PMS2 Mutations Research Articles

Investigation of Hereditary Cancer Predisposition Genes of Patients with Colorectal Cancer: Single-centre Experience.

To investigate the genetic causes of colorectal cancers (CRCs); and to determine the genotype-phenotype correlation. Descriptive study. Department of Medical Genetics, Diskapi Yildirim Beyazit Training and Research, Hospital, Ankara, Turkey, between January 2018 and January 2020. 59 cancer susceptibility genes of 41 patients, included in the study and diagnosed with CRC, were examined using next generation sequencing (NGS) technique. Statistical analysis of the possible relationships among the mutation carrier status of the patients and the parameters of gender, age at diagnosis, and family cancer history, were performed. The mean age at diagnosis of all CRC patients was 48.7 years (range 28-74). Mutations in MLH1, MSH6, CHEK2, PMS2 and MUTYH genes were detected in 10 patients (24.4%). The mean age at diagnosis of CRC was 46.2 years in those who carried the mutation, while it was 49.5 years in those without. Carriers and non-mutation carriers, when compared in terms of age at diagnosis, gender, family cancer history, no significant difference was observed. Genes that may cause susceptibility to cancer may play a role in the etiopathogenesis of the CRC. NGS-based multigene panels allow these genes to be detected in the patient and to identify an inherited cancer syndrome. Key Words: Colorectal cancer, Lynch syndrome, Hereditary cancer, Gene, Next generation sequencing.

Abstract 2605: A natural history study of men with high-risk genetics for prostate cancer (PCa) using multiparametric MRI (mpMRI)

Abstract Introduction: The understanding of molecular genetics in PCa provides insight into disease progression and treatment. Less is known about PCa development in men with known high-risk germline pathogenic/likely pathogenic variants in PCa related genes, particularly DNA damage repair (DDR). mpMRI can localize and detect PCa lesions in this population. We are conducting a multicenter natural history study of male participants (prts) with documented germline variant(s) in BRCA1, BRCA2, MLH1, MSH2, MSH6, PMS2, EPCAM, HOXB13, ATM, NBN, TP53, CHEK2, PALB2, RAD51D, BRIP1, or FANCA who do not have a PCa diagnosis using mpMRI (NCT03805919). Methods: Up to 500 men, 30-75 years old (y/o) will undergo mpMRI evaluation at baseline and every 2 years (yrs). Prts are followed at 12-mo intervals to determine PSA, PCa diagnosis, and/or disease/survival status until death. Indication for prostate biopsy includes PSA >2.0 for 30 - 49 y/o; >2.5 ng/mL for 50 - 75 y/o and/or PIRADS 3+ MRI lesion or clinical discretion. Tissue obtained will undergo full transcriptome analysis. Results: 100 prts have enrolled. Median age is 47 y/o. Median on-study PSA is 0.87 (0.16-10.05 ng/mL). Median PSA density is 0.029. Gene mutations are BRCA2 (40%), BRCA1 (33%), MSH2 (9%), and CHEK2 (4%). Mutations in ATM, HOXB13, MLH1, MSH6, PMS2, and EPCAM are ≤3%. No significant AEs have been observed. Of 96 prts, 25 (26%), had indication for biopsy [PIRADS 4 lesion: 16 (64%), PIRADS 3 lesion: 4 (16%), elevated PSA: 6 (24%), or clinical indication 1: (4%)]. 22 prostate biopsies were performed and 6 prts were diagnosed with PCa. One prt was upstaged on radical prostatectomy (RP). Conclusions: We found mpMRI-based PCa screening in men with high-risk gene mutations, especially DDR genes, is feasible and can be used to identify clinically significant PCa and monitor for disease progression. Future guidelines should consider age, mutation specificity and mpMRI. Accrual and correlative studies (biomarkers, PBMCs) are on-going. AgeMutationPSA (ng/mL)Biopsy Gleason ScoreTreatment65BRCA22.253+3RP52BRCA10.693+3Active Surveillance (AS)62CHEK22.493+3AS59PMS21.033+3AS59CHEK22.243+4Radiation55BRCA21.683+3RP: 4+4=8 Citation Format: Fatima Karzai, Anna Couvillon, Yolanda McKinney, Katherine Lee-Wisdom, Peter L. Choyke, Veda N. Giri, Todd M. Morgan, Heather H. Cheng, Maria J. Merino, Peter A. Pinto, Baris Turkbey, William L. Dahut. A natural history study of men with high-risk genetics for prostate cancer (PCa) using multiparametric MRI (mpMRI) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2605.

