High-level Microsatellite Instability Research Articles

Esophagogastric junction adenocarcinoma shares characteristics with gastric adenocarcinoma: Literature review and retrospective multicenter cohort study.

The incidence of esophagogastric junction (EGJ) adenocarcinoma has been gradually increasing in Asia, just like in Western countries a few decades ago. Despite recent advances in next‐generation sequencing and multimodal treatments, EGJ adenocarcinoma is still an aggressive malignancy with poor outcomes. Clinically, EGJ adenocarcinoma can be separated into Barrett's adenocarcinoma and cardiac adenocarcinoma, with frequent similarities observed. Barrett's adenocarcinoma is likely to be of gastric origin in terms of its premalignant background, risk factors, and stem cell regulators. Recent comprehensive genomic analyses suggest that immunotherapy may be essential for high‐level microsatellite instability (MSI‐H)‐ and Epstein‐Barr virus (EBV)‐associated subtypes, and against the immunosuppressive phenotype in genomically stable (GS) subtypes, in the treatment of EGJ and gastric adenocarcinoma. Although the chromosomal instability (CIN) subtype dominates EGJ adenocarcinoma, there is still a need to investigate the other molecular subtypes and their targets. Because of the distinctive characteristics of tumor location of EGJ adenocarcinoma, we also described the results of a multicenter cohort study of EGJ adenocarcinoma, comparing Siewert type I (distal esophagus), II (cardia of the stomach), and III (subcardia) tumors. We show that type I tumors were frequently accompanied by Barrett's esophagus (78%, P < .0001), with a significantly unfavorable outcome (multivariate EGJ‐cancer‐specific mortality hazard ratio = 1.81, 95% CI, 1.06‐2.97; P = .031). In addition, over half (56%) of these cases experienced disease recurrence in the lymph nodes. Our findings suggest that Barrett's adenocarcinoma may be an aggressive phenotype of EGJ adenocarcinoma due to the potential risk of tumor spread through the complex lympho‐vascular network of the esophagus.

Association of programmed death ligand 1 expression with prognosis among patients with ten uncommon advanced cancers.

Aim:PD-L1 expression and high levels of microsatellite instability (MSI-H) may predict response to checkpoint inhibitors, but their prevalence and prognostic value are unknown in many cancers.Methods:We retrospectively evaluated PD-L1 combined positive score (CPS) and MSI-H and their association with clinical outcomes among patients with ten advanced uncommon cancers.Results:398 of 426 patients (93%) had a valid PD-L1 result; most (242; 61%) had CPS ≥1. Prevalence of MSI-H tumors was 8/360. Median overall survival was shorter among patients with PD-L1 CPS ≥1 tumors after first-line treatment (23.0 vs 39.7 months, p = 0.014).Conclusion:PD-L1 was commonly expressed in solid tumors, and CPS ≥1 was associated with shorter overall survival. Prevalence of MSI-H was low.

Molecular-guided therapy for disseminated cervical cancer: present and future

Сervical cancer is recognized as one of the leaders in mortality from gynecological oncological diseases. The incidence and mortality from cervical cancer over the past 10 years remained at a consistently high level. For a long time, the only treatment option for metastatic and/or recurrent cervical cancer was cytotoxic chemotherapy, but its results remained extremely unsatisfactory: the 5-year overall survival rate was about 12%. This article is devoted to a review of the current possibilities of targeted and immunotherapy of metastatic and/or recurrent cervical cancer. We reviewed the most recent studies in the field of the effectiveness of antiangiogenic therapy including a critical and detailed analysis of the results of the GOG-240 phase III study. The data of modern literature in the field of immunotherapy using PD-1 / PD-L1 signaling pathway inhibitors in metastatic cervical cancer has been studied. It was found that a significant number of patients (34-95%) showed increased expression of PD-L1 in the tumor tissue, and 3-6% of patients showed a high level of microsatellite instability (MSI) in the tumor, which reveals the possibility of immunotherapy for this disease. We also conducted a review of ongoing clinical studies on the use of targeted and immunotherapy of advanced cervical cancer and the prospects for changing the “landscape” of treatment for this disease were assessed. On the example of a clinical case of treatment of a real patient, the possibilities of modern targeted and immunotherapy of metastatic cancer of the cervix uteri were analyzed, which gave a possibility to ensure long-term survival for the patient with an initially poor prognosis.

