Mutations In Mismatch Repair Proteins Research Articles

Glioma arising in the setting of mismatch repair deficiency-rare or are we missing it?

Germline mutations in mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2) can be mono-allelic or biallelic, resulting in a Lynch syndrome (LS) or constitutional mismatch repair deficiency (CMMRD) syndrome respectively. Glioma arising in the setting of MMR deficiency is uncommon. We describe two pediatric patients with high-grade glioma (HGG) and associated MMR protein deficiency. On histomorphology both cases showed HGG with astrocytic morphology and prominent multinucleated tumor cells. On immunohistochemistry, the first case was negative for IDH1 p.R132H showed loss of ATRX and p53 positivity. The second case was positive for IDH1 p.R132H and p53, but showed retained expression of ATRX. The histomorphology in both cases and additionally IDH mutation with retained ATRX in the second case, prompted us to test for MMR protein deficiency which was carried out by immunohistochemistry (IHC). One case revealed an immunostaining pattern suggestive of CMMRD while the other was suggestive of LS. Both the cases showed good response to surgery and radio-chemotherapy in the follow-up available. Our cases highlight the importance of testing for MMR proteins by simple IHC, in the setting of appropriate clinical scenario, histopathological and immunohistochemical findings. The recognition of these tumors is extremely important to guide further treatment and prompt family screening.

Abstract PO-052: A multisystem approach doubles the number of patients referred for genetic testing and diagnosed with Lynch syndrome with equally success among ethnic/racial groups

Abstract Background: Lynch syndrome (LS) affects 1/279 individuals and accounts for 3-5% of all colorectal cancers (CRC). LS is due to germline mutations in mismatch repair (MMR) genes MLH1, MSH2, MSH6, or PMS2. Tumors exhibit MMR deficiency, expressed as loss of MMR protein expression on immunohistochemistry (IHC). A subset of sporadic tumors also has MMR deficiency due to inactivation of MLH1 via promoter methylation and about 2/3 have BRAFV600E mutations. Increased surveillance and chemoprevention reduce cancer incidence and mortality in LS. LS is largely underdiagnosed, particularly among minorities. Universal screening of CRC tumors through IHC is recommended in order to help identify patients for LS genetic testing. Nevertheless, even in programs that have implemented this, minority patients with MMR deficient tumors were found to be consistently under-referred mostly due to referral bias. We set up a strategy to increase LS and tackle disparities in cancer genetics (CG). Methods: This study reports on the analysis of universal CRC IHC testing for MMR expression, initially followed by BRAF V600E and later by MLH1 testing for loss of MLH1/PMS2 expression, from implementation (1/1012) until 1/1021. In 6/2015, a system was established where a designated Pathologist reviewed all results and a list of identified candidates for germline LS testing (abnormal MMR expression/wild type BRAF or methylation of MLH1) was sent to the CG program. After a two-week period, if no referral had been placed, a genetic counselor (GC) messaged the provider requesting a referral. The pathology side was fully automated in 9/2018 through the monitoring engine Repetitive Tasks Scheduling Engine (RTSE) that pulls data stored in the underlying relational database-Adaptive Server Enterprise, which is accessible to RTSE via a Java Database Connectivity API. This process automatically generates weekly emails that report all cases with suspicion criteria for LS to CG. Results: Since 1-2012, 1,433 patients with CRC underwent tumor testing and were included in this study: 78.5% non-Hispanic white (NHW); 12.2% African American (AA); 6.77% Hispanic (H). Prior to the interventions 25% of eligible patients were referred to CG and none among AA. Once the interventions were established, appropriate referrals prior to messaging the provider were 39.5% for NHW, 35.7% for AA, and 42.8% for H. As a result of the messages, referral rates increased to 80.5% (p=0.00) in NHW, 85.7% in AA (p=0.05), and 71.5% in H (ns). The total number of patients diagnosed with LS since universal testing started was 19: 2 prior to the interventions (0.8% of all CRC); 17 during the interventions (1.5% of all CRC). Conclusion: A systematic, automated, multi-system approach, that includes a targeted message to providers can double the number of appropriate referrals for genetic testing to rule out Lynch syndrome and resulted in almost twice the percentage of LS diagnosis with equal success among AA, H, and NHW. Citation Format: Vinit Singh, Amanda Ganzak, Peter Gershkovich, Joanna Gibson, Rosa M. Xicola, Xavier Llor. A multisystem approach doubles the number of patients referred for genetic testing and diagnosed with Lynch syndrome with equally success among ethnic/racial groups [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-052.