Comprehensive Sequencing Analysis in Subcutaneous Panniculitis-like T-Cell Lymphoma

Subcutaneous panniculitis-like T-cell lymphoma (SPTL) is a rare subtype of peripheral T-cell lymphomas predominantly affecting younger individuals. Typically, SPTL presents with multifocal subcutaneous nodules, and nearly 20% of the patients have autoimmune disorders, including systemic lupus erythematosus, juvenile rheumatoid arthritis and Sjögren disease. Unlike other lymphomas, which usually require chemotherapy for long-term survival, immunosuppressive therapy alone yields favorable outcomes in SPTL. A previous study showed allelic NAV3 gene aberrations (LOH or deletion by FISH) in 44% of the SPTL samples and comparative genomic hybridization (CGH) revealed numerous DNA copy number changes. In another study, recurrent mutations were identified in various epigenetic modifiers (72%) and components of the PI3K/AKT/mTOR signaling pathway (44%). However, molecular pathogenesis of this disease has not been clearly understood.To elucidate the causative genetic lesions of SPTL, we collected 13 patients from Thailand (n=12) and Japan (n=1). Histopathology was reviewed by hematopathologists showing karyorrhexis of tumor cells infiltrating fat lobules. In all cases, lymphoma cells expressed CD3, CD5, CD8 and TIA1 but no CD56 suggesting the cytotoxic T-cells in origin. Tumor cells expressed T-cell receptor alpha/beta. The monoclonality was confirmed by southern blot (n=12). The mean percentage of SPTL cells in tissue blocks was 38% (range 20-80%). The majority of cases (75%) showed a high proliferative index (Ki-67 expression > 70%).Regarding the clinical data, 10 of 13 patients (80%) were female. The median age at diagnosis was 30 years old. Five cases (38.5%) showed systemic symptoms and 2 cases (20%) were associated with hemophagocytic syndromes. Seven cases received cyclosporine and prednisolone. All showed complete response but 2 cases relapsed. Six cases received anthracycline-based chemotherapy but 3 cases relapsed. All relapses responded to immunosuppressive therapy.We collected paired samples from each of cases (n=13). Tumor samples were collected from Formaldehyde Fixed-Paraffin Embedded (FFPE) tissues whereas germline samples were collected from either bone marrow FFPE or blood which showed no tumor involvement. We performed whole-exome and targeted-capture sequencing in those paired tumor/germline DNA samples by SureSelect v5 kit and custom kit, respectively. To identify somatic mutations and structural variations, sequencing data was analyzed using Genomon (ver. 2.3.0) and Genomon-SV. Copy number was analyzed based on sequencing data as described previously (ASH 2016 abstract by Saeki, et al.).By whole exome sequencing, 149 mutation calls were identified in 8 samples. The somatic mutations and copy number variations were grouped into 4 biological pathways which are commonly affected in cancer.1. Apoptotic associated pathway (FADD , ACIN1 , and PPM1L) : Interestingly, a nonsense mutation of FADD was found and validated. FADD protein is critical for promoting apoptosis of T-cell progenitors at the pre-TCR checkpoint.2. Epigenetic modifier pathway (GFIB , SAB130 and CHD9) : Notably, GFI1B mutation was found to be frameshift deletion causing protein truncation. Gfi1b repressed the Gata3, a transcription factor required for survival of T-lymphocyte progenitors.3. Translation initiation pathway (DHX29 and CTIF) : Missense mutation of DHX29 was identified whereas copy number analysis revealed one case possessed focal amplification of CTIF , a component of the CBP80/CBP20 translation initiation complex and associated with nonsense-mediated decay of mRNA.4. Transcription factors (MEF2B and MGA ): Targeted sequence detected mutations in MEF2B, MGA and PMS2 , which are associated with regulation of BCL6, MYC-MAX pathway and DNA mismatch repair, respectively.At least one mutation involved in either of such 4 pathways was identified in 5/8cases (62.5%). In addition, Sequence based T-cell receptor repertoire analysis proved monoclonal expansion in 5 cases.In conclusion, the identifications of novel genetic alterations provide an insight into the lymphomagenesis of SPTL. Heterogeneous mutations in different candidate pathways suggest complexpathogenesis of this rare tumor. DisclosuresMakishima:Yasuda Medical Foundation: Research Funding.

Family history of early onset acute lymphoblastic leukemia is suggesting genetic associations

Childhood acute lymphoblastic leukemia (ALL) has an origin in the fetal period which may distinguish it from ALL diagnosed later in life. We wanted to test whether familial risks differ in ALL diagnosed in the very early childhood from ALL diagnosed later. The Swedish nation-wide family-cancer data were used until year 2016 to calculate standardized incidence ratios (SIRs) for familial risks in ALL in three diagnostic age-groups: 0–4, 5–34 and 35 + years. Among 1335 ALL patients diagnosed before age 5, familial risks were increased for esophageal (4.78), breast (1.42), prostate (1.40) and connective tissue (2.97) cancers and leukemia (2.51, ALL 7.81). In age-group 5–34 years, rectal (1.73) and endometrial (2.40) cancer, myeloma (2.25) and leukemia (2.00, ALL 4.60) reached statistical significance. In the oldest age-group, the only association was with Hodgkin lymphoma (3.42). Diagnostic ages of family members of ALL patients were significantly lower compared to these cancers in the population for breast, prostate and rectal cancers. The patterns of increased familial cancers suggest that BRCA2 mutations could contribute to associations of ALL with breast and prostate cancers, and mismatch gene PMS2 mutations with rectal and endometrial cancers. Future DNA sequencing data will be a test for these familial predictions.