P-345 Evaluation of a fully automated Idylla test system for microsatellite instability in a cohort of Spanish patients with colorectal carcinoma in a single institution

Approximately 12-15% of all CRCs are associated with defects in the DNA MMR pathway. CRC patients whose tumors exhibit high-level microsatellite instability (MSI-H) have an increased probability of LS and these tumors are sensitive to immune checkpoint blockade with anti-ICK inhibitors. dMMR is defined as the loss of any protein by IHC. There is an excellent (but not perfect) correlation between IHC and PCR. Decisions about which screening test to use depend primarily on the availability of resources and expertise.

Microsatellite instability and mismatch repair protein expressions in lymphocyte-predominant breast cancer.

The frequency of microsatellite instability (MSI) is reportedly extremely low in breast cancer, despite widespread clinical expectations that many patients would be responsive to immune‐checkpoint inhibitors (ICI). Considering that some triple‐negative breast cancers (TNBC) responded well to ICI in a clinical trial and that a high density of tumor‐infiltrating lymphocytes (TILs) is frequently observed in other cancers with high levels of microsatellite instability (MSI‐H), we hypothesized that some TNBC with a high density of TILs would be MSI‐H. Medullary carcinoma (MedCa) of the breast, a rare histological type, is characterized by a high density of TILs. Considering that MedCa of the colon is often MSI‐H, we suspected that MedCa in breast cancer might also include MSI‐H tumors. Therefore, we conducted MSI tests on such breast cancers with a high density of TILs. The MSI status of 63 TIL‐high TNBC and 38 MedCa tumors, all from Asian women who had undergone curative surgery, were determined retrospectively. DNA mismatch repair (MMR) proteins and PD‐L1 expression were also investigated immunohistochemically. All samples were microsatellite stable, being negative for all microsatellite markers. TIL‐high TNBC with low MLH1 protein had higher levels of PD‐L1 in stromal immune cells (P = .041). MedCa tumors showed significantly higher PD‐L1 expression in immune cells than in TIL‐high TNBC (<.001). We found that MSI‐H tumors were absent in TIL‐high breast cancers. Examination of MMR proteins, not a purpose of Lynch syndrome screening, may merit further studies to yield predictive information for identifying patients who are likely to benefit from ICI.

Expression of HTRA Genes and Its Association with Microsatellite Instability and Survival of Patients with Colorectal Cancer.

HtrA proteases regulate cellular homeostasis and cell death. Their dysfunctions have been correlated with oncogenesis and response to therapeutic treatment. We investigated the relation between HtrA1-3 expression and clinicopathological, and survival data, as well as the microsatellite status of tumors. Sixty-five colorectal cancer patients were included in the study. The expression of HTRA1-3 was estimated at the mRNA and protein levels by quantitative PCR and immunoblotting. Microsatellite status was determined by high-resolution-melting PCR. We found that the HTRA1 mRNA level was higher in colorectal cancer tissue as compared to the unchanged mucosa, specifically in primary lesions of metastasizing cancer. The levels of HtrA1 and HtrA2 proteins were reduced in tumor tissue when compared to unchanged mucosa, specifically in primary lesions of metastasizing disease. Moreover, a decrease in HTRA1 and HTRA2 transcripts’ levels in cancers with a high level of microsatellite instability compared to microsatellite stable ones has been observed. A low level of HtrA1 or/and HtrA2 in cancer tissue correlated with poorer patient survival. The expression of HTRA1 and HTRA2 changes during colorectal carcinogenesis and microsatellite instability may be, at least partially, associated with these changes. The alterations in the HTRA1/2 genes’ expression are connected with metastatic potential of colorectal cancer and may affect patient survival.