Reading between the lines: The interpretation of immunohistochemical staining for mismatch repair proteins and its effect on clinical decision making in endometrial cancer

Objective: Up to 5% of endometrial cancers (EC) are associated with germline mutations in mismatch repair (MMR) genes. Screening for Lynch syndrome (LS) may be performed using clinical screening guidelines, microsatellite instability testing, or immunohistochemical (IHC) staining for MMR proteins (MMRP). Under current College of American Pathology (CAP) guidelines, any positive IHC MMR staining should be reported as intact expression. However, tumors may exhibit partial expression of MMRP, so-called heterogenous staining.

Assessment of mismatch repair protein expression by immunohistochemistry in endometrial carcinomas with clinicopathological correlation: A study from Indian Tertiary Cancer Care Centre

Objectives: Endometrial carcinomas (EC) are known to be histologically and biologically heterogeneous, and their recent molecular characterization has highlighted their etiologic heterogeneity. The aim of the present study was to analyze mutations in mismatch repair (MMR) proteins in ECs by immunohistochemistry (IHC), and correlates the data with their pathological parameters. Material and Methods: The expression of MMR proteins was analyzed using IHC in VENTANA BENCHMARK XT system, on formalin-fixed paraffin-embedded tumor tissue. The study population included 102 newly diagnosed cases of ECs over a duration of 2 years. Results: On histopathologic subtyping, 85.1% of cases were of Type 1 EC, 9.8% were Type 2 EC, and 4.9% were malignant mixed Mullerian tumors. On IHC for MMR protein expression, 22 of 102 cases (21.6%) showed loss of one or more protein, and mean age of patients with deficient MMR (dMMR) was 59.6 years. All of these dMMR cases were of endometrioid subtype, forming 25.3% of EEC. The combined loss of MLH1 and PMS2 was the most common abnormality detected (50% of dMMR). On pathological correlation, 54.5% of dMMR cases were found to be of higher grade (grade 2/3; P = 0.002) and 68.2% were higher stage tumors (T1b and above; P < 0.0001). The lymph-vascular invasion was seen in 50% of dMMR cases (4 of 8 cases). Conclusion: Detecting MMR protein loss in ECs by IHC is an efficient, relatively simple, and economical method. It needs to be routinely performed in all cases of ECs. Studies are still underway to utilize it as a therapeutic modality using immunotherapy.

Mismatch Repair Proteins (MLH1, MSH2, MSH6, and PMS2) Immunohistochemical Expression and Microsatellite Instability in Endometrial Carcinoma

BACKGROUND: Endometrial cancer (EC) is the fourth most common female cancer worldwide constituting 7% of cancer in women. It is a disease of older, postmenopausal women. The most of these patients have an identifiable source of excess estrogen, while in a small subset the pathogenesis is related to mismatch repair abnormality and lynch syndrome (LC). Mismatch repair behave as tumor suppressors and the most clinically relevant include MLH1, MSH2, MSH6, and PMS2. mutations in mismatch repair (MMR) results in a strong mutator phenotype known as microsatellite instability, which is a hallmark of LC-associated cancers.
 AIM: The aim of the study was to study microsatellite instability in endometrial cancer using the immunohistochemical expression of mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2).
 MATERIAL AND METHODS: Sixty EC cases were studied using MLH-1, MSH-2, MSH-6, and PMS-2 immunohistochemistry and their expression was correlated with different clinicopathologic parameters.
 RESULTS: A statistically significant relationship exists between MMR immunohistochemistry (IHC) proteins and tumor grade. Intact MMR proteins profile was associated with the lower tumor grade (31.3% were Grade 1 and 46.9% were Grade 2). Combined loss of MLH1/PMS2, combined loss of MSH2/MSH6, and isolated loss of PMS2 were also associated with the lower tumor grade while isolated loss of MSH6 was associated with the high tumor grade. However, no statistically significant correlation was found between MMR IHC proteins expression and the age of patients; tumor histopathological types, or FIGO stage.
 CONCLUSION: A statistically significant correlation between the tumor grade of EC cases and the MMR IHC proteins was found. Further studies are recommended to assess correlation between MMR proteins defect and different clinicopathological parameters of endometrial carcinoma.

Loss of DNA mismatch repair proteins in prostate cancer.