Long-read nanopore sequencing enables accurate confirmation of a recurrent PMS2 insertion–deletion variant located in a region of complex genomic architecture

Targeted next generation sequencing (NGS) is the predominant methodology for the molecular genetic diagnosis of inherited conditions. In many laboratories, NGS-identified variants are routinely validated using a different method, to minimize the risk of a false-positive diagnosis. This can be particularly important when pathogenic variants are located in complex genomic regions. In this situation, new long-read sequencing technologies have potential advantages over existing alternatives. However, practical examples of their utility for diagnostic purposes remain scant. Here, we report the use of nanopore sequencing to validate a PMS2 mutation refractory to conventional methods. In a patient who presented with colorectal cancer and loss of PMS2 immunostaining, short-read NGS of Lynch syndrome-associated genes identified the recurrent PMS2 insertion-deletion variant, c.736_741delinsTGTGTGTGAAG (p.Pro246Cysfs*3). Confirmation of this variant using bidirectional Sanger sequencing was impeded by an upstream intron 6 poly(T) tract. Using a locus-specific amplicon template, we undertook nanopore long-read sequencing in order to assess the diagnostic accuracy of this platform. Pairwise comparison between a curated benchmark allele (derived from short-read NGS and unidirectional Sanger sequencing) and the consensus nanopore dataset revealed 100% sequence identity. Our experience provides insight into the robustness and ease of deployment of “third-generation” sequencing for accurate characterisation of pathogenic variants.

Lynch Syndrome in Thai Endometrial Cancer Patients.

Background:Lynch syndrome increases lifetime risk of endometrial cancer to 40-60%. Screening with molecular tumor testing for mismatch repair (MMR) proteins have been recommended. This study aims to evaluate the incidence of MMR deficiency and germline mutation in endometrial cancer Thai patients. Methods:Immunohistochemistry for MMR proteins, including MLH1, MSH2, MSH6 and PMS2 were tested in 166 surgical specimens. Patients who had MMR deficiencies were offered genetic counseling and a germline testing using gene-panel next generation sequencing. Results:Fifty-eight of 166 patients (34.9%) had one or more MMR deficiencies which were: MLH1 and PMS2 in 42 patients (25.3%), MSH2 and MSH6 in 11 patients (6.6%), and MSH6 in 5 patients (3.0%). Of the 40 patients (24.1%) who met the revised Bethesda guidelines, 19 patients (47.5%) had MMR deficiency. In contrast, MMR deficiency was found in 39 of the 126 patients (31.0%) who did not meet the revised Bethesda guidelines. A total of 27 patients with MMR deficiencies agreed to have germline genetic testing. Germline MMR mutations were detected in 5 patients (18.5%) including MSH6 (n=2), PMS2 (n=2), and MLH1 mutations (n=1). Incidental germline mutations in other genes were detected in 3 patients (1 BRCA1, 1 PTEN, and 1 BARD1). Among 5 Lynch syndrome patients, 2 patients (40%) did not meet the revised Bethesda guidelines. Eight patients who met the revised Bethesda Guidelines but having MMR proficiency had genetic testing, but no germline mutation was detected. Conclusion:MMR deficiencies were detected in 34.9% of the endometrial cancer patients. Germline mutations were diagnosed in 3.0% of this cohort (5/166 patients). Lynch syndrome screening with MMR immunohistochemistry should be considered in all patients regardless of personal or family history of Lynch syndrome-related cancers.

The clinical and molecular characteristics of patients with personal history of colorectal cancer evaluated by cancer genetics counseling services.

