Microsatellite Instability Testing Research Articles

Microsatellite Instability Testing and Prognostic Implications in Colorectal Cancer

Microsatellite Instability Testing and Prognostic Implications in Colorectal Cancer

Characterization of discordance between mismatch repair deficiency and microsatellite instability testing may prevent inappropriate treatment with immunotherapy.

In the Drug Rediscovery Protocol (DRUP), patients with cancer are treated based on their tumor molecular profile with approved targeted and immunotherapies outside the labeled indication. Importantly, patients undergo a tumor biopsy for whole-genome sequencing (WGS) which allows for a WGS-based evaluation of routine diagnostics. Notably, we observed that not all biopsies of patients with dMMR/MSI-positive tumors as determined by routine diagnostics were classified as microsatellite-unstable by subsequent WGS. Therefore, we aimed to evaluate the discordance rate between routine dMMR/MSI diagnostics and WGS and to further characterize discordant cases. We assessed patients enrolled in DRUP with dMMR/MSI-positive tumors identified by routine diagnostics, who were treated with immune checkpoint blockade (ICB) and for whom WGS data were available. Patient and tumor characteristics, study treatment outcomes, and material from routine care were retrieved from the patient medical records and via Palga (the Dutch Pathology Registry), and were compared with WGS results. Initially, discordance between routine dMMR/MSI diagnostics and WGS was observed in 13 patients (13/121; 11%). The majority of these patients did not benefit from ICB (11/13; 85%). After further characterization, we found that in six patients (5%) discordance was caused by dMMR tumorsthat did not harbor an MSI molecular phenotype by WGS. In six patients (5%), discordance was false due to the presence of multiple primary tumors (n = 3, 2%) and misdiagnosis of dMMR status by immunohistochemistry (n = 3, 2%). In one patient (1%), the exact underlying cause of discordance could not be identified. Thus, in this group of patients limited to those initially diagnosed with dMMR/MSI tumors by current routine diagnostics, the true assay-based discordance rate between routine dMMR/MSI-positive diagnostics and WGS was 5%. To prevent inappropriate ICB treatment, clinicians and pathologists should be aware of the risk of multiple primary tumors and the limitations of different tests. © 2024 The Pathological Society of Great Britain and Ireland.

A Prospective Study to Evaluate the Prevalence of Microsatellite Instability in Endometrial Carcinoma by using Immunohistochemistry for Mismatch Repair Proteins as a Surrogate Marker

Abstract Aim Use of immunohistochemistry for mismatch repair (MMR) proteins to identify the prevalence of microsatellite instability (MSI) in cases of endometrial carcinoma and its subsequent correlation with various histopathological parameters. Materials and Methods The expression of MMR proteins, viz PMS2, MLH1, MSH2, and MSH6, were assessed in 114 endometrial cancer cases by immunohistochemistry using Dako EnVision FLEX system, on paraffin blocks of tumor tissue fixed in 10% formalin. Results We studied 114 endometrial cases for MMR protein expression, of which the majority were of endometrioid histologic subtype (n = 93, 81.6%), whereas the remainder comprised serous carcinoma (n = 12, 10.5%), clear cell carcinoma (n = 1, 0.9%), carcinosarcoma (n = 5, 4.4%), and dedifferentiated uterine carcinoma (n = 3, 2.6%). Twenty-one (18%) of these cases were found to be deficient for MMR proteins, of which 20 were of endometrioid histologic subtype and only 1 was dedifferentiated uterine carcinoma. Loss of MMR protein expression occurred in pairs of either PMS2 and MLH1 or MSH2 and MSH6. Conclusion MSI is one of the major molecular pathways contributing to tumorigenesis in endometrial carcinomas. Immunohistochemistry for MMR proteins is a highly sensitive and cost-effective alternative for molecular testing for MSI. It is also a great tool for screening patients for Lynch syndrome. Immunohistochemical testing for MMR should be offered to all patients of endometrial cancers.