Recent studies have suggested an increased risk of prostate cancer in men with Lynch syndrome driven by germline mutations in mismatch repair (MMR) genes. However, the incidence and clinical implication of MMR deficiency in sporadic prostate cancers remain poorly understood. We immunohistochemically stained for MLH1, MSH2, MSH6, and PMS2 in a set of tissue microarray consisting of 220 radical prostatectomy specimens and evaluated the relationship between loss of their expression and available clinicopathological features. MLH1, MSH2, MSH6, and PMS2 were lost in 2 (0.9%), 6 (2.7%), 37 (16.8%), and 27 (12.3%) prostate cancers, respectively. Loss of at least 1 MMR protein was identified in 50 (22.7%) cases. There were no statistically significant associations between MMR deficiency and patient age, family history of prostate cancer, Gleason score, or pT/pN stage. Nonetheless, the levels of preoperative prostate-specific antigen (PSA) were significantly (P = .015) higher in patients with MMR deficiency (mean ± SD: 9.12 ± 9.01 ng/mL) than in those without abnormal MMR (5.76 ± 3.17 ng/mL). There were 15 (6.8%) cases showing loss of at least 2 MMR proteins, which was not significantly associated with PSA level or tumor grade/stage. Additionally, 5 and 2 cases showed losses of at least 3 MMR proteins and all 4 proteins, respectively. Kaplan–Meier analysis revealed no significant associations between loss of MLH1 (P = .373), MSH2 (P = .348), MSH6 (P = .946), or PMS2 (P = .681), or at least 1 (P = .477), 2 (P = .486), or 3 (P = .352) MMR proteins and biochemical recurrence. Further analyses of the data on programmed death-ligand 1 (PD-L1) expression previously stained in the same set of tissue microarray demonstrated associations between loss of ≥2 MMR proteins and a higher rate of PD-L1 expression in cancer cells (17.2% vs 5.2%; P = .033) as well as between cases showing both loss of ≥1 MMR protein(s) and PD-L1 expression in tumor-infiltrating immune cells vs a higher risk of biochemical recurrence (P = .045). MMR protein loss was seen in a subset of prostate cancers. Interestingly, it was associated with significantly higher levels of PSA. Moreover, immunohistochemical detection of MMR proteins together with other proteins, such as PD-L1, might be helpful in predicting tumor recurrence following radical prostatectomy.

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.

Clinicopathologic Features of Mismatch Repair-Deficient Anaplastic Thyroid Carcinomas.

Background: Prior studies have reported mutations in mismatch repair (MMR) genes in a small subset of anaplastic thyroid carcinomas (ATC). The aim of this study was to identify MMR-protein-deficient (MMR-D) ATC and investigate their histopathologic features and clinical outcome. Methods: A cohort of 28 ATC diagnosed between 2003 and 2017 with tissue blocks available were evaluated. Immunohistochemistry for MMR proteins was performed to identify MMR-D tumors. Clinicopathologic features, molecular findings (determined by a targeted next-generation sequencing assay), and clinical outcome data for MMR-D tumors were recorded and compared to that of MMR-protein-intact (MMR-I) tumors. Results: There were four (14%) MMR-D ATC, all of which showed complete loss of MSH2 and MSH6 with intact expression of MLH1 and PMS2. Three of these tumors had MSH2 mutations and a hypermutated phenotype by next-generation sequencing. All four patients (two male; Mage at diagnosis = 64 years) presented with stage IVB disease (i.e., gross extrathyroidal extension or a lymph node metastasis at presentation). There were no differences in tumor size or rates of gross extrathyroidal extension, lymph node metastases, or positive resection margins between MMR-D and MMR-I ATC. Patients with MMR-D tumors were less likely to have distant metastatic disease at presentation (p = 0.035), although half did eventually develop distant metastases. MMR-D tumors were not histologically distinct. All four patients with MMR-D tumors lived for more than one year. One patient died of disease at 15 months, while the remaining three were alive at last follow-up, with survival of 19, 38, and 48 months. Patients with MMR-D ATC had significantly better survival compared to those with MMR-I tumors (p = 0.033), which was maintained when considering only patients with stage IVB disease at presentation (p = 0.030). Conclusion: MMR-D tumors comprised 14% of this ATC cohort. Although the findings must be interpreted with caution given the small number of MMR-D ATC in the cohort, the results suggest that MMR status may be prognostically significant in ATC.