46 Background: Genetic susceptibility to colorectal cancer (CRC) include well-defined hereditary syndromes such as Lynch Syndrome, Familial Adenomatous Polyposis syndrome (FAP), MUTYH-Associated Polyposis syndrome (MAP) and other less common syndromes. National Comprehensive Cancer Network (NCCN) guidelines recommend that individuals meeting certain criteria have detailed risk assessment and potential genetic testing. Here, we describe the clinical and molecular characteristics of patients with personal history of CRC evaluated by cancer genetics counseling services. Methods: This is an IRB-approved retrospective chart-review study. Between 2016 and 2020, 1011 unique genetic counseling visits were conducted. Germline testing was recommended by a certified genetic counselor if medically necessary. All patients with a personal history of CRC were identified (N = 52) and their clinical and molecular characteristics were summarized. Results: The median age is 50 years-old (29-82). Thirty-five (67%) patients were females. Caucasians, African Americans and other ethnic backgrounds represented 75%, 19% and 6% respectively. The primary tumor location was in the right colon, left colon and rectum in 29%, 37% and 27% of our cohort respectively. In 7%, the primary location of the tumor was not available. In our cohort, 11 out of 52 (21%) patients had a pathogenic germline mutation and 9 patients (17%) had a germline variant of unknown significance (VUS). Among patients with pathogenic germline mutations (N = 11), 4 patients had MSH2 mutations (MSH2 c.1759+1G > A, MSH2 c. 1687dupT, MSH2 c.1861C > T and MSH2 c.811_814delTCTG), 1 patient had a MSH6 mutation (MSH6 c.1012A > T), 1 patient had a PMS2 mutation (PMS2 c.2182_2184delACTinsG), 3 patients had CHEK2 mutations (CHEK2 c.1100delC and CHEK2 c.470T > C (p.I157T)), 2 patients had MUTYH mutations (MUTYH c.1187G > A and MUTYH c.536A > G) and 1 patient had a BRCA2 mutation (BRCA2 c.2808_2811delACAA). One patient had a CHEK2 and a MUTYH mutation. The VUS mutations in our cohort were POLE c.1645T > C, POLE c.5480C > T, c.2999G > A, MLH1 c.1628A > G, CTNNA1 c.503G > A, MSH2 c.128A > G, NBN c.16C > T, ATM c.6537T > G and AXIN2, BRCA1, NTHL1 mutations. Conclusions: In our cohort of patients with personal history of CRC, the majority of patients (62%) had negative germline testing. An underlying pathogenic germline mutation and VUS were identified in 21% and 17% of the patients respectively. Lynch Syndrome was the most commonly diagnosed hereditary CRC syndrome with 6 out of 11 patients found to have MMR germline mutations. Other pathogenic mutations were identified in the CHEK2, MUTYH and BRCA2 genes.

The importance of MLH1, MSH2, MSH6 and PMS2 in determining DNA damage response in digestive cancers

Introduction: Genomic instability is a common feature across human cancers, but presents variation across different types of cancer, patients and cells of from the same tumor.This can be caused either by changes in the DNA damage repair pathways, aberrant histone modifications or methylation. The aim of this study was to determine the common mutated genes between digestive cancers that present genomic instability and to determine the biological processes in which these are implicated. Material and Methods: Mutational profiles for patients presenting digestive cancers and mutations in MLH1, MSH2, MSH6 and PMS2 were downloaded from the MSK impact cohort via cBioPortal. PANTHER was used to determine the GO SLIM processes in which the mutated genes are involved. R 3.5.3 and the R package circlize were used to generate chord diagrams. Results and Discussions: Considering the number of mutated genes from different digestive cancers it could be observed that the deregulated processes are general cellular processes, while when taking into consideration the fold change in overrepresentation of certain processes, the main deregulated processes are represented by DNA damage repair pathways, showing their overrepresentation in the selected cohort based on a few mutated genes. Conclusion: MLH1,MSH2,MSH6 and PMS2 mutations dictate the alterations in DNA damage repair pathways in digestive cancers.

NFB-06. TREATMENT CHALLENGES IN PEDIATRIC GLIOBLASTOMA MULTIFORME WITH CONCURRENT SOMATIC AND GERMLINE NF1 MUTATIONS WITH GERMLINE MISMATCH REPAIR MUTATIONS: TWO UNIQUE CASES

INTRODUCTIONWe report the first known cases of pediatric glioblastoma (GBM) with prior clinical NF1 diagnoses, one with concurrent germline Lynch syndrome (LS) and NF1, and the other with somatic NF1 mutation and germline constitutional mismatch repair deficiency (CMMRD).METHODSTwo pediatric GBM cases with prior NF1 clinical diagnoses based on neurocutaneous criteria were reviewed. Next generation sequencing and immunohistochemical staining were used for somatic and germline NF1 and MMR gene mutation detection, and for MMR protein expression, respectively.RESULTSSixteen year old male with prior NF1 clinical diagnosis had resection of right frontal GBM revealing somatic mutations of POLE and PMS2, but not NF1. His father had confirmed LS with MSH2 mutation and no neurocutaneous stigmata. Patient’s germline testing revealed both pathogenic MSH2 plus NF1 mutations confirming LS and NF1. Treatment consisted of chemoradiation with temozolomide followed by adjuvant temozolomide with stable disease at 8 cycles. Nineteen year old male with former NF1 clinical diagnosis had 2 GBMs, first in left midbrain biopsied revealing somatic PMS2 and NF1 mutations underwent radiation then 7 cycles of temozolomide, then new left frontal GBM underwent resection followed by radiation and 5 cycles of pembrolizumab stable at 5th cycle.CONCLUSIONChildren with NF1 stigmata and GBM can have concurrent NF1 and LS, or CMMRD with NF1 somatic mutations. Our patients tolerated alkylating agents, despite risk for secondary malignancies as upfront therapy and at recurrence checkpoint inhibitors. Upfront therapy in GBM with mismatch repair syndrome with checkpoint inhibitors should be studied.