Poorly differentiated mucinous carcinoma of the ascending colon complicated by bilateral ovarian mature cystic teratomas in a 17-year-old female patient: a case report

BackgroundColorectal cancer (CRC) is one of the most common cancers worldwide, and screening colonoscopy has led to a decreasing incidence rate. However, the incidence of CRC is increasing among young people, especially adolescents and young adults (AYAs) who are not routinely screened. Although CRC is the fourth most common cancer among AYAs, it is extremely rare. In younger patients, CRC is often diagnosed later, and the proportion of patients with advanced CRC is higher than that in older patients. We herein present a case of poorly differentiated mucinous carcinoma of the ascending colon complicated by bilateral ovarian mature cystic teratomas (MCTs) in an AYA.Case presentationA 17-year-old female patient presented with a chief complaint of abdominal pain and diarrhea that had persisted for more than 3 years. Colonoscopy revealed circumferential wall thickening of the ascending colon, and colonic biopsy revealed a mucous mass and findings of adenocarcinoma, predominantly signet ring cell carcinoma. Abdominal computed tomography (CT) and pelvic magnetic resonance imaging (MRI) showed bilateral ovarian tumors. Laparoscopic right hemicolectomy and enucleation of bilateral ovarian tumors were performed. Although the ascending colon cancer formed a large mass, there were no signs of peritoneal dissemination or direct invasion to the surrounding organs. Microscopically, the ascending colon was a poorly differentiated mucinous carcinoma with signet ring cell carcinoma and lymph node metastasis (9/42). The ovarian tumors were diagnosed as MCTs without any malignant components. The pathological diagnosis was ascending colon cancer (pT4aN2bM0, pStage IIIC) and bilateral ovarian MCTs. Microsatellite instability (MSI) testing was negative, and there were no gene mutations in either RAS or BRAF. Postoperative adjuvant chemotherapy with oxaliplatin and 5-FU was started.ConclusionsWe presented a case of locally advanced ascending colon cancer in a 17-year-old female patient. CRC rarely occurs in AYAs. However, the incidence has gradually increased in recent years. It should be considered as a differential diagnosis for young patients with long-term abdominal symptoms of unknown cause.

Real-world prevalence of microsatellite instability testing and related status in women with advanced endometrial cancer in Europe.

To assess the real-world prevalence of microsatellite instability (MSI)/mismatch repair (MMR) testing and related tumor status in recurrent/advanced endometrial cancer patients in Europe. Data were from two multi-center, retrospective patient chart review studies conducted in the United Kingdom, Germany, Italy, France and Spain: The Endometrial Cancer Health Outcomes-Europe-First-Line (ECHO-EU-1L) study and the ECHO-EU-Second-Line (ECHO-EU-2L) study. ECHO-EU-1L included recurrent/advanced endometrial cancer patients who received first-line systemic therapy between 1/JUN/2016 and 31/MAR/2020 after recurrent/advanced diagnosis. ECHO-EU-2L included patients with recurrent/advanced endometrial cancer who progressed between 1/JUN/2016 and 30/JUN/2019 following prior first-line systemic therapy. Data collected included patient demographics, MSI/MMR tumor testing and results, and clinical/treatment characteristics. ECHO-EU-1L included 242 first-line patients and ECHO-EU-2L included 475s-line patients. For all patients, median age at recurrent/advanced diagnosis was 69years, roughly half had endometrioid carcinoma histology and over 75% had Stage IIIB-IV disease at initial diagnosis. The prevalence of MSI/MMR testing in the first-line and second-line cohorts was similar (36.4 and 34.9%, respectively). Among those tested, a majority had non-MSI-high/MMR proficient tumors (80.7 and 74.7% among first- and second-line patients, respectively). About 15% had MSI-high/MMR deficient tumors in both cohorts, and a few patients had discordant results (3.4 and 10.8% among first- and second-line patients, respectively). Prior to the approvals of biomarker-directed therapies for recurrent/advanced endometrial cancer patients in Europe, there were low MSI/MMR testing rates for these patients of just over one-third. Given the availability of biomarker-directed therapies, increased MSI/MMR testing may help inform treatment decisions for recurrent/advanced endometrial cancer patients in Europe.

Microsatellite instability and mismatch repair protein deficiency: equal predictive markers?

Current clinical guidelines recommend mismatch repair (MMR) protein immunohistochemistry (IHC) or molecular microsatellite instability (MSI) tests as predictive markers of immunotherapies. Most of the pathological guidelines consider MMR protein IHC as the gold standard test to identify cancers with MMR deficiency and recommend molecular MSI tests only in special circumstances or to screen for Lynch syndrome. However, there are data in the literature which suggest that the two test types may not be equal. For example, molecular epidemiology studies reported different rates of deficient MMR (dMMR) and MSI in various cancer types. Additionally, direct comparisons of the two tests revealed relatively frequent discrepancies between MMR IHC and MSI tests, especially in non-colorectal and non-endometrial cancers and in cases with unusual dMMR phenotypes. There are also scattered clinical data showing that the efficacy of immune checkpoint inhibitors is different if the patient selection was based on dMMR versus MSI status of the cancers. All these observations question the current dogma that dMMR phenotype and genetic MSI status are equal predictive markers of the immunotherapies.