Abstract 2916: The clonal evolution of glioblastoma

Abstract Background: Glioblastoma (GBM) is an aggressive cancer that often recurs despite multimodal therapy. Median survival is 12-15 months. Genomic profiling studies have shown marked tumor heterogeneity with distinct mutations among treated and untreated samples. The Cancer Genome Atlas (TCGA), revealed that mutations in TP53, CDKN2A, PTEN, EGFR and NF1 are predominant in untreated tumors. Of 19 patients who progressed on therapy, seven samples were hypermutated with mutations in mismatch repair proteins, mainly MSH6. We proposed to use the Cellecta Lentiviral-based tagging library, a novel model system to assess the role of intratumor heterogeneity (ITH) in the presumptive tumor-initiating fraction of primary GBM and in the development of resistance to temozolomide (TMZ). From a pool of 30,000,000 barcodes, the system enables the genetic integration of a unique barcode sequence into each cell. Each barcode can be quantitatively tracked via next-generation sequencing, allowing for dynamic monitoring of the subclonal architecture. Methods: GSC 272 and 627 (sensitive and resistant to TMZ) were derived from core biopsies of GBM patients. Cells were transduced with a lentiviral vector containing luciferase. Cells were expanded and infected with the Cellecta Lentiviral library. Multiplicity of infection was determined. Transduced cells were injected into B6.Cg-Foxn1nu/J mice brains using a guide screw system. Half of the mice were treated with TMZ via gavage at two weeks. Brain tumors were removed and total DNA was extracted. Barcode inserts were amplified and the Illumina Sequencing platform was used for barcode quantification. Additionally, whole exome sequencing was performed to assess mutation status. Results: Confirmation of luciferase signal has been performed using a Luciferase Reporter Assay. Multiplicity of infection was found to be 0.15 and 1 for GSC 6-27 and 272 respectively. Initial methylation studies showed GSC 272 to have methylation of MGMT while GSC 627 did not. There was no difference in OS in the TMZ Resistant (GSC 627) untreated vs. treated cohort (with a median OS of 55 days in both groups (N= 23 vs 25 respectively, P= 0.563). TMZ Sensitive (GSC 272) untreated mice did not survive as long as the treated cohort (N= 24 vs. 25, Median OS 43 vs. 206 days, P= 4.61e-09). Barcode and whole exome sequencing results is currently being analyzed. Conclusions: The Cellecta lentiviral tagging system is an innovative way to track ITH and clonal evolution in glioblastoma orthotopic models. We hope to discover novel insights into TMZ treatment response and resistance. Citation Format: Jennifer Brooke Goldstein, Ravesanker Ezhilarasan, Mona Jaffari, Alessandro Carugo, Giulio Draetta, Roeland Verhaak, Sahil Seth, Erik Sulman, Phillip Andrew Futreal. The clonal evolution of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2916. doi:10.1158/1538-7445.AM2017-2916

Mismatch repair deficiency commonly precedes adenoma formation in Lynch Syndrome-Associated colorectal tumorigenesis.

Lynch syndrome is a cancer predisposition syndrome caused by germline mutations in mismatch repair (MMR) genes. MMR deficiency is a ubiquitous feature of Lynch syndrome-associated colorectal adenocarcinomas; however, it remains unclear when the MMR-deficient phenotype is acquired during tumorigenesis. To probe this issue, the present study examined genetic alterations and MMR statuses in Lynch syndrome-associated colorectal adenomas and adenocarcinomas, in comparison with sporadic adenomas. Among the Lynch syndrome-associated colorectal tumors, 68 of 86 adenomas (79%) and all adenocarcinomas were MMR-deficient, whereas all the sporadic adenomas were MMR-proficient, as determined by microsatellite instability testing and immunohistochemistry for MMR proteins. Sequencing analyses identified APC or CTNNB1 mutations in the majority of sporadic adenomas (58/84, 69%) and MMR-proficient Lynch syndrome-associated adenomas (13/18, 72%). However, MMR-deficient Lynch syndrome-associated adenomas had less APC or CTNNB1 mutations (25/68, 37%) and frequent frameshift RNF43 mutations involving mononucleotide repeats (45/68, 66%). Furthermore, frameshift mutations affecting repeat sequences constituted 14 of 26 APC mutations (54%) in MMR-deficient adenomas whereas these frameshift mutations were rare in MMR-proficient adenomas in patients with Lynch syndrome (1/12, 8%) and in sporadic adenomas (3/52, 6%). Lynch syndrome-associated adenocarcinomas exhibited mutation profiles similar to those of MMR-deficient adenomas. Considering that WNT pathway activation sufficiently drives colorectal adenoma formation, the distinct mutation profiles of WNT pathway genes in Lynch syndrome-associated adenomas suggest that MMR deficiency commonly precedes adenoma formation.