Cancer Previvors in an Active Duty Service Women Population: An Opportunity for Prevention and Increased Force Readiness.

BackgroundThe majority of active duty service women (ADS) are young, have access to healthcare, and meet fitness standards set by the U.S. military, suggesting that ADS represent a healthy population at low risk of cancer. Breast cancer is, however, the most common cancer in ADS and may have a significant effect on troop readiness with lengthy absence during treatment and inability to return to duty after the treatment. The identification of unaffected ADS who carry germline mutations in cancer predisposition genes (“previvors”) would provide the opportunity to prevent or detect cancer at an early stage, thus minimizing effects on troop readiness. In this study, we determined (1) how many high-risk ADS without cancer pursued genetic testing, (2) how many previvors employed risk-reducing strategies, and (3) the number of undiagnosed previvors within an ADS population.MethodsThe Clinical Breast Care Project (protocol WRNMMC IRB #20704) database of the Murtha Cancer Center/Walter Reed National Military Medical Center was queried to identify all ADS with no current or previous history of cancer. Classification as high genetic risk was calculated using National Comprehensive Cancer Network 2019 guidelines for genetic testing for breast, ovary, colon, and gastric cancer. The history of clinical genetic testing and risk-reducing strategies was extracted from the database. Genomic DNA from ADS with blood specimens available for research purposes were subjected to next-generation sequencing technologies using a cancer predisposition gene panel.ResultsOf the 336 cancer-free ADS enrolled in the Clinical Breast Care Project, 77 had a family history that met National Comprehensive Cancer Network criteria for genetic testing for BRCA1/2 and 2 had a family history of colon cancer meeting the criteria for genetic testing for Lynch syndrome. Of the 28 (35%) high-risk women who underwent clinical genetic testing, 11 had pathogenic mutations in the breast cancer genes BRCA1 (n = 5), BRCA2 (n = 5), or CHEK2 (n = 1). Five of the six ADS who had a relative with a known pathogenic mutation were carriers of the tested mutation. All of the women who had pathogenic mutations detected through clinical genetic testing underwent prophylactic double mastectomy, and three also had risk-reducing salpingo-oophorectomy. Two (6%) of the 33 high-risk ADS tested only in the research setting had a family history of breast/ovarian cancer and carried pathogenic mutations: one carried a BRCA2 mutation, whereas the other carried a mutation in the colon cancer predisposition gene PMS2. No mutations were detected in the 177 low-risk women tested in the research setting.DiscussionWithin this unaffected cohort of ADS, 23% were classified as high risk. Although all of the previvors engaged in risk-reduction strategies, only one-third of the high-risk women sought genetic testing. These data suggest that detailed family histories of cancer should be collected in ADS and genetic testing should be encouraged in those at high risk. The identification of previvors and concomitant use of risk-reduction strategies may improve health in the ADS and optimize military readiness by decreasing cancer incidence.

NCMP-17. MISMATCH REPAIR MUTATIONS AND THE CENTRAL NERVOUS SYSTEM: A CASE SERIES OF GERMLINE MUTATIONS AND CNS MALIGNANCY

Abstract Our understanding of genetic predispositions for malignancy is continually evolving. One family of germline mutations well described in the literature is that of the DNA mismatch repair mechanism (MMR). Lynch syndrome (LS) is due to a loss of function mutation of several MMR genes- MSH2, MLH1, MSH6, and PMS2. Germline MMR mutations lead to microsatellite instability and loss of genomic integrity resulting in an increased risk for various cancers (colorectal, genitourinary, etc). LS may be as common as 1 in 400 people and some MMR mutations have been associated with gliomas. There is a paucity of information regarding frequency of glioma subtypes as well as tumor genetic and molecular characteristics which have important clinical implications. We describe a case series of 6 individuals with germline MMR mutations and brain tumors. Those with MSH2 and PMS2 mutations (n=3) developed glioblastomas at a mean age at diagnosis of 48 years. These tumors expressed MGMT hyper-methylation and high tumor mutational burden. Only one had IDH-1 mutation. Those with MLH1 mutations (n=3), did not develop gliomas. This raises the question of differential glioma subtype development based on MMR gene. It also highlights the possibility of Lynch-associated gliomas having more favorable treatment response due to MGMT methylation and potential response to immunotherapy based on high tumor mutational burden. Though the sample size is small, there appears to be a preponderance of women compared to men (5:1 respectively). Larger studies are needed to verify CNS involvement in germline MMR mutations. In doing so, we hope to identify factors that may influence clinical management and lead to a better understanding of treatment response and disease prognosis.