A radiomics signature derived from CT imaging to predict MSI status and immunotherapy outcomes in gastric cancer: a multi-cohort study.

Accurate microsatellite instability (MSI) testing is essential for identifying gastric cancer (GC) patients eligible for immunotherapy. We aimed to develop and validate a CT-based radiomics signature to predict MSI and immunotherapy outcomes in GC. This retrospective multicohort study included a total of 457 GC patients from two independent medical centers in China and The Cancer Imaging Archive (TCIA) databases. The primary cohort (n = 201, center 1, 2017-2022), was used for signature development via Least Absolute Shrinkage and Selection Operator (LASSO) and logistic regression analysis. Two independent immunotherapy cohorts, one from center 1 (n = 184, 2018-2021) and another from center 2 (n = 43, 2020-2021), were utilized to assess the signature's association with immunotherapy response and survival. Diagnostic efficiency was evaluated using the area under the receiver operating characteristic curve (AUC), and survival outcomes were analyzed via the Kaplan-Meier method. The TCIA cohort (n = 29) was included to evaluate the immune infiltration landscape of the radiomics signature subgroups using both CT images and mRNA sequencing data. Nine radiomics features were identified for signature development, exhibiting excellent discriminative performance in both the training (AUC: 0.851, 95%CI: 0.782, 0.919) and validation cohorts (AUC: 0.816, 95%CI: 0.706, 0.926). The radscore, calculated using the signature, demonstrated strong predictive abilities for objective response in immunotherapy cohorts (AUC: 0.734, 95%CI: 0.662, 0.806; AUC: 0.724, 95%CI: 0.572, 0.877). Additionally, the radscore showed a significant association with PFS and OS, with GC patients with a low radscore experiencing a significant survival benefit from immunotherapy. Immune infiltration analysis revealed significantly higher levels of CD8 + T cells, activated CD4 + B cells, and TNFRSF18 expression in the low radscore group, while the high radscore group exhibited higher levels of T cells regulatory and HHLA2 expression. This study developed a robust radiomics signature with the potential to serve as a non-invasive biomarker for GC's MSI status and immunotherapy response, demonstrating notable links to post-immunotherapy PFS and OS. Additionally, distinct immune profiles were observed between low and high radscore groups, highlighting their potential clinical implications.

Microsatellite instability is highly prevalent in older patients with colorectal cancer.

Clinical guidelines suggest screening of colorectal cancer (CRC) for microsatellite instability (MSI). However, microsatellite instability-high (MSI-H) CRC is not rare in older patients. This study aimed to investigate the prevalence of MSI-H CRC in an unselected population in an age-based manner. A retrospective analysis of data from patients undergoing radical surgery for CRC was performed. Only cases with results from MSI testing using immunochemistry (IHC) were analyzed. Age-based analyses were performed using two cut-off ages: 50 years. as stated in Amsterdam II guidelines, and 60 years. as outlined in the revised Bethesda criteria. The study population included 343 (146 female and 197 male) patients with a median age of 70 years (range 21-90 years). The prevalence of MSI-H tumors in the entire cohort was 18.7%. The prevalence of MSI-H CRC was 22.5% in the group ≤50 years vs. 18.2% in the group >50 years using the age limit in the Amsterdam II guidelines. MSI-H CRC was present in 12.6% of the group aged ≤60 years compared to 20.6% in the control group >60 years. MSI screening of CRC based on age alone is associated with negative selection of a relevant number of cases. MSI-H CRC is also common in elderly patients, who may be negatively selected secondary to an age-based screening algorithm. Following the results of this study, screening based on clinical criteria should be omitted in favor of systematic screening as is already internationally practiced.

Multiparametric MRI subregion radiomics for preoperative assessment of high-risk subregions in microsatellite instability of rectal cancer patients: A multicenter study.