Analysis of mutation detection of POLD1/pole in pan-cancer.

3142 Background: Previous studies proved that mutation of POLD1 and POLE elevates base-substitution mutations and lead to the elevation of tumor mutation burden (TMB). Other signature needs to explore to identify driver mutations in these two genes. Methods: Using gene-panel target-capture next generation sequencing, we analyzed the TMB and POLD1/POLE mutation in 17383 tumor tissue or plasma ctDNA samples from different patients. Results: Tumor mutation burdens were calculated of all the 17383 samples. According to the present research and our panel, we use 10 and 100 Mut/Mb to define hypermutation and ultra-hypermutation. Samples with hypermutation possessed 18.8% (n = 3268) and ultra-hypermutation possessed 0.3% (n = 58). In unselected, hypermutation and ultra-hypermutation group, POLD1 or/and POLE mutations were identified in 3.5% (n = 625), 56.1% (n = 32) and 87.9%(n = 372) samples. There were 0.5% (n = 81), 17.0% (n = 73) and 87.7%(n = 51) identified more than one mutation. These results showed that POLD1 or/and POLE mutations were enriched in samples with high TMB. We screened every known POLE and POLD1 driver mutations. There were 22 ultra-hypermutation samples identified these mutations, including A456P(3), P286R(10), V411L(6), M444K(1), S459F(1) in POLE and R1016H(1) in POLD1. Interestingly, all of them were identified in microsatellite stable (MSS) samples, which suggest that driver mutation may enriched in MSS samples. These already known driver mutation was not detect in 24 high-level microsatellite instability (MSI-H) and ultra-hypermutation samples. We further analyzed 10 POLD1/POLE mutations in other 5 MSS and ultra-hypermutation samples. POLE L424V was a pathogenic germline mutation but not defined as a driver mutation clearly before. POLE P286C had not been biochemically characterized but had different residue with P286R in the same position. Others had not been biochemically characterized (R232H, A234T, V945M, S1064I, Y467H in POLD1, D462N and R749Q, E1956D in POLE). These mutations were potential driver mutations and further research need to be support. Conclusions: We found that not only POLD1 or/and POLE mutations were enriched in samples with high TMB, but also driver mutations were enriched in microsatellite stable tumors. Further researches need to continue to identify more driver mutations of POLD1 and POLE.

Frequent CTNNB1 or PIK3CA Mutations Occurred in Endometrial Endometrioid Adenocarcinoma With High Levels of Microsatellite Instability and Loss of MSH2/MSH6 Expression.

DNA mismatch repair (MMR) proteins form 2 heterodimers-MutSα formed by MSH2 and MSH6, and MutLα by MLH1 and PMS2. In endometrial endometrioid adenocarcinomas, cases with MMR protein defect also usually harbor other recurrent genetic mutations of the neoplasm. However, it remains unknown whether defects of the 2 functionally different heterodimers are linked to mutations in different genes. We aimed to study the MMR protein expression, microsatellite instability (MSI), and other common genetic mutations of endometrial endometrioid adenocarcinoma. We investigated the MSI status of 107 endometrial endometrioid adenocarcinoma patients. MMR protein expression, and mutation of KRAS, CTNNB1, and PIK3CA were also evaluated by immunohistochemistry and sequencing. An overall 34.6% (37/107) of endometrial endometrioid adenocarcinomas were MSI-H. All MSI-H tumors exhibited loss of MMR protein expression (loss of MLH1, PMS2, MSH6, and MSH2 was noted in 22, 25, 12, and 7 cases, respectively). CTNNB1, PIK3CA, and KRAS mutation were present in 9, 7, and 7 MSI-H tumors. Compared with patients with loss of PMS2 and/or MLH1 expression, patients with loss of MSH6 and/or MSH2 expression were associated with higher frequencies of CTNNB1 mutation (P=0.036) and PIK3CA mutation (P=0.025). In MSI-H endometrial endometrioid adenocarcinomas, different types of MMR protein deficiency indicate different molecular genetic alterations.