Mismatch repair (MMR) detection in urothelial carcinoma (UC) and correlation with immune checkpoint blockade (ICB) response.

4511 Background: High mutation burden correlates with response to ICB in UC. Loss of function alterations or epigenetic silencing of MMR genes results in MMR deficient (MMR-D) UC, leading to a microsatellite instability (MSI) mutation signature. We used a CLIA-certified pipeline (MSISensor) to interrogate Next Generation sequencing (NGS) data from UC tumors to identify MMR-D patients (pts). We correlated MMR-D with mutation load and response to ICB. Methods: 447 tumors from 424 UC pts underwent prospective NGS using the MSK-IMPACT exon capture assay and genomic interrogation of microsatellite (MS) sites using MSIsensor, which assesses the number/length of MS within the targeted regions of tumor-normal sample pairs. Loci are considered unstable (somatic) if k-mer distributions are significantly different between tumor and matched normal using a standard multiple testing correction of χ2 p-values. The fraction of unstable sites is reported as an MSIsensor score. MSI high tumors have scores >10 while <3 are denoted MS stable. Scores from 3-10 were categorized as MS intermediate. Results: Thirteen pts (3%) had an MSI score >10 and a median mutation count of 52 (36.5-73.5) vs 8 (5-13) in 410 non-MMR-D pts (p<0.01). Ten pts (71%) had upper tract UC. Of 9 pts with germline sequencing performed, 8 (89%) had heritable loss of function mutations in MMR proteins (Lynch syndrome, LS). One pt had a somatic MSH2 mutation. Fifteen pts had MS scores from 3-10: 3 had LS, one a BRCA1 germline alteration, and 9 did not have germline testing available. Two pts with MSI scores <3 had extremely high mutation loads (213 and 414) and both had POLE mutations. Five pts received ICB therapy for metastatic and all achieved near-complete or complete responses. No MMR-D pt has died at 27 months follow-up vs 125 non-MMR-D pts (p=0.014). Conclusions: The MSI Sensor assay can discriminate MSI high from MMR proficient UC. While rare, MMR-D UC is characterized by a high mutation load, strong association with Lynch syndrome, and durable responses to ICB, similar to data in colon cancer. An MMR-D signature should trigger genetic testing for Lynch syndrome. ICB should be considered early in the treatment course of patients with MMR-D metastatic UC.

Intratumoral heterogeneity of intrahepatic cholangiocarcinoma.

335 Background: No personalized therapy regimens could demonstrate a benefit in survival in intrahepatic cholangiocarcinoma (iCCA). Since genetic heterogeneity might influence single biopsy based targeted therapy or the outcome of clinical trials, aim of the present study was to investigate intratumoral heterogeneity of iCCA by whole exome sequencing. Methods: Samples from tumor center and tumor periphery of large iCCA lesions as well as a control from healthy liver tissue were obtained from 4 patients and whole exome sequencing was performed. Mutations that occurred only in the tumor center or periphery were defined as private, whereas mutations present in both samples were regarded as common. Results: A mean of 3 non-synonymous private mutations (range 0-13) per sample compared to 31.8 common mutations per sample (range 23-39) was identified. Mean percentage of non-synonymous private mutations per sample was 12% (range 0-57). In all samples of patient 1-3 as well as the central sample of patient 4 ≤ 10% private mutations were found, whereas 57% of private mutations were identified in the peripheral sample of patient 4. In this sample, a private mutation in the DNA mismatch repair protein MSH6 as well as a spatial loss of expression of MSH6 could be identified most likely causing the high amount of private mutations. No substantial intratumoral heterogeneity was found in copy number variation analysis apart from a heterozygous duplication of chromosome 6p of patient 4. Conclusions: iCCA show a small but distinct intratumoral heterogeneity. Somatic mutations in mismatch repair proteins might contribute significantly to increased spatial tumor burden and thereby can have crucial impact on clinical management.

Simplified microsatellite instability detection protocol provides equivalent sensitivity to robust detection strategies in Lynch syndrome patients.