Microsatellite instability (MSI) is associated with treatment response and prognosis in patients with rectal cancer (RC). However, intratumoral heterogeneity limits MSI testing in patients with RC. We developed a subregion radiomics model based on multiparametric magnetic resonance imaging (MRI) to preoperatively assess high-risk subregions with MSI and predict the MSI status of patients with RC. This retrospective study included 475 patients (training cohort, 382; external test cohort, 93) with RC from two participating hospitals between April 2017 and June 2023. In the training cohort, subregion radiomic features were extracted from multiparametric MRI, which included T2-weighted, T1-weighted, diffusion-weighted, and contrast-enhanced T1-weighted imaging. MSI-related subregion radiomic features, classical radiomic features, and clinicoradiological variables were gathered to build five predictive models using logistic regression. Kaplan-Meier survival analysis was conducted to explore the prognostic information. Among the 475 patients (median age, 64 years [interquartile range, IQR: 55-70 years];304 men and 171 women), the prevalence of MSI was 11.16% (53/475). The subregion radiomics model outperformed the classical radiomics and clinicoradiological models in both training (area under the curve [AUC]=0.86, 0.72, and 0.59, respectively) and external test cohorts (AUC=0.83, 0.73, and 0.62, respectively). The subregion-clinicoradiological model combining clinicoradiological variables and subregion radiomic features performed the optimal, with AUCs of 0.87 and 0.85 in the training and external test cohorts, respectively. The 3-year disease-free survival rate of MSI groups predicted based on the model was higher than that of the predicted microsatellite stability (MSS) groups in both patient cohorts (training, P=0.032; external test, P=0.046). We developed and validated a model based on subregion radiomic features of multiparametric MRI to evaluate high-risk subregions with MSI and predict the MSI status of RC preoperatively, which may assist in individualized treatment decisions and positioning for biopsy.

Comparison of standard mismatch repair deficiency and microsatellite instability tests in a large cancer series

BackgroundThe tumor-agnostic indication of immune checkpoint inhibitors to treat cancers with mismatch repair deficiency (dMMR)/microsatellite instability (MSI) increased the demand for such tests beyond Lynch syndrome. International guideline recommendations accept immunohistochemistry (IHC) for dMMR or molecular techniques (PCR or NGS) for MSI status determinations considering the two tests are equal, although there are scattered reports contradicting to this presumption.Materials and methodsHere we have directly compared four protein MMR immunohistochemistry (IHC) to MSI Pentaplex PCR test in a large cancer patient cohort (n = 1306) of our diagnostic center where the two tests have been run parallel in 703 cases.ResultsIn this study we have found a high discrepancy rate (19.3%) of the two tests which was independent of the tumor types. The MSI PCR sensitivity for MMR IHC status was found to be very low resulting in a relatively low positive and negative predicting values. As a consequence, the correlation of the two tests was low (kappa < 0.7). During analysis of the possible contributing factors of this poor performance, we have excluded low tumor percentage of the samples, but identified dMMR phenotypes (classic versus non-classic or unusual) as possible contributors.ConclusionAlthough our cohort did not include samples with identified technical errors, our data strongly support previous reports that unidentified preanalytical factors might have the major influence on the poor performance of the MSI PCR and MMR IHC. Furthermore, the case is open whether the two test types are equally powerful predictive markers of immunotherapies.

Clinicopathological features and prognoses in younger and older patients with mismatch repair defects colorectal cancer: a retrospective comparative cohort study.

