-Stable is characteristic of most sporadic mammary tumors. Genes associated with tumorigenesis are more likely to develop MSI. ABCC9 protein and transcription abnormalities may be associated with ABCC9tetra instability.

Interaction between Microsatellite Instability (MSI) and Tumor DNA Methylation in the Pathogenesis of Colorectal Carcinoma.

Simple SummaryIn colorectal cancer (CRC), mutations may occur in short, repeated DNA sequences, known as microsatellite instability (MSI). Tumor DNA methylation is another molecular change now recognized as an important biomarker in CRC. In a genome-wide scale, for the first time, we explored whether DNA methylation is associated with MSI status in CRC. We analyzed 250 paired samples (tumor and corresponding normal) from 125 CRC patients (m = 72, f = 53) at different stages. We found that many genes were methylated in tumor tissue compared to normal tissue. However, almost four times more genes showed such methylation changes in the tumor if the patient who also had MSI compared to patients without MSI. Our study shows an association of MSI and DNA methylation in CRC. The study also indicates an opportunity for potential use of certain immune checkpoint inhibitors (CTLA4 and HAVCR2 inhibitors) in CRC with MSI.In colorectal cancer (CRC), the role of microsatellite instability (MSI) is well known. In a genome-wide scale, for the first time, we explored whether differential methylation is associated with MSI. We analyzed 250 paired samples from 125 CRC patients (m = 72, f = 53) at different stages. Of them, 101 had left-sided CRC, 30 had MSI, 34 had somatic mutation in KRAS proto-oncogene (KRAS), and 6 had B-Raf proto-oncogene (BRAF) exon 15p.V600E mutation. MSI was more frequent in right-sided tumors (54% vs. 17%, p = 0.003). Among the microsatellite stable (MSS) CRC, a paired comparison revealed 1641 differentially methylated loci (DML) covering 686 genes at FDR 0.001 with delta beta ≥ 20%. Similar analysis in MSI revealed 6209 DML covering 2316 genes. ANOVA model including interaction (Tumor*MSI) revealed 23,322 loci, where the delta beta was different among MSI and MSS patients. Our study shows an association between MSI and tumor DNA methylation in the pathogenesis of CRC. Given the interaction seen in this study, it may be worth considering the MSI status while looking for methylation markers in CRC. The study also indicates an opportunity for potential use of certain immune checkpoint inhibitors (CTLA4 and HAVCR2 inhibitors) in CRC with MSI.

Microsatellite instability (MSI, EMAST) in the pathogenesis of follicular lymphoma

Background. Genetic instability, an important phenomenon involved in oncogenic transformation and tumor progression, is associated with the insufficiency of the multicomponent DNA repair complex, in particular, the nucleotide mismatch repair (MMR) system. The MMR defect manifests itself as abnormalities in DNA microsatellite repeats, or microsatellite instability (MSI). In the studies of colorectal cancer, the role of MSI in prognostication of the disease, and defining the choice of specific therapy with immune checkpoint inhibitors has been proven.However, in lymphatic system tumors, the significance of this phenomenon is poorly understood. Determination of genetic instability in the onset of follicular lymphoma, a disease characterized by a heterogeneous course, may have prognostic value.Objective: to determine the genetic instability at the onset of follicular lymphoma.Materials and methods. Here we report an analysis of 24 microsatellite repeats and amelogenin loci in tumor cells of 46 follicular lymphoma patients.Results. In the studied cohort, lesions in microsatellite repeats were presented by MSI in 9 cases (19.6 %) and the loss of heterozygosity (LOH) in 19 cases (41.3 %). Most frequent lesions were found for the SE33 marker located at the q14 locus of chromosome 6. A significant association was shown between MSI and the double-hit follicular lymphoma group with rearrangements of the MYC and BCL2/BCL6 genes.Conclusion. Thus, our data indicate that the MSI phenomenon might be involved in the pathogenesis of the lymphatic tumors and particularly follicular lymphoma. However further studies on the expanded cohorts of patients are required to define the possible prognostic value of MSI in lymphatic tumors.