Objective: Germline mutations in mismatch repair (MMR) genes cause Lynch syndrome (LS). LS is an inherited disease, and an important consequence of MMR deficiency is microsatellite instability (MSI) phenotype. MSI phenotype influences the efficacy of 5 fluorouracil (5-FU) chemotherapy. Reproducible, cost effective, and easy to perform laboratory tests are required to include MSI detection in routine laboratory practice. Evaluation of CAT25 as monomorphic short tandem repeat sequence enables CAT25 to be an efficient screening tool among hereditary nonpolyposis colorectal cancer (HNPCC) patients compared with other methods used currently.Methods: Based on Amsterdam II criteria, 31 patients in 31 families were shortlisted from a total number of 1,659 colorectal cancer patients. MSI status was examined in these patients using CAT25 and a commercially available Promega MSI five-marker-based detection system as well as immunohistochemical (IHC) staining of four important MMR proteins. Patients were scored as high microsatellite instable (MSI-H), low (MSI-L), or stable (MSS). MSI status determined by CAT25 single mononucleotide marker was compared with that of five mononucleotide markers, Promega commercial kit, and IHC method.Results: MMR protein deficiency was observed on 7/31 probands using IHC methodology and 6/31 categorized as MSI-H using commercial kit or CAT25 single marker. The sensitivity and specificity of the CAT25 single marker were the same as those detected by five-marker Promega commercial kit in our patients.Conclusions: Based on our results, the performance of the CAT25 single mononucleotide marker for MSI status determination in our HNPCC patients is the same as that of the five-marker-based commercial kit.

Analysis of Lynch Syndrome Mismatch Repair Genes in Women with Endometrial Cancer

Objective: Endometrial cancer is the second most frequent neoplasm in women with Lynch syndrome (LS). We sought to assess whether analyzing women with endometrial cancer would identify families with LS not identified with current clinical criteria. Methods: We included women diagnosed with endometrial cancer younger than 50 years and also older if they had a family cancer history associated with LS. In blood samples obtained, we analyzed mutations in mismatch repair (MMR) genes, as well as protein expression by immunohistochemistry and microsatellite instability (MSI) in tumour tissue. Results: A total of 103 patients were enrolled. We detected 14 pathogenic mutations and 4 genetic variants of unknown clinical significance in MMR genes. We found MSI in 41.66% of the women with a pathogenic mutation. In this group, 76.92% showed loss of at least one MMR protein. Women with mutations were younger at diagnosis, but all of them had a family history compatible with LS. Conclusions: Analysis of the MMR genes, in particular MSH6, seems to be appropriate in women with endometrial cancer and a family history of tumours associated with LS.

Frequent PIK3CA Mutations in Colorectal and Endometrial Tumors With 2 or More Somatic Mutations in Mismatch Repair Genes

Some colorectal and endometrial tumors with microsatellite instability not attributable to MLH1 hypermethylation or germline mutations contain 2 or more somatic mutations in genes encoding mismatch repair (MMR) proteins. We sought to define the molecular phenotype of this newly recognized tumor subtype. From 2 prospective studies of the efficacy of screening for Lynch syndrome, we identified patients with colorectal and endometrial tumors who had 2 or more somatic (but not germline) mutations in genes encoding MMR proteins (double somatic). We determined the frequencies of tumor mutations in PIK3CA, BRAF, KRAS, NRAS, and PTEN by targeted next-generation sequencing and used logistic-regression models to compare them with those from patients with Lynch syndrome, MLH1-hypermethylated, or microsatellite-stable tumors. We validated our findings using independent data sets from The Cancer Genome Atlas. Among colorectal cancer cases, we found that 14 of 21 (67%) patients with double somatic tumors also had PIK3CA mutations, compared with 4 of 18 (22%) tumors from patients with Lynch syndrome, 2 of 10 (20%) tumors with MLH1 hypermethylation, and 12 of 78 (15%) tumors with microsatellite stability (P < .0001 for patients with double somatic tumors vs other subgroups). Mutations in PIK3CA were detected in all 13 patients with double somatic endometrial cancers (P= .04 compared with other subgroups). We did not detect BRAF mutations in patients with double somatic colorectal tumors or Lynch syndrome. We found highly similar results in a validation cohort from The Cancer Genome Atlas (113 patients with colorectal tumors, 178 endometrial tumors); 100% of double somatic cases had a somatic mutation inPIK3CA (P < .0001 compared with other subgroups). Most patients with colorectal or endometrial tumors with 2 or more somatic (but not germline) mutations in MMR proteins also have mutations in PIK3CA; mutations in PIK3CA are detected at substantially higher frequencies in these double somatic tumors than in other microsatellite-instability subgroups. PIK3CA mutation status might be used to identify a specific group of colorectal tumors, and to select treatment or determine prognosis.