Microsatellite instability-high (MSI-H) is an important biomarker for predicting the effects of immune checkpoint inhibitors (ICIs) in colorectal cancer (CRC) patients. However, due to the low mutation rate of MSI-H/deficient mismatch repair (dMMR) in the overall population, some doctors are of the view that testing this indicator increases the burden on patients, and consequently some patients fail to receive the most beneficial treatment methods. In order to provide testing criteria for younger patients with a higher proportion of MSI-H, we designed this retrospective controlled study. A retrospective analysis was conducted of 1,901 patients who were admitted to the Affiliated Cancer Hospital of Zhengzhou University from January 2017 to December 2019 and underwent CRC-related gene testing. For this analysis, 100 patients aged 40 or younger are defined as the young group, and 305 patients aged 71 and older but younger than 80 are defined as the elderly group. We included patients who met the following criteria: (I) underwent preoperative colonoscopy or gastroscopy and were diagnosed with CRC; (II) received perioperative adjuvant therapy; (III) underwent curative surgery for CRC. Each patient was followed up from the time of surgery until April 30, 2023, or death, with follow-up visits scheduled every 3 months for the first 2 years after surgery, and every 6 months thereafter. Clinical characteristics such as age, gender, body mass index (BMI), tumor depth (T), number of metastatic lymph nodes (N), distant metastasis (M), tumor, node, metastasis (TNM) stage, extent of surgical resection, tumor size, tumor location, differentiation grade, and carcinoembryonic antigen (CEA) levels were collected. The microsatellite instability (MSI) status was analyzed using fluorescence in situ hybridization (FISH). In young CRC patients, the proportion of MSI-H is higher than in elderly CRC patients (33% vs. 10.16%, P<0.001). The proportion of poorly differentiated tumors is also higher in young CRC patients compared to elderly CRC patients (53% vs. 31.15%, P<0.001). However, there were no significant differences in clinical characteristics between young and elderly CRC patients. In terms of prognosis, survival analysis of the young group showed that MSI status [hazard ratio (HR) =0.26, 95% confidence interval (CI): 0.08-0.88, P=0.03], TNM staging (HR =3.84, 95% CI: 1.38-10.71, P=0.010) were associated with the prognosis of CRC patients. The mutation rate of MSI-H is higher in young CRC patients compared to older. Our study further confirms that MSI-H can serve as a favorable prognostic marker for CRC patients. This finding may provide valuable guidance for clinicians in terms of prognosis assessment and treatment selection. If feasible, we hope that MSI testing can be performed for all CRC patients to enable targeted testing, with particular attention to monitoring the MSI status in young patients. This will aid clinicians in selecting appropriate treatment strategies for these patients.

Clinical utility of upfront circulating tumor DNA (ctDNA) genotyping to guide first-line therapy in patients (pts) with metastatic colorectal cancer (mCRC): A GOZILA substudy.

157 Background: The clinical utility of upfront ctDNA genomic profiling is not established in treatment (tx)-naïve pts with mCRC. Methods: GOZILA is a nationwide plasma genomic profiling study using Guardant360 CDx for advanced solid tumors. We assessed ctDNA molecular profile and its association with treatment efficacy in pts with mCRC who were enrolled in GOZILA from January 2018 to July 2022 and underwent ctDNA genotyping before initiation of first-line systemic tx. ctDNA fraction was defined as the maximum variant allelic frequency of somatic alteration and pts were classified into three groups based on ctDNA fraction: low (&lt;1%), middle (≥1% and &lt;10%) and high (≥10%) ctDNA fraction groups. Results: This study included 418 pts with mCRC receiving upfront ctDNA genotyping. Median turnaround time of ctDNA test was 7 days, comparable with standard-of-care (SOC) tissue RAS/BRAF testing (7 days) and microsatellite instability (MSI) testing (8 days). Pathogenic alterations were detected in 384 pts (92%), and concordance rates for RAS and BRAF mutation (mut) compared to SOC tissue-based testing were 91% and 97%, respectively. Based on biomarkers identified by ctDNA genotyping, 142 (40%) pts were treated with matched targeted tx: anti-EGFR antibody for RAS/BRAF wild-type (n=137), BRAF inhibitor for BRAF V600E mutation (n=4), and anti-PD-1 antibody for MSI high (n=1). Low, middle, and high ctDNA fraction groups included 87, 97 and 234 pts, respectively, and had significantly different median progression-free survival (PFS) (p&lt;0.01, table) and overall survival (OS) (p&lt;0.01, table), respectively. In 13 pts who repeated ctDNA test before second-line tx, those with elevated ctDNA fraction compared to upfront ctDNA had significantly shorter PFS (median, 3.8 vs. 8.1 months; HR, 5.7, 95% CI, 0.9 to 35.1) and OS (median, 8.2 vs. 17.4 months; HR, 11.3, 95% CI, 1.2 to 105.9) of second-line tx that those with not elevated ctDNA fraction. Conclusions: Upfront ctDNA genotyping successfully identified actionable genomic alterations in pts with mCRC. ctDNA fraction in upfront ctDNA was significantly associated with efficacy of first-line tx and ctDNA fraction monitoring may be useful in determination of subsequent tx. [Table: see text]

Consistency and heterogeneity of microsatellite instability (MSI) status in paired biopsy and surgical specimens of colorectal cancer: A necessity for MSI reassessment after treatment?