Prognostic impact of microsatellite instability in gastric cancer.

Gastric cancer is a common and deadly cancer. Several factors are associated with its prognosis; however, controversy exists about the role of microsatellite instability (MSI). We aimed to determine the 5-year overall survival (OS) of MSI in gastric adenocarcinoma.A cross-sectional study was carried out on gastric adenocarcinoma in clinical stages I to III treated with D2 gastrectomy between 2010–2013. MSI was demonstrated by immunohistochemistry. We performed a survival analysis comparing cases with and without MSI.From 102 cases, 9.8% showed MSI. The median age was 63 years (range 33–91 years), and 57.8% were men. The more prevalent site of occurrence was the antrum (46.1%), 78.5% of the cases presented in stage III, 47.1% were of the diffuse type, 45.1% were of an intestinal type, and 7.8% were mixed. MSI cases were associated with lower clinical stages (stages I–II) and with better 5-year OS (100 vs. 47 months, p = 0.017). In a multivariate analysis, MSI was independently associated with better survival (HR = 0.209, 95% CI: 0.046–0.945, p = 0.042). MSI gastric cancers presented in early clinical stages and had favourable prognosis compared with non-MSI cancers.

Immune-Based Therapies and the Role of Microsatellite Instability in Pancreatic Cancer.

Pancreatic cancer is one of the most aggressive malignancies with limited treatment options thus resulting in high morbidity and mortality. Among all cancers, with a five-year survival rates of only 2–9%, pancreatic cancer holds the worst prognostic outcome for patients. To improve the overall survival, an earlier diagnosis and stratification of cancer patients for personalized treatment options are urgent needs. A minority of pancreatic cancers belong to the spectrum of Lynch syndrome-associated cancers and are characterized by microsatellite instability (MSI). MSI is a consequence of defective mismatch repair protein functions and it has been well characterized in other gastrointestinal tumors such as colorectal and gastric cancer. In the latter, high levels of MSI are linked to a better prognosis and to an increased benefit to immune-based therapies. Therefore, the same therapies could offer an opportunity of treatment for pancreatic cancer patients with MSI. In this review, we summarize the current knowledge about immune-based therapies and MSI in pancreatic cancer.

Current status on microsatellite instability, prognosis and adjuvant therapy in colon cancer: A nationwide survey of medical oncologists, colorectal surgeons and gastrointestinal pathologists.

BackgroundThere is significant variation in attitude both towards the role of microsatellite instability (MSI) in predicting prognosis, and towards its role in guiding which Stage II colon cancer patients may benefit from adjuvant chemotherapy.AimTo examine the current status of specialist attitudes towards MSI in guiding prognosis and adjuvant therapy in stage II colon cancer.MethodsThe Pathology in Colon Cancer, Prognosis and Uptake of Adjuvant Therapy (PiCC UP) Australia and New Zealand questionnaire was distributed to colorectal surgeons, medical oncologists and pathologists after institutional board approval. A 5‐scale Likert score was used to assess attitudes towards 23 pathological features for prognosis and 18 features for adjuvant therapy. Data were analysed using a rating scale and graded response model in item response theory (IRT) on STATA (Stata MP, version 15; StataCorp LP).Results164 specialists (45 oncologists, 86 surgeons and 33 pathologists) participated. 80.5% regularly attended colorectal multidisciplinary team (MDT) meetings. 89.63% and 59.26% of specialists reported that MSI status was likely or definitely to influence prognosis in colon cancer and recommendations for adjuvant therapy in Stage II colon cancer respectively.IRT modelling was achieved in 17 pathological features for prognosis. MSI IRT score was 4.47 (95% CI: 4.05‐4.68). IRT modelling was achieved in 10 pathological features for adjuvant therapy. MSI IRT score was 3.62 (2.89‐4.15). MSI ranked 10 (of 17) in order of importance in determining prognosis and ranked three (of 10) in guiding adjuvant therapy.ConclusionMSI status is considered an important biomarker when selecting patients for adjuvant therapy in Stage II colon cancer. MSI is also considered useful in prognostication of colon cancer. MSI status was ranked similar to the tumour grade of differentiation and the presence of perineural invasion.