Phase II study of nivolumab and relatlimab in advanced mismatch repair deficient (dMMR) cancers resistant to prior PD-(L)1 inhibition.

TPS839 Background: Cancers deficient in DNA mismatch repair (dMMR) are highly immunogenic tumors exhibiting high rates of response to immune checkpoint inhibitors targeting the programmed cell death-1 (PD-1)/PD-1 ligand (PD-L1) interaction. These tumors are characterized by high levels of microsatellite instability (MSI-H) and an exceptionally high tumor mutation burden, thought to underlie responsiveness to immunotherapy, with higher predicted immunogenicity of mutation-associated neoantigens. However, primary and acquired resistance are observed and diversity in responses is not fully explained by variations in mutation burden. Other immune checkpoints may be acting in parallel with PD-1/PD-L1. In particular, lymphocyte activation gene 3 (LAG3) mediates exhaustion of activated T cells and may have a role in resistance to PD-(L)1 inhibitors (PD-(L)1i); therefore, we hypothesized that the addition of LAG3 inhibitor (relatlimab) to the PD-1i nivolumab may overcome resistance in these tumors. Methods: Patients with advanced dMMR/MSI-H cancer who have progressive disease (by RECIST 1.1) during or within 6 months of PD-(L)1i containing therapy, and after at least 12 weeks of therapy, and meet other eligibility will be enrolled. All patients will receive nivolumab 480mg + relatlimab 160mg every 4 weeks until intolerance or progression, or up to a maximum of 2 years. The primary endpoint is objective response rate. Key secondary endpoints include safety, progression free and overall survival, and other response endpoints as measured by RECIST 1.1 and iRECIST criteria. Exploratory objectives will include analysis of the tumor microenvironment on biopsies obtained at baseline and on-treatment, analysis of T cell populations in the tumor and in the periphery and functional characterization of mutation-associated neoantigen-specific T cells. Studies of the microbiome will be conducted on stool and oral wash samples. Enrollment of 21 patients is planned. Clinical trial information: NCT03607890.

Nivolumab in real-life clinical practice

Purpose of the study . To evaluate the efficacy and tolerability of nivolumab in oncologic patients in real-life clinical seffings. Patients and methods . Analysis included 114 patients aged 26-96 years with melanoma ( n = 64), non-small cell lung carcinoma (NSCLC) ( n = 37) and metastatic colorectal cancer with high levels of microsatellite instability (MSI-H mCRC) ( n = 13), receiving immune checkpoint therapy with nivolumab (3 mg/kg every 14 days). All patients underwent comprehensive examination including CT/chest radiography, CT/MRI/ultrasound of abdominal organs or PET-CT of the whole body and other investigations if necessary. Efficacy of treatment was assessed after every 6 courses on treatment or in case of signs of clinical progression. Treatment response was assessed using iRECIST 1.1 criteria. Results . Among patients with metastatic melanoma positive for BRAF gene mutation, receiving immune therapy objective treatment response was registered in 13.6%, tumor control — in 27.2%. In the group of patients, negative for BRAF gene mutation objective response was achieved in 27.5%, tumor control — in 41.4% patients. None of mCRC patients in our group achieved objective response, stable disease was observed in 30.8% of patients, progression — in 38.5% and unconfirmed progression — in 7.7% of patients. In NSCLC group complete response was observed in 2.7%, partial response — in 2.7%, stabilization — in 27.1%, unconfirmed progression — in 5.4%, progression — in 29.7% of patients. Safety analysis revealed the following significant adverse reactions: thyroiditis (n = 3), pneumonitis of 3 grade (n = 1), hepatitis of 3 grade (n = 1) and arthritis of 2 grade (n = 1). In 4 patients adverse reactions required treatment delay and prescription of glucocorticoids. Conclusion . Nivolumab treatment in real-life clinical practice is associated with a lower prevalence of adverse events compared to the results of clinical trials.