149 Background: Microsatellite instability (MSI) plays a crucial role as a cancer immunotherapy and prognosis biomarker, making accurate MSI detection essential. However, currently, there is still a lack of available data on the impact of neoadjuvant therapy on MSI status, as well as validated data on standardized methods for MSI testing in small biopsy samples. The study aimed to investigate the concordance of MSI status between paired biopsy and surgical samples, as well as the impact of neoadjuvant therapy on MSI status using a novel MSI next-generation sequencing (MSI-NGS) detection panel. Methods: A total of 137 colorectal cancer (CRC) patients were enrolled for this study, of whom 116 with paired biopsy and surgical samples were analyzed. A custom MSI-NGS panel was employed and its performance was compared to MSI polymerase chain reaction (MSI-PCR), which served as the gold standard. Results: Out of the 116 cases, 112 patients showed consistent MSI status between biopsy and surgical samples, with an overall accuracy of 97% regardless of the detection method used. In the cases with MSI discrepancy (6 cases), 83% (5/6) of the patients showed a transition from MSS to MSI-H from biopsy to surgery. Interestingly, all eight patients who received neoadjuvant chemotherapy maintained an unchanged MSI status. However, in one patient who received adjuvant treatment and underwent a repeat biopsy after surgery, the MSI status exhibited alterations. Further analysis of clonal evolution revealed that this heterogeneity stemmed from the disappearance of the original clones and the emergence of new clones. Additionally, the NGS panel exhibited strong concordance with MSI-PCR and high accuracy, sensitivity and specificity with an AUC of 0.942 after rigorous validation. Conclusions: The study revealed a high concordance in MSI status between paired biopsy and surgical samples by employing a custom MSI-NGS panel for MSI status detection, providing reliable basis for further research in this field. Moreover, neoadjuvant chemotherapy seemed to have no impact on MSI status in our study, whereas postoperative adjuvant chemotherapy may influence changes in MSI status, highlighting the necessity of reevaluating MSI status after surgery. The findings also underscore the potential of NGS-based MSI detection as a valuable tool for clinical decision-making.

Hereditary Colorectal Cancer in Brunei Darussalam

Introduction: Hereditary colorectal cancers (CRC) are associated with early age of disease onset and high risks of developing other cancers. In this study, we estimate the prevalence of hereditary CRC over a 6-year period, and report the socio-demographics and clinical profile of patients in Brunei Darussalam. Methods: A retrospective study of data from 146 patients diagnosed with CRC from January 2017 to December 2022 was obtained from The Brunei Cancer Centre. Suspected or confirmed hereditary CRC patients were flagged from the 146 cases based on microsatellite instability (MSI) assay testing, immunohistochemistry (IHC) four-panel staining on mismatch repair (MMR) genes MLH1, MSH2, MSH6, and PMS2, and BRAFV600E test results. Results: Among the 146 patients with CRC, 41.7% (n=61) patients underwent MSI testing where 7.5% (n=11) reported high instability in their microsatellite assay (MSI-H), of which 2 were associated with Lynch syndrome. Among the 11 patients with “suspected” or “confirmed” hereditary colorectal cancer, majority presented with abdominal pain prior to diagnosis (81.8%; n=9), Stage 2 cancer (36.4%; n=4), moderately differentiated tumour (72.7%; n=8), tumour located in caecum (36.4%; n=4) and all patients had surgery as first-line management, with more than half receiving chemotherapy (54.5%; n=6). Conclusion: 7.5% of patients of CRC cases seen at a tertiary cancer centre over a 6-year period was found to have “suspected” or “confirmed” hereditary CRC. The lack of genetic testing performed in local settings may indicate that the actual prevalence may be higher.

An Innovative and Accurate Next-Generation Sequencing–Based Microsatellite Instability Detection Method for Colorectal and Endometrial Tumors