Abstract 5296: Instability of non standard microsatellites in metastatic colorectal cancer patients treated with a bevacizumab based chemotherapy

Abstract Bevacizumab (B) is a biological agent frequently included in the treatment of metastatic colon cancer (mCRC), although at present there is no effective biomarker that can predict its efficacy. Few studies report a positive association of microsatellite instability (MSI) with the response to anti-angiogenic therapy, but the role of MSI in relation to B efficacy needs to be better understood. Elevated microsatellite alterations at selected tetranucleotides repeats (EMAST) can be observed at higher rate in mCRC patients compared to MSI. The predictive and prognostic role of EMAST has not been completely investigated so far. Moreover, it is known that angiogenesis in mCRC goes through the activation of VEGF-A, but VEGF-B can be involved in some compensatory effect during anti-VEGF-A treatments. By exploring the UCSC Genome Browser database, we found that the VEGF-B gene possesses a poly-dinucleotide microsatellite (normally 19xAG) which somatic instability has never been reported. In this study, we analyzed the status of MSI, five EMAST markers (D20S82, D20S85, D8S321, D9S242, MYCL1) and the VEGF-B microsatellite in relation to prognosis in 145 mCRC patients treated with chemotherapy alone (n=51) or chemotherapy plus B (n=94). MSI high (MSI-H) was detected in four patients (3%) out of 141 participants. Using a multivariable model and adjusting for patient characteristics, microsatellite status remains significantly associated with progression free survival (PFS) and overall survival (OS). The PFS hazard ratio (HR) for MSI-H patients was 3.18 (95% CI 1.09-9.25; p=0.034) and the OS HR was 6.45 (95% CI 2.08-19.99; p=0.001). Eleven (7.8%) patients out of 140 were positive to at least two EMAST markers. EMAST instability was associated with a general worse prognosis, trend that become significant in the group of patients treated with CT plus B in term of PFS (median survival 5 months vs 11. months, p=0.0006) and OS (median survival 6.1 months vs 29.1 months, p<0.0001). The interaction test showed a significant association of D20S82 (PFS p=0.004) and MYCL1(PFS p=0.029), with worse prognosis when treated with CT plus B, adding a possible predictive value in mCRC patients. The 24.2% of patients (29 out of 120) showed a VEGF-B-poly-AG instability. Amplification of the poly-AG is associated with worse outcome in PSF (7.0 month of median survival vs 28.0 months for patients with shortened poly-AG; p=0.005) in patients treated with CT alone, suggesting that an extended microsatellite in VEGF-B might have a role in the resistance to chemotherapy. In conclusion, MSI, EMAST and VEGF-B poly-AG instability are associated with prognosis in mCRC patients treated with CT or CT plus B. MSI and EMAST instability are associated with worse prognosis in CT+B patients, while VEGF-B microsatellite instability is linked to worse prognosis in CT patients. Further investigations are needed but we can hypothesize that MSI, EMAST and VEGF-B poly-AG instability can have some relevance for the clinical outcome of the disease. Citation Format: Francesca Pirini, Luigi Pasini, Sara Ravaioli, Gianluca Tedaldi, Emanuela Scarpi, Giorgia Marisi, Chiara Molinari, Daniele Calistri, Alessandro Passardi, Paola Ulivi. Instability of non standard microsatellites in metastatic colorectal cancer patients treated with a bevacizumab based chemotherapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5296.