Microsatellite Instability and Survival in Stage II Colorectal Cancer: A Systematic Review and Meta-analysis.

About 15-20% of colorectal cancers (CRCs) have deficiency in a mismatch repair (MMR) protein. MMR has a high level of microsatellite instability (MSI-H). We have conducted this review and meta-analysis to determine the prognostic role of MSI-H status in stage II CRC. We searched PubMed, EMBASE, The Cochrane Library, Web of Science, and SCOPUS for studies reporting data on overall survival (OS) and disease-free or relapse-free survival (DFS or RFS) for MSI-H compared to microsatellite stable (MSS) CRC. A total of 39 studies were analysed, including 12,110 patients. MSI-H status was associated with a significantly reduced risk of death (HR=0.64, 95%CI=0.52-0.8, p<0.01) and relapse (HR=0.59, 95%CI=0.45-0.77, p<0.01) in stage II CRC. MSI-H represents an important prognostic determinant in stage II CRC and may be considered when estimating the risk of recurrence in stage II CRC.

Prevalence of Lynch syndrome among patients with upper urinary tract carcinoma in a Japanese hospital-based population.

The prevalence of Lynch syndrome and the use of universal tumor screening to identify Lynch syndrome among unselected patients with upper urinary tract urothelial carcinoma, which is associated with Lynch syndrome, have not been closely investigated yet. A total of 166 tumors from 164 upper urinary tract urothelial carcinoma patients were tested for microsatellite instability and expression of mismatch repair proteins (MLH1, MHS2, MSH6 and PMS2) by immunohistochemistry. Genetic testing was performed for patients suspected of having Lynch syndrome. Clinicopathological factors, including familial and personal cancer history associated with mismatch repair deficiency, were evaluated. The frequency of high-level microsatellite instability and loss of at least one mismatch repair protein was 2.4% (4/164); the microsatellite instability and immunohistochemistry results showed complete concordance. Of these four patients, three were genetically proven to have Lynch syndrome, while the remaining one was highly suggestive for Lynch syndrome based on their personal cancer history. Univariate analysis showed that age<70years (P=0.04), ureter as the tumor location (P=0.052), previous history/synchronous diagnosis of colorectal cancer (P<0.01) and fulfillment of the criteria per the revised Bethesda guideline (P<0.01) tended to be or were significantly associated with high-level microsatellite instability/mismatch repair loss. The prevalence of Lynch syndrome among unselected upper urinary tract urothelial carcinoma patients was at least 1.8% in our study population. The screening efficacies of the microsatellite instability test and immunohistochemistry appear equivalent. Universal tumor screening may be a valid approach; however, selective screening methods that consider factors associated with mismatch repair loss/high-level microsatellite instability tumors require further investigation.

136 Usefulness of Magnifying Narrow-Band Imaging Endoscopy for the Diagnosis of Sessile Serrated Adenoma/Polyp With Dysplasia/Carcinoma