S1655 Dealing With the Inevitable: A Case of Lynch Syndrome Not Meeting the Amsterdam Criteria

INTRODUCTION: Lynch syndrome is one of the most common causes of hereditary colorectal cancer. The disease is mainly acquired by autosomal dominant inheritance and it has been found that 35% of patients diagnosed with colorectal cancer (CRC) have family history of neoplasia. The syndrome also places the patient at risk for extracolonic cancers including endometrial, brain, pancreas, stomach, among others. The most common cause of lynch syndrome is germline mutations of DNA mismatch repair genes. We present a case of Lynch syndrome in which the Amsterdam and Bethesda criteria were not met, however due to high suspicion, the disease was confirmed by genetic testing. CASE DESCRIPTION/METHODS: 33 years old Hispanic male that presented to our institution with 2 week history mild abdominal pain accompanied by weight loss. Computed tomography imaging was remarkable for concentric wall thickening of the transverse colon. Colonoscopy was performed and revealed a large mass in mid transverse colon occluding more than 90% of lumen which precluded further advance of scope. Pathology report of transverse colon biopsy revealed mucinous adenocarcinoma. Immunohistochemistry testing for mismatch repair proteins showed expression of MLH-1, MSH-2 and MSH6 and loss of nuclear expression of PMS2 which represented high probability of Lynch syndrome. The patient denied family history of colorectal cancer or any other Lynch syndrome related cancers. The patient underwent partial colectomy with resection of the adenocarcinoma. DISCUSSION: At the moment, there are no screening guidelines to detect Lynch-syndrome related cancers when Amsterdam criteria are not met. Once Lynch syndrome is diagnosed, screening is performed. It has been well documented in the literature that Lynch syndrome is frequently diagnosed when there is pertinent family history as established by Amsterdam and Bethesda criteria. Our case presents a patient with colorectal cancer with confirmed DNA mismatch repair genes consistent with Lynch syndrome, without family history Lynch syndrome related cancers. Mutations in PMS2 have a lower penetrance than other mutations, providing smaller increased risk of colorectal and endometrial cancer, but no increased risk of other Lynch syndrome related cancers. Mentioned findings can contribute to increase the awareness of this disease given the fact that 7% of individuals present with more than one related cancer at the time of diagnosis. By this means decreasing disease related complications and improving outcomes.

Germline biallelic Mcm8 variants are associated with early-onset Lynch-like syndrome.

Lynch syndrome is the most common cause of hereditary colorectal cancer (CRC), and it is characterized by DNA mismatch repair (MMR) deficiency. The term Lynch-like syndrome (LLS) is used for patients with MMR-deficient tumors and neither germline mutation in MLH1, MSH2, MSH6, PMS2, or EPCAM nor MLH1 somatic methylation. Biallelic somatic inactivation or cryptic germline MMR variants undetected during genetic testing have been proposed to be involved. Sixteen patients with early-onset LLS CRC were selected for germline and tumor whole-exome sequencing. Two potentially pathogenic germline MCM8 variants were detected in a male patient with LLS with fertility problems. A knockout cellular model for MCM8 was generated by CRISPR/Cas9 and detected genetic variants were produced by mutagenesis. DNA damage, microsatellite instability, and mutational signatures were monitored. DNA damage was evident for MCM8KO cells and the analyzed genetic variants. Microsatellite instability and mutational signatures in MCM8KO cells were compatible with the involvement of MCM8 in MMR. Replication in an independent familial cancer cohort detected additional carriers. Unexplained MMR-deficient CRC cases, even showing somatic biallelic MMR inactivation, may be caused by underlying germline defects in genes different than MMR genes. We suggest MCM8 as a gene involved in CRC germline predisposition with a recessive pattern of inheritance.

Pilomatricomas and café au lait macules as herald signs of constitutional mismatch repair deficiency (CMMRD) syndrome—A case report

Constitutional mismatch repair deficiency (CMMRD) syndrome results from bi-allelic mutations in DNA mismatch repair genes-MLH1, MSH2, MSH6, or PMS2. We present two siblings with CMMRD having p.Arg802Ter (c.2404C>T) homozygous mutations in PMS2 exon 14 with typical cutaneous features. This case report highlights the role of the dermatologist in early diagnosis of this condition.

Characteristics of colorectal carcinoma patients with PMS2 defects detected by immunohistochemistry.