Abstract 3537: Evaluation of genomic instability using microsatellite instability, ploidy status, and p53 expression in archival paraffin embedded tissue from primary ovarian cancer specimens

Abstract A retrospective study of a subset of ovarian cancer cases was evaluated to assess the role of microsatellite instability (MSI) and ploidy status. P53 function is important in the regulation of genomic stability and its expression was examined by immuno-histochemical staining. Genomic instability is also considered a possible indicator of immuno-therapy responsive tumors. Ovarian cancer patients diagnosed between 1983 to 1987 at Saskatoon Cancer Center, Canada, were evaluated for genomic stability. Nearly 400 Epithelial Ovarian Cancer (EOC) cases were reviewed, and Paraffin Embedded Tissue (PET) blocks from 112 cases were retrieved from hospitals in the region. PET blocks containing over 70% neoplastic tissue were chosen for the study. P53 expression was determined in eighteen cases using the mouse monoclonal antibody D07. An assessment of MSI and LOH was performed using the PCR mixes from Perkin Elmer (PE) AB. The replication error repair (RER)/Loss of Heterozygosity (LOH) assays were performed at nine loci using the primers obtained from PE. Fourteen out of eighteen cases were evaluated for ploidy status using a method described in literature[1]. Statistical analyses were performed to determine the significance of MSI/LOH, ploidy status, and p53 expression. In this study, 34 (30%) of 112 EOC cases were found to be aneuploid. Fourteen EOC cases had ploidy status that could be evaluated. Of the eighteen patients analyzed for MSI, at least nine patients showed instability at one or more loci. Of these nine, there were two RER positive phenotypes with aneuploid DNA content which were also p53 immuno-negative. Of the seven (78%) RER negative tumors, 57% (4/7) p53 negative, and the remaining three cases overexpressed p53. In five EOC cases, with an RER negative phenotype, 60% (3/5) were aneuploid and 40% (2/5) were diploid. Furthermore, LOH was a common event at the nine loci. The three events: MSI, lack of p53 overexpression, and aneuploidy, may be characteristics of a subset of ovarian cancer cases. Secondly, the study suggests that RER positivity occurs in ovarian cancer pathogenesis. We conclude that the data indicates general genomic instability due to MSI and DNA ploidy status. [1] A. Geissel and J. L. Griffin, “Preparation of nuclei for flow cytometry,” in AFIP Advances in Laboratory Methods in histology and Pathology, ed. Mikel UV (Washington DC: American Registry of Pathology, 1994), 111-121. Citation Format: Kavitha Advikolanu Rao, Anthony M. Magliocco, Andrew W. Maksymiuk. Evaluation of genomic instability using microsatellite instability, ploidy status, and p53 expression in archival paraffin embedded tissue from primary ovarian cancer specimens [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3537.

Computational studies to explore the role of MSI associated DNA mismatch repair mechanisms in HNPCC through expression and interaction data

Microsatellite instability (MSI) is an error mechanism associated with DNA mismatch repair (MMR) system constituting a set of genes. If MMR fails, MSI may lead to various forms of cancers such as hereditary non polyposis colorectal cancer (HNPCC). In this study, we explored the gene expression and network data to reveal the significance of MSI in HNPCC. Genes and proteins were observed for their specific role in HNPCC with respect to MSI and MMR. Besides standard markers, few genes such as PMS1, TP53, MLH1, CHEK2, RFC3, LIG1, AURKA, CCND1, POLD1, HMGB1, ERCC1, ERCC2, PTGS2, and SLC19A1were identified as putative markers having significant contribution in the regulation of the mechanisms associated with MSI and MMR for HNPCC. Experimental validation of these genes will prove to be a promising outcome for further research and will aid in understanding of the disease.

MICROSATELLITE INSTABILITY AND GASTRIC CARCINOMA. REVIEW OF THELITERATURE

Carcinoma of the stomach is wide spread malignancy with the poor prognosis. Recent investigations of the genome features let to consider this tumor as heterogeneous lesion, presenting different biological subtypes. Each of those subtypes has its own definitive characteristics including difference in prognosis. Microsatellite instability (MSI) – epigenetic molecular abnormality known in many tumors. The role of MSI in the carcinoma of stomach, prognostic as well predictive, is still not clear. High incidence (10 up to 22 %) of MSI in carcinoma of stomach requires performing more extensive studying of this malignancy. The present review is dedicated to recent data of the literature, concerning clinical, morphological, prognostic and predictive features of MSI in the carcinoma of stomach.