INTRODUCTION: Sessile serrated adenoma/polyp (SSA/P) is an early precursor lesion in the serrated neoplasia pathway, which results in BRAF-mutated colorectal carcinomas with high levels of microsatellite instability. Therefore, accurate diagnosis of SSA/P and its dysplastic components is endoscopically important. However, the usefulness of magnifying narrow-band imaging (NBI) endoscopy for SSA/Ps with dysplastic change has not yet been fully elucidated. The aim of this study was to verify the usefulness of magnifying NBI endoscopy for the diagnosis of SSA/P with dysplasia/carcinoma. METHODS: Among 939 endoscopically or surgically resected lesions pathologically diagnosed as SSA/P with or without dysplasia/carcinoma at Juntendo University Hospital (Tokyo, Japan) between 2011 and 2018, a total of 709 lesions had images available. These SSA/P lesions included 647 with no dysplasia (ND), 37 with low-grade dysplasia (LGD), 15 with high-grade dysplasia (HGD), and 10 with submucosal invasive carcinoma (SIC). We retrospectively evaluated magnifying NBI endoscopic findings using the Japan NBI Expert Team (JNET) system. RESULTS: The clinicopathological and endoscopic characteristics of the studied lesions are summarized in Table 1. The HGD and SIC lesions were associated with advanced age. All the lesions were more frequently located in the proximal colon. The SIC lesions were significantly larger than the ND and LGD lesions. All the lesions frequently exhibited endoscopic findings characteristic of SSA/P, such as mucus cap and Type II-Open pit pattern. As for the JNET classification of magnifying NBI endoscopy findings, all 709 lesions were type 1. Six hundred and eighteen (96%) ND lesions exhibited type 1 only, whereas 52 (84%) SSA/P with dysplasia/carcinoma lesions had a combination of type 1 and types 2A, 2B, or 3, corresponding to SSA/P and dysplasia/carcinoma, respectively (Figures 1 and 2). Furthermore, the JNET classification had high sensitivity (84%) and specificity (96%) for diagnosing SSA/P with dysplasia/carcinoma. CONCLUSION: Recently, the JNET was established and has proposed a universal NBI magnifying endoscopic classification of colorectal tumors. Our findings suggest that the use of magnifying NBI endoscopy using the JNET classification might be useful for the diagnosis of not only conventional colorectal tumors, but also SSA/P with dysplasia/carcinoma. This increased awareness may also improve the recognition of SSA/Ps with dysplasia or invasive carcinoma.

Detection of Microsatellite Instability Biomarkers via Next-Generation Sequencing.

A high level of microsatellite instability (MSI-H+) is an emerging predictive and prognostic biomarker for immunotherapy response in cancer. Recently, MSI-H+ has been detected in a variety of cancer types, in addition to the classical cancers associated with Lynch Syndrome. Clinical testing for MSI-H+ is currently performed primarily through traditional polymerase chain reaction (PCR) or immunohistochemistry (IHC) assays. However, next-generation sequencing (NGS)-based approaches have been developed which have multiple advantages over traditional assays. For instance, NGS has the ability to interrogate thousands of microsatellite loci compared with just 5-7 loci that are detected by PCR. In this chapter, we detail the biochemical and computational steps to detect MSI-H+ from analysis of paired tumor and normal samples through NGS. We begin with DNA extraction, describe sequencing library preparation and quality control (QC), and outline the bioinformatics steps necessary for sequence alignment, preprocessing, and MSI-H+ detection using the software tool MANTIS. This workflow is intended to facilitate more widespread usage and adaptation of NGS-powered MSI detection, which can be eventually standardized for routine clinical testing.

The spectrum of Lynch syndrome-associated germ-line mutations in Russia

Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome (LS), is a common cancer-predisposing syndrome. This study aimed to investigate the spectrum of germ-line mutations in Russian LS patients. LS-related mismatch repair (MMR) genes were analyzed in 16 patients, who were forwarded to genetic testing due to strong clinical features of LS and had high-level microsatellite instability (MSI-H) in the tumor (n = 14) or unknown MSI status (n = 2). In addition, 672 consecutive colorectal cancer (CRC) cases were screened for family history; 15 patients were younger than 50 years and reported 2 or more instances of LS-related cancers in 1st- or 2nd-degree relatives. Seven of these cases demonstrated MSI-H and therefore were subjected to DNA germ-line testing. Overall, 17/23 (74%) subjects carried LS-associated gene variants (MLH1: 10; MSH2: 4; MSH6: 2; PMS2: 1), with 2 alleles (MLH1 c.677G > T and MSH2 с.1906G > C) detected twice. Testing for recurrent mutations of 30 consecutive MSI-H CRCs led to the identification of 2 additional subjects with LS. The analysis of all relevant publications identified 28 unrelated LS patients presented in Russian medical literature and 3 unrelated Russian LS subjects described in international journals. Overall, 15/49 (31%) genetic defects revealed in Russian LS patients were represented by six recurrent alleles (MLH1: c.350C > T, c.677G > T, c.1852_1854del; MSH2: c.942+3A > T, c.1861C > T, с.1906G > C). We conclude that the founder effect for LS in Russia is seemingly less pronounced than the one for hereditary breast-ovarian cancer syndrome, however testing for recurrent LS mutations may be considered feasible in some circumstances.