The detection of microsatellite instability (MSI) and mismatch repair (MMR) deficiency has become mandatory for most tumors in recent years, owing to the development of immune checkpoint inhibitors as a highly effective therapy for MMR deficiency/MSI tumors. The timely and efficient detection of MSI is valuable, and new methods are increasingly being developed. To date, MMR assessment has been performed using immunohistochemistry of the 4 MMR proteins and/or microsatellite stability/MSI using PCR, mostly using the pentaplex panel. The implementation of next-generation sequencing (NGS) for MSI analysis would improve the effectiveness at a lower cost and in less time. This study describes the development of 8 new microsatellites combined with a classification algorithm, termed “Octaplex CaBio-MSID” (for Cancérologie Biologique MSI Detection tool), to assess MSI using NGS. A series of 303 colorectal cancer and 88 endometrial cancer samples were assessed via MSI testing using NGS using the Octaplex CaBio-MSID algorithm. The sensitivity and specificity of Octaplex CaBio-MSID were 98.4% and 98.4% for colorectal cancers, and 89.3% and 100% for endometrial cancers, respectively. This new NGS-based MSI detection method outperforms previously published methods (ie, Idylla [Biocartis], OncoMate MSI Dx [Promega], and Foundation One CDx [Roche Foundation Medicine]). Although highly efficient, Octaplex CaBio-MSID requires validation in a larger independent series of different tumor types.

Evaluation of an eight marker-panel including long mononucleotide repeat markers to detect microsatellite instability in colorectal, gastric, and endometrial cancers

BackgroundAccurate determination of microsatellite instability (MSI) status is critical for optimal treatment in cancer patients. Conventional MSI markers can sometimes display subtle shifts that are difficult to interpret, especially in non-colorectal cases. We evaluated an experimental eight marker-panel including long mononucleotide repeat (LMR) markers for detection of MSI.MethodsThe eight marker-panel was comprised of five conventional markers (BAT-25, BAT-26, NR-21, NR-24, and NR-27) and three LMR markers (BAT-52, BAT-59 and BAT-62). MSI testing was performed against 300 specimens of colorectal, gastric, and endometrial cancers through PCR followed by capillary electrophoresis length analysis.ResultsThe MSI testing with eight marker-panel showed 99.3% (295/297) concordance with IHC analysis excluding 3 MMR-focal deficient cases. The sensitivity of BAT-59 and BAT-62 was higher than or comparable to that of conventional markers in gastric and endometrial cancer. The mean shift size was larger in LMR markers compared to conventional markers for gastric and endometrial cancers.ConclusionsThe MSI testing with eight maker-panel showed comparable performance with IHC analysis. The LMR markers, especially BAT-59 and BAT-62, showed high sensitivity and large shifts which can contribute to increased confidence in MSI classification, especially in gastric and endometrial cancers. Further study is needed with large number of samples for the validation of these LMR markers.

PATH-14. MSI GENETIC FINDINGS IN FAMILIAL TURCOT SYNDROME 1 ASSOCIATED TO REPRODUCTION FAILURE

Abstract The aim of this study was to report MSI genetic findings in a three-generation Tunisian pedigree of Turcot syndrome 1 (TS1), characterized by an uncommon association with infertility and child mortality. Microsatellite instability testing and genetic counseling were offered to affected members and their young relatives, to provide optimal clinical and preventive care. The index case of our Tunisian pedigree was a 38-year-old female, in whom histologic assessment of endoscopic specimens through a colorectal adenoma resection during screening colonoscopy, showed a tubular adenoma of the lower rectum with low-grade intraepithelial neoplasia. The screening procedure was conducted because her two brothers, 58 and 60 years old, harbored respectively glioblastoma multiforme and colon adenocarcinoma. The first brother exhibited an intracranial hypertension syndrome and a left hemiplegia leading to the diagnosis of a brain tumor. Whereas the second brother manifested diarrhea and intestinal colic that were investigated by colonoscopy. Histologic assessment of endoscopic specimens through a right preangular budding formation showed a well-differentiated liberkhunian adenocarcinoma that was treated by a right hemicolectomy. Genetic assessment at the germinal and somatic levels was conducted for the three affected patients using conventional microsatellite instability (MSI) testing methods. Molecular analysis determined MSI status of the tumors and classified them into stable types (MSS) without any mutation or aberrant expression of MLH1, MSH2, MSH6, and PMS2 genes. Familial history revealed, at the first generation, a consanguineous couple who lost several children at a young age. This couple gave birth to eight children, three of whom were infertile, three affected by MMS TS1 and two healthy. The third generation consists of 15 children, so far, without any tumors. Genetic counselling for TS remains difficult because of the rarity of the condition, its shifting definition over the years, and its genetic and phenotypic heterogeneity.