Prognostic impact of mismatch repair genes germline defects in colorectal cancer patients: are all mutations equal?

Lynch syndrome (LS) is the most common hereditary colorectal cancer (CRC) syndrome, caused by germline mutations in MisMatch Repair (MMR) genes, particularly in MLH1, MSH2 and MSH6. Patients with LS seem to have a more favourable prognosis than those with sporadic CRC, although the prognostic impact of different mutation types is unknown. Aim of our study is to compare survival outcomes of different types of MMR mutations in patients with LS-related CRC. 302 CRC patients were prospectively selected on the basis of Amsterdam or Revised Bethesda criteria to undergo genetic testing: direct sequencing of DNA and MLPA were used to examine the entire MLH1, MSH2 and MSH6 coding sequence. Patients were classified as mutation-positive or negative according to the genetic testing result. A deleterious MMR mutation was found in 38/302 patients. Median overall survival (OS) was significantly higher in mutation-positive vs mutation-negative patients (102.6 vs 77.7 months, HR:0.63, 95%CI:0.46-0.89, p = 0.0083). Different types of mutation were significantly related with OS: missense or splicing-site mutations were associated with better OS compared with rearrangement, frameshift or non-sense mutations (132.5 vs 82.5 months, HR:0.46, 95%CI:0.16-0.82, p = 0.0153). Our study confirms improved OS for LS-patients compared with mutation-negative CRC patients. In addition, not all mutations could be considered equal: the better prognosis in CRC patients with MMR pathogenic missense or splicing site mutation could be due to different functional activity of the encoded MMR protein. This matter should be investigated by use of functional assays in the future.

Detailed characterization of MLH1 p.D41H and p.N710D variants coexisting in a Lynch syndrome family with conserved MLH1 expression tumors.

Lynch syndrome (LS) is an autosomal dominant cancer-susceptibility disease caused by inactivating germline mutations in mismatch repair (MMR) genes. Variants of unknown significance (VUS) are often detected in mutational analysis of MMR genes. Here we describe a large family fulfilling Amsterdam I criteria carrying two rare VUS in the MLH1 gene: c.121G > C (p.D41H) and c.2128A > G (p.N710D). Collection of clinico-pathological data, multifactorial analysis, in silico predictions, and functional analyses were used to elucidate the clinical significance of the identified MLH1 VUS. Only the c.121G > C variant cosegregated with LS-associated tumors in the family. Diagnosed colorectal tumors were microsatellite unstable although immunohistochemical staining revealed no loss of MMR proteins expression. Multifactorial likelihood analysis classified c.2128A > G as a non-pathogenic variant and c.121G > C as pathogenic. In vitro functional tests revealed impaired MMR activity and diminished expression of c.121G > C. Accordingly, the N710 residue is located in the unconserved MLH1 C-terminal domain, whereas D41 is highly conserved and located in the ATPase domain. The obtained results will enable adequate genetic counseling of c.121G > C and c.2128A > G variant carriers and their families. Furthermore, they exemplify how cumulative data and comprehensive analyses are mandatory to refine the classification of MMR variants.

Immunohistochemistry for Annexin A10 Can Distinguish Sporadic From Lynch Syndrome–associated Microsatellite-unstable Colorectal Carcinoma