Lynch syndrome is the most prevalent form of familial colorectal cancer (CRC) and is caused by pathogenic germline mismatch repair (MMR) gene mutations. MLH1, MSH2 and MSH6 mutations have been well studied, but the rate and characteristics of PMS2 mutations are rare, especially in China. This study enrolled 1706 unselected patients with CRC who underwent colorectal resection from June 2016 to November 2018, the MMR status and clinicopathological features were analysed. A total of 11.8% of patients with CRC had defects in at least one MMR-related protein. Among them, 8.3% were identified with PMS2 defects, and 3.1% of patients had isolated PMS2 defects. Compared with MMR-proficient CRC, PMS2-defect CRC occurred more frequently in the right colon and less frequently in the rectum, had more poorly differentiated and mucinous carcinoma cases, and had fewer perineural invasions and a lower pN stage but a more advanced pT stage and a larger tumour size. In the cases with PMS2 defect, there were fewer tumours in the right colon, fewer poorly differentiated cases and smaller tumour sizes than in the cases with both MLH1 and PMS2 defects. In addition, in cases with isolated PMS2 defects, there were more tumours in the right colon and, more mucinous carcinoma cases than in cases with MMR-proficient CRCs, but had a similar cancer onset age. This study identified the rate, clinicopathological and age characteristics of PMS2 defects in CRCs in China and highlighted the importance of universal screening and germline detection of PMS2 in CRC.

Abstract 3534: The study of Lynch syndrome in a special population reveals a strong founder effect and an unusual mutational mechanism in familial adenomatous polyposis

Abstract Lynch syndrome (LS) is the leading cause of hereditary colorectal cancer (CRC). Germline mutations in DNA mismatch-repair (MMR) genes (MLH1, PMS2, MSH2, and MSH6) are known to cause LS in the heterozygous state. Biallelic mutations in these genes cause mismatch repair cancer syndrome (MMRCS), a very rare childhood cancer syndrome that predisposes to CRC among other cancer types. In this study, we aimed to characterize the mutational landscape of LS in a large CRC cohort (n=1,207) from a population with high rates of consanguinity. The overall contribution of germline mutations in LS gene was comparable to that observed in outbred populations (26/1207). Remarkably, however, we also observed the unusual homozygous occurrence of a founder PMS2 mutation. The homozygous individual presented with massive adenomatous polyposis of the colon at age 8 years, and mutation analysis of multiple polyps revealed the occurrence of multiple independent somatic APC mutations. Our study highlights a previously unrecognized role of LS genes in triggering APC-driven tumors, a phenomenon facilitated by consanguinity. Citation Format: Abdul K. Siraj, Sandeep K. Parvathareddy, Rong Bu, Tariq Masoodi, Khadija Alobaisi, Maha Alrasheed, Saeeda O. Ahmed, Zeeshan Qadri, Padmanaban Annaiyappanaidu, Allianah Benito, Dionne R. Rala, Fowzan Al-Kuraya, Khawla S. Al-Kuraya. The study of Lynch syndrome in a special population reveals a strong founder effect and an unusual mutational mechanism in familial adenomatous polyposis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3534.

Next generation sequencing to decipher concurrent loss of PMS2 and MSH6 in colorectal cancer

BackgroundImmunohistochemistry (IHQ) is commonly used for the detection of mismatch repair proteins deficiency (MMRD). One very infrequent abnormal pattern of MMR protein expression is the loss of PMS2 and MSH6, with intact expression of MLH1 and MSH2.Case presentationWe review the frequency of this MMRD IHC pattern among 108 colorectal (CRCs) and 35 endometrial cancers in our files with loss of expression of at least one protein, and present two CRCs showing loss of PMS2 and MSH6 protein expression (1.9% of CRCs). NGS analysis of these tumours identified PMS2 mutations (R134* germline mutation in one tumour and M1R and c.1239delA somatic mutation in the other) as the primary event and somatic MSH6 mutation (c.3261dupC) as the secondary event in both tumours.ConclusionsThis study suggests that Next Generation Sequencing (NGS) tumour analysis should be considered in the algorithm of Lynch syndrome screening to detect MMR gen somatic mutation in inconclusive cases.

Analysis of germline mutations in Chinese colorectal cancer patients with next-generation sequencing.