Abstract 1741: Identification of microsatellite instability in hematologic malignant cell lines

Abstract Defective DNA repair machinery which is a consequence of chromosomal or molecular alterations is associated with variety of diseases including solid tumors. Cytogenetic analysis is an important tool in diagnosis and treatment of hematologic malignancies. Our aim is to understand the role of microsatellite instability in initiation and progression of blood cancers. Here we hypothesize that leukemogenic cells may carry defective repair mechanisms that contribute to other genomic instabilities. In order to explore the possible role of microsatellite instability (MSI) in leukemia and lymphoma, eight different DNA repair genes involved in mismatch repair (MMR) and direct reversal of damage (DRD) were analyzed in K562 (CML), Molt-4 (T-ALL) and Daudi (Burkitt’s lymphoma) cell lines. Fragment analysis was carried out using novel primers considering repeat motifs enriched with (A)n, (CA)n and (AT)n for instability. Almost all the cell lines showed moderate to high level of microsatellite instability and exhibited a shift in selected repeat regions indicating possible loss (66.7%) (MSH2, MSH4, MSH6, MLH1, MLH3, PMS1) or gain (25%) (MSH3, MGMT) of nucleotide repeats as compared to normal DNA. The K562, Philadelphia negative CML cell line appeared to be microsatellite stable (MSS) for genes MSH2 and MLH1. Treatment induced microsatellite instability is known in leukemic patient cells as also seen in Molt-4 cells. Our present and previous observations suggest that MSI is a non-random event in leukemia/lymphoma which needs confirmatory future studies in newly diagnosed untreated patient samples. Considering the fact that both MSI and MSS represents two distinct molecular pathways of carcinogenesis, assessment of MSI, if added as distinct diagnostic criteria, can possibly refine early detection and help in identifying novel targets in management of hematologic malignancies. Citation Format: Priyanjali Bhattacharya, Naveed Anjum Chikan, Arati Sharma, Dhimant Desai, Charyguly Annageldiyev, Pinaki Patel, Trupti N. Patel. Identification of microsatellite instability in hematologic malignant cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1741.

Clinicopathological and prognostic significance of microsatellit instability (MSI) status and PDl-1 expression in Turkish patients with gastric cancer.

e15538 Background: The aim of this study was to evaluate the prognostic role of microsatellite instability (MSI) status and PD-L1 expression in surgically resected gastric cancer and the relationship of these parameters with clinicopathological features. Methods: Eighty six gastric cancer patients which had curative surgical resection at Acibadem Atakent and Maslak Hospitals between 2010 and 2017 were analysed. Tumor samples were evaluated with MSI and PD-L1 antibodies by immunohistochemical (IHC) methods. PD-L1 IHC scoring was performed using the combined positive score (CPS). Survival analysis was accomplished using the Kaplan-Meier method. Cox proportional hazard regression model was used to identify independent risk factors that affect patients' overall survival. Results: The rate of PD-L1 expression in tumor cells was 34.9% (n = 30) and the frequency of PD-L1 expression in immune cells with CPS (≥1%) was 57% (n = 49). MSI-H was detected in 11.6%(n = 10), and more observed in PD-L1 positive cases (p = 0.021). MSI-H status was significantly correlated with older age, increased tumor size, presence of PD-L1 expression, and adenocarcinoma subtype. PD-L1 expression was associated with lymph node metastasis, adenocarcinoma subtype, microsatellite instability, presence of preoperative treatment and improved response to preoperative chemotherapy. In our study, the impact of MSI status on survival was not demonstrated, but PD-L1 expression positivity(≥1%) in both tumor cells (15.7 vs 53.4 months, p = 0.008)and in immune cells (20.4 vs NR; p = 0.027) was associated with short overall survival. PD -L1 expression in tumor cells was an independent prognostic factor for overall survival in multivariate analysis (HR: 2.28, p = 0.047). Conclusions: PD-L1 expression was related to a poor prognosis in patients with gastric cancer and can represent a rational approach for PD-1/PD-L pathway-targeted immunotherapy.