Differences in gene expression profiling and biomarkers between histological colorectal carcinoma subsets from the serrated pathway.

To discern the differences in expression profiling of two histological subtypes of colorectal carcinoma (CRC) arising from the serrated route (serrated adenocarcinoma (SAC) and CRC showing histological and molecular features of a high level of microsatellite instability (hmMSI-H) both sharing common features (female gender, right-sided location, mucinous histology, and altered CpG methylation), but dramatically differing in terms of prognosis, development of an immune response, and treatment options. Molecular signatures of SAC and hmMSI-H were obtained by the use of transcriptomic arrays; quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were used to validate differentially expressed genes. An over-representation of innate immunity functions (granulomonocytic recruitment, chemokine production, Toll-like receptor signalling, and antigen processing and presentation) was obtained from this comparison, and intercellular cell adhesion molecule-1 (ICAM1) was more highly expressed in hmMSI-H, whereas two genes [those encoding calcitonin gene-related peptide-receptor component protein and C-X-C motif chemokine ligand 14 (CXCL14)] were more highly expressed in SAC. These array results were subsequently validated by qPCR, and by IHC for CXCL14 and ICAM1. Information retrieved from public databanks confirmed our findings. Our findings highlight specific functions and genes that provide a better understanding of the role of the immune response in the serrated pathological route and may be of help in identifying actionable molecules.

Transcriptome and Network Dissection of Microsatellite Stable and Highly Instable Colorectal Cancer.

Background:Colorectal cancer (CRC) is one of the most common cancers worldwide with high number of mortality every year. Microsatellite instability (MSI) is a considerable feature of CRC which affects prognosis and treatment. High level of MSI or MSI-high (MSI-H) colorectal cancer has better prognosis and immunotherapy response, while microsatellite stable (MSS) CRC has better response to 5-fluorouracil (5-FU)-based chemotherapy. More studies are needed, specifically on MSS CRC which has worse prognosis, to further reveal biological differences and similarities between MSS and MSI colorectal cancer, which may equip us with the knowledge to develop more promising therapeutic approaches to target both types or be more effective for each type. Methods:We aimed to find affected biological processes and their regulators in both type, MSS and MSI-H, of CRC; as well as reveal specific ones in each type. We applied meta- and network analysis on freely available transcriptome data in MSS and MSI-H colorectal cancer from gene expression omnibus (GEO) database to detect common differentially expressed genes (DEGs) and critical biological processes and predict their most significant regulators. Results:Our results demonstrate considerable up and downregulation in cell cycle and lipid catabolism processes, respectively; and introduced MYC and FOXM1 as two central and up-stream regulators of DEGs in both type of CRC. Chemokine-mediated processes displayed up-regulation in MSI-H type, while metastasis-related processes showed more activation in MSS CRC. Additionally, DACH1 and TP53 were detected as two important transcription factors that differentially expressed just in MSS and MSI-H, respectively. Conclusion:Our results can explain why MSI and MSS CRC display different immunotherapy response, prognosis, and metastasis feature. Moreover, our predicted up-stream regulators in the regulatory networks may be promising therapeutic targets.