Validation of MSIntuit as an AI-based pre-screening tool for MSI detection from colorectal cancer histology slides

Mismatch Repair Deficiency (dMMR)/Microsatellite Instability (MSI) is a key biomarker in colorectal cancer (CRC). Universal screening of CRC patients for MSI status is now recommended, but contributes to increased workload for pathologists and delayed therapeutic decisions. Deep learning has the potential to ease dMMR/MSI testing and accelerate oncologist decision making in clinical practice, yet no comprehensive validation of a clinically approved tool has been conducted. We developed MSIntuit, a clinically approved artificial intelligence (AI) based pre-screening tool for MSI detection from haematoxylin-eosin (H&E) stained slides. After training on samples from The Cancer Genome Atlas (TCGA), a blind validation is performed on an independent dataset of 600 consecutive CRC patients. Inter-scanner reliability is studied by digitising each slide using two different scanners. MSIntuit yields a sensitivity of 0.96–0.98, a specificity of 0.47-0.46, and an excellent inter-scanner agreement (Cohen’s κ: 0.82). By reaching high sensitivity comparable to gold standard methods while ruling out almost half of the non-MSI population, we show that MSIntuit can effectively serve as a pre-screening tool to alleviate MSI testing burden in clinical practice.

GLIOMA-01 GENETIC INVESTIGATIONS AND COUNSELING IN FAMILIAL MSS TURCOT SYNDROME ASSOCIATED TO INFERTILITY AND CHILD MORTALITY

Abstract The aim of this study was to report MSI genetic findings in a three-generation Tunisian pedigree of Turcot syndrome 1 (TS1), characterized by an uncommon association with infertility and child mortality. Microsatellite instability testing and genetic counseling were offered to affected members and their young relatives, to provide optimal clinical and preventive care. The index case of our Tunisian pedigree was a 38 year-old female, in whom histologic assessment of endoscopic specimens through a colorectal adenoma resection during screening colonoscopy, showed a tubular adenoma of the lower rectum with low-grade intraepithelial neoplasia. The screening procedure was conducted because her two brothers, 58 and 60 years old, harbored respectively glioblastoma multiforme and colon adenocarcinoma. The first brother exhibited an intracranial hypertension syndrome and a left hemiplegia leading to the diagnosis of a brain tumor. Whereas the second brother manifested diarrhea and intestinal colic that were investigated by colonoscopy. Histologic assessment of endoscopic specimens through a right preangular budding formation showed a well-differentiated liberkhunian adenocarcinoma that was treated by a right hemicolectomy. Genetic assessment at the germinal and somatic levels was conducted for the three affected patients using conventional microsatellite instability (MSI) testing methods. bMolecular analysis determined MSI status of the tumors and classified them into stable types (MSS) without any mutation or aberrant expression of MLH1, MSH2, MSH6, and PMS2 genes. Familial history revealed, at the first generation, a consanguineous couple who lost several children at a young age. This couple gave birth to eight children, three of whom were infertile, three affected by MMS TS1 and two healthy. The third generation consists of 15 children, so far, without any tumors. Genetic counselling for TS remains difficult because of the rarity of the condition, its shifting definition over the years, and its genetic and phenotypic heterogeneity.

Testing for deficient mismatch repair and microsatellite instability : Afocused update.

Testing to detect mismatch repair deficiency (dMMR) and high-grade microsatellite instability (MSI-H) has become an integral part of the routine diagnostic workup for colorectal cancer (CRC). While MSI was initially considered to be apossible indicator of ahereditary disposition to cancer (Lynch syndrome, LS), today the prediction of the therapy response to immune checkpoint inhibitors (ICI) is in the foreground. Corresponding recommendations and testing algorithms are available for use in primary diagnosis (reviewed in: Rüschoff etal. 2021).Given the increasing importance for routine use and the expanding indication spectrum of ICI therapies for non-CRCs, such as endometrial, small intestinal, gastric, and biliary tract cancers, an updated review of dMMR/MSI testing is presented. The focus is on the challenges in the assessment of immunohistochemical stains and the value of PCR-based procedures, considering the expanded ICI indication spectrum. Apractice-oriented flowchart for everyday diagnostic decision-making is provided that considers new data on the frequency and type of discordances between MMR-IHC and MSI-PCR findings, and the possible role of Next Generation Sequencing in clarifying them. Reference is made to the significance of systematic quality assurance measures (e.g., QuIP MSI portal and multicenter proficiency testing), including regular continued training and education.