Is there a correlation between clinic-pathological features, MSI, PD-L1 and survival outcomes in resected gastric cancer? Looking for optimal biomarkers.

e15566 Background: Identification of prognostic biomarkers for gastric cancer (GC) patient selection is compelling to improve survival outcomes. Microsatellite instability (MSI) is related with a positive prognostic effect in GC, whereas perioperative chemotherapy resulted detrimental in this subgroup. In metastatic GC, immunotherapy with anti-PD1/PD-L1 drugs has shown promising results. Nevertheless, in early stages, data on the relation between MSI, clinic-pathological features, PD-L1 expression and overall survival (OS) remains sparse, especially in Western population. In our study, the prognostic role of MSI, clinic-pathological features and PD-L1 expression in a cohort of Italian GC patients was examined. Methods: CP data of 148 consecutive stage I-III GC pts resected in Cremona Institute between 2010 and 2014 (mostly chemo and/or radio-naive) were collected. MSI analysis was performed on tissue samples for all cases by polymerase chain reaction. PDL-1 expression, evaluated by immunohistochemistry, was assessed in MSI group. Differences between subgroups were evaluated with Chi-square test; Kaplan-Meier method and Long Rank test were used to calculate OS. Results: Female sex (p=0.012), earlier TNM stages (p=0.011) and limited nodal involvement (p=0.29) significantly correlated with MSI status. MSI is significantly associated with better prognosis, exhibiting an advantage of 28.6 months in OS compared with microsatellite stable subgroup (p<0.001). Most MSI patients expressed PD-L1. MSI patients without PD-L1 expression showed higher percentage of clinical features correlated with better prognosis compared with PD-L1 expressing MSI patients and MSS subgroup. Conclusions: MSI is an independent prognostic biomarker in GC and identifies a subset of patients with better OS and specific clinic-pathological features, including high percentage of PD-L1 expression. MSI could represent a promising biomarker to select patients for chemotherapy versus immunotherapy in non-metastatic disease.

Clinicopathologic Characterization of Bilateral Testicular Germ Cell Tumors With Immunohistochemical Evaluation of Mismatch Repair and BRAF (V600E) Genes Mutations.

The incidence of bilateral testicular germ cell tumor (TGCT) is 1% to 5%. Despite the high rate of treatment success, resistance to chemotherapy has a detrimental effect. Some studies found MMR and BRAF gene mutations to be associated with chemotherapy resistance, which has not been found by others. However, the role of microsatellite instability (MSI) and BRAF mutations in bilateral disease has not been investigated. In this article, we studied the clinicopathologic characteristics and immunohistochemical expressions of MMR and BRAF in 13 patients with bilateral TGCT. Bilateral tumors were found in 4% of patients in our data. The mean ages at the first and subsequent diagnoses were 26.9 and 28.3 years, respectively. Eleven patients had metachronous disease; and the mean period between both tumors was 4.9 years. Six had mixed GCTs (MGCT) initially and later developed contralateral seminoma, 3 had bilateral MGCTs; 1 initially had pure embryonal carcinoma and subsequently MGCT and finally, 1 patient had initial seminoma and contralateral germ cell neoplasia in situ only. Of the patients with synchronous GCT, 1 had a MGCT and contralateral non-seminoma and 1 had seminoma and contralateral MGCT. In metachronous cases, 40% and 78% had an initial and subsequent stage of pT1, respectively. Hormonal and/or metastatic recurrence was observed in 30% of metachronous tumors. Six patients received chemotherapy, including patients with metastasis. No progression occurred after therapy. MLH1, PMS2, MSH2, and MSH6 staining was retained in all tumors. No BRAF staining was found. In conclusion, we found no association between bilateral TGCT and the MMR/MSI pathway and that subsequent metachronous tumors behaved much more indolently.