e13651 Background: Colorectal cancer (CRC) remains one of the leading causes of morbidity and mortality around the world. Familial cancer syndromes are common in CRC, inherited syndromes including Lynch syndrome (LS), familial adenomatous polyposis (FAP), and MutY human homolog (MUTYH)-associated polyposis (MAP) were well defined. But still, there are not well-established evidence between other several genes and CRC risk. Expanded multi-gene testing may be an alternative to find out the underlying mechanism for genetic susceptibility. Our study aims to assess the germline alternation landscape of Chinese CRC patients. Methods: We performed hybrid capture-based next-generation sequencing (NGS) of 381 genes on tissues from patients with CRC between January 01, 2017 and December 02, 2019 in 3D Medicines database. Genomic alterations including single nucleotide variation (SNV), insertions/deletions, copy number variations, gene rearrangement and fusions were assessed. Results: 1360 CRC patients were included for analysis, in which 95 (7.0%) patients harbored pathogenic (80/95) and likely pathogenic (15/95) germline mutations in 28 cancer predisposition genes. 33 subjects had pathogenic variants associated with Lynch syndrome (15 mutations in MLH1, 9 mutations in MSH2, 6 mutations in MSH6, 3 mutations in PMS2, respectively). 8 subjects had pathogenic variants associated with FAP (3 APC), MAP (3 MUTYH) and Li-Fraumeni syndrome (2 TP53). In addition, 14 pathogenic mutations in moderate penetrance genes (5 ATM, 3 BLM and 6 CHEK2) were found. The frequency of pathogenic BRCA mutations were 1 alternation in BRCA1 and 3 alternations in BRCA2. Conclusions: 7.0 % of patients with Chinese CRC carried germline cancer susceptibility gene mutations. Multi-gene testing would provide references for assessing genetic susceptibility and managing increased surveillance.

MMR deficiency of lung cancer patients.

e21523 Background: DNA Mismatch repair (MMR) plays an essential role in the genetic. The main function of MMR is thought to correct post replication errors since the system could recognizes base exchanges and short DNA insertions or deletions. Somatic mutation of MMR are common detected in lung cancer, and several studies has shown that the presence of MMR mutation may be resistance to EGFR-TKI. Here we retrospectively analyzed the MMR mutation in chinese lung cancer. Methods: We retrospectively analyzed the genetic aberration in 910 Chinese lung patients. All the patients were detected by hybridization capture-based NGS 1021-gene panel. Results: Here is an interesting lung cancer case which was called EGFR T790M, TP53 and MSH2 somatic mutations without any germline mutations, and this patient showed no response to Osimertinib. We retrospectively analyzed the MMR in 910 patients and called 39 patients with MMR mutation.The percence of MLH1, MLH2, MSH3, MSH6, PMS1 and PMS2 mutations rate is as followed: 10.3% (4/39), 33.3% (13/39), 7.7% (3/39), 28.2% (11/39), 5.1% (2/39), and 15.4% (6/39) cases in PMS2 mutation. Also we found that TP53 is the most highly concurrent gene for MRR deficiency the rate is 79.5%(31/39). The rate of EGFR mutation concurrent with MMR deficiency is 27% (10/39). Conclusions: MMR deficiency was found in 4.3% chinese lung cancer and 27% of them concurrent with EGFR. [Table: see text] [Table: see text] [Table: see text]

Clinicopathologic analysis of MMR gene mutations and uterine adenocarcinomas: An updated population-based study.

e18100 Background: Endometrial carcinoma frequently harbors genetic alterations in genes encoding mismatch repair (MMR) enzymes, a finding which has important implications for adjuvant therapy. The aim of this study is to determine an optimal screening strategy to detect MMR mutations for each histologic subtype of endometrial carcinoma (EC). Methods: We performed a comparative analysis of the demographic, clinical, pathologic, and molecular data, including MLH1, MLH3, PMS1, PMS2, MSH2, MSH3, MSH6, and EPCAM, for 562 patients from The Cancer Genome Atlas database (TCGA), stratified by tumor histologic subtype. Results: Molecular data was available for 562 patients, of which 162 (28.8%) had tumors that were positive for MMR mutations. We did not separate somatic and germline mutation. Of these tumors, the penetrate rate of FIGO grade 3 endometrioid endometrial carcinoma (EEC G3) (84/184, 45.7%) was significantly higher than the one of uterine serous carcinoma (USC) (35/156, 22.4%) ( p < 0.001), grade 2 (EEC G2) (26/129, 20.2%) ( p < 0.001), and grade 1 (EEC G1) (17/93, 18.3%) ( p < 0.001). Of EEC G3 tumors, patients with MMR gene mutations were significantly older ( p = 0.024) or had lower BMI's than MMR mutation noncarriers ( p = 0.028). Of 562 endometrial carcinomas, alterations in MSH2 (n = 55), MSH6 (n = 54), MSH3 (n = 50) were the most frequent mutations. There were no differences in overall survival and progression-free interval between MMR mutation carriers and nonmutation carriers (p > 0.05) except that PFI with MMR gene mutation was higher than with MMR proficiency in EEC G3 ( p = 0.014). Conclusions: EEC G3 harbored the most MMR mutations among EC. EEC G3 and USC could be more considered to screen MMR mutation due to more MMR mutations occurred in EEC G3 and USC than did among EEC G2 and EEC G1. Besides MLH1, MSH2, MSH6, PMS2 and EPCAM mutation , MLH3, MSH3, PMS1 mutation could be screened in patients with newly diagnosed endometrial carcinoma. [Table: see text]