Differentiating sporadic microsatellite-unstable colorectal carcinoma due to MLH1 promoter hypermethylation from Lynch syndrome (LS)-associated tumors due to mutations in mismatch-repair proteins is time consuming, cost intensive, and requires advanced laboratory testing. A mutation in BRAF has been shown to be highly specific for sporadic tumors; however, a significant proportion of sporadic microsatellite-unstable tumors lack BRAF mutations. MLH1 promoter methylation analysis is subsequently used to differentiate LS and sporadic tumors, but both tests require specialized laboratories and are costly. Through previous gene expression profiling of serrated polyps, we identified annexin A10 as a protein highly expressed in sessile serrated adenomas/polyps. As these polyps give rise to the majority of sporadic microsatellite-unstable tumors, we evaluated the ability of annexin A10 expression to discriminate between LS and sporadic tumors. A marked increase in annexin A10 mRNA was observed in sporadic microsatellite-unstable tumors compared with LS tumors (378-fold increase, P<0.001). Using immunohistochemistry, annexin A10 was expressed in 23/53 (43%) BRAF-mutated and 9/22 (41%) BRAF wild-type sporadic tumors. In contrast, only 3/56 (5%) LS tumors were positive for annexin A10 (P<0.0001). One patient had a deleterious MSH2 mutation, and another had a variant of uncertain significance in MSH6. These 2 tumors could be easily distinguished from sporadic tumors using mismatch-repair protein immunohistochemistry. Only 1/28 (4%) LS tumors with loss of MLH1 was positive for annexin A10. This patient did not have a deleterious MLH1 mutation but rather germline promoter hypermethylation of MLH1. On the basis of these results, immunohistochemistry for annexin A10 may be a useful marker to distinguish sporadic from LS-associated microsatellite-unstable colon cancer.

Identifying Lynch Syndrome in Patients With Ovarian Carcinoma

Up to 15% of ovarian cancers are etiologically linked with hereditary susceptibility. Within this group, germline mutations in mismatch repair (MMR) genes, known otherwise as Lynch syndrome (LS), account for the majority of cases that are not associated with mutations in BRCA1 or BRCA2. Clinical schemas specific for gynecologic cancers have been developed to identify patients with LS; however, many of the recommendations are poorly defined. Few case series of germline-confirmed LS-associated ovarian cancers have been reported, limited by small sample size and often lacking central pathology review. Much insight has been gained from studies of unselected cohorts, using immunohistochemical assessment of MMR protein expression or microsatellite instability analysis. In spite of contradictory results, likely reflective of differences in study design, sample size and methodology, a recurring observation is the overrepresentation of "endometriosis-associated tumors," namely, endometrioid and clear cell subtypes, in the group of ovarian tumors with MMR deficiency. In this review, we summarize the clinical and histomorphologic features of LS-associated/MMR-deficient ovarian epithelial cancers and recommend that reflex testing be performed on the basis of tumor subtype.

Patients with Lynch Syndrome Mismatch Repair Gene Mutations Are at Higher Risk for Not Only Upper Tract Urothelial Cancer but Also Bladder Cancer

BackgroundLynch syndrome (LS), or hereditary nonpolyposis colorectal cancer, is caused by mutations in mismatch repair (MMR) genes. An increased risk for upper tract urothelial carcinoma (UTUC) has been described in this population; however, data regarding the risk for bladder cancer (BCa) are sparse. ObjectiveTo assess the risk of BCa in MMR mutation carriers and suggest screening and management recommendations. Design, setting, and participantsCancer data from 1980 to 2007 were obtained from the Familial Gastrointestinal Cancer Registry in Toronto for 321 persons with known MMR mutations: mutL homolog 1, colon cancer, nonpolyposis type 2 (E. coli) (MLH1); mutS homolog 2, colon cancer, nonpolyposis type 1 (E. coli) (MSH2); mutS homolog 6 (E. coli) (MSH6); and PMS2 postmeiotic segregation increased 2 (S. cerevisiae) (PMS2). Outcome measurements and statistical analysisStandardized incidence ratios from the Ontario Cancer Registry, using the Surveillance Epidemiology and End Results public database, were used to compare cancer risk in patients with MMR mutations with the Canadian population. Microsatellite instability analysis and immunohistochemistry (IHC) of the MMR proteins were also performed and the results compared with matched sporadic bladder tumors. Results and limitationsEleven of 177 patients with MSH2 mutations (6.21%, p<0.001 compared with the Canadian population) were found to have BCa, compared with 3 of 129 patients with MLH1 mutations (2.32%, p>0.05). Of these 11 tumors, 81.8% lacked expression of MSH2 on IHC, compared with the matched sporadic cases, which all displayed normal expression of MSH2 and MLH1. The incidence of UTUC among MSH2 carriers was 3.95% (p<0.001), and all tumors were found to be deficient in MSH2 expression on IHC. Mutations in the intron 5 splice site and exon 7 of the MSH2 gene increased the risk of urothelial cancer. Limitations include possible inflated risk estimates due to ascertainment bias. ConclusionsLS patients with MSH2 mutations are at an increased risk for not only UTUC but also BCa and could be offered appropriate screening.