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 features, diagnosis, and treatment of sessile serrated adenoma/polyp with dysplasia/carcinoma.

Sessile serrated adenoma/polyps (SSA/Ps) are early precursor lesions in the serrated neoplasia pathway, which results in BRAF-mutated colorectal carcinomas with not only high levels of microsatellite instability but also microsatellite stable. SSA/Ps with advanced histology, including cytological dysplasia or minimally invasive carcinomas, are important lesions because SSA/Ps are considered major contributors to "interval cancers" and these lesions can rapidly become dysplastic or invasive carcinomas. Clinicopathologically, SSA/Ps with dysplasia or invasive carcinoma were associated with advanced age, female sex, and proximal colon. Although SSA/Ps with submucosal invasive carcinoma were smaller and invaded less deeply into the submucosal layer than conventional tubular adenomas with submucosal invasive carcinoma, SSA/Ps with submucosal invasive carcinoma frequently had a mucinous component and exhibited a higher potential for lymphatic invasion and lymph node metastasis. In an SSA/P series, endoscopic characteristics, including (semi)pedunculated morphology, double elevation, central depression, and reddishness, may help accurately diagnose SSA/Ps with advanced histology. Removal of SSA/Ps with dysplasia or invasive carcinoma was recommended. Endoscopic treatment such as endoscopic mucosal resection or endoscopic submucosal dissection is useful for those lesions. However, surgical resection with lymph node dissection might be indicated when SSA/Ps with invasive carcinoma are endoscopically suspected, because these have the high risk of lymph node metastasis. Greater awareness may promote further research into improving the detection, recognition, and complete resection rates of SSA/Ps with dysplasia or invasive carcinoma and reduce the interval cancer rates.

Screening of colorectal cancer (CRC) patients for lynch syndrome (LS) emphasizes the need for public insurance coverage of genetic testing: Results of a national program by the Hellenic Society of Medical Oncology (HeSMO).

e13141 Background: Lynch Syndrome is associated with germline mutations in Mismatch Repair (MMR) genes ( MLH1, MSH2, MSH6, PMS2). CRC patients whose tumors exhibit high-level microsatellite instability (MSI-H) have an increased probability of LS. Although the diagnosis of LS has important implications for the patient and the family, germline genetic testing is not reimbursed by the Hellenic Public State Healthcare Services. To address this need HeSMO conducted a national program to screen and diagnose CRC patients with LS. Methods: All patients with CRC were eligible. Assessment for LS involved initially screening tumor tissue for the presence of MMR deficiency, either via molecular MSI testing or via immunohistochemistry (IHC) to detect the absence of one or more MMR proteins. Patients with an MMR-deficient tumor in the absence of a somatic cause (e.g. BRAF mutation or MLH1 promoter hypermethylation) underwent genetic counseling and germline testing to confirm a LS diagnosis. Results: From June 2017 to December 2018, 104 patients diagnosed with CRC were enrolled and tested. Median age of diagnosis was 58,5 years (range 32 - 89) and male-to-female ratio was 1.6:1. Fifty patients (48%) had tumors that exhibited the MSI-H phenotype. From the MSI-H tumors, 41 (82%) did not harbor the BRAF V600E mutation and 33 of them (80.5%) did not harbor an MLH1 promoter hypermethylation. Therefore, 33 patients were invited for genetic counseling and testing. Fifteen patients (45.45%) were diagnosed with LS: 6 ( 40 %) had a mutation in MLH1 (one of which had also a mutation in PMS2 gene), 4 (26.6%) in MSH6, 4 (26.6%) in MSH2 and 1 (6.6%) in PMS2. Conclusions: In our series, 30% of the CRC patients with MSI-H tumors were tested positive for LS. These results confirm the value of a universal screening program of CRC patients for LS. Hopefully, these results will convince the Hellenic Public State Healthcare Services to reimburse screening and germline genetic testing of CRC patients for LS.