PMS2 mutation spectra in Norway and risk of cancer for carriers of pathogenic variants.

BACKGROUND: In Norway, we have offered testing of PMS2 since 2006, and have a large national cohort of carriers. The aim of this study was to describe all PMS2 variants identified, and to describe frequency, spectrum and penetrance of cancers in carriers of class 4/5 variants. METHODS: All detected PMS2 variants were collected from the diagnostic laboratories and reclassified according to ACMG criteria and gene specific guidelines. Data on variant, gender, cancer diagnosis, age at diagnosis, and age at last known follow-up was collected on all carriers of class 4/5 variants from electronic patient records. The Kaplan-Meier algorithm was used to calculate cumulative risk of any cancer, colorectal cancer and endometrial cancer. RESULTS: In total, 220 different PMS2 variants were detected. Twenty nine class 4/5 variants were identified in 482 carriers. The most common pathogenic variant was the founder mutation c.989-1G > T, detected in 204 patients from 58 families. Eighty seven out of 482 (18.0%) had been diagnosed with colorectal cancer, 10 of these (11.8%) before 40 years. Cumulative risk at 70 years in our cohort was 34.7% for colorectal cancer and 26.1% for endometrial cancer. CONCLUSIONS: After 15 years of genetic testing, 29 different class 4/5 variants have been detected in Norway. Almost half of Norwegian PMS2 carriers have the founder variant 989-1G > T. Penetrance of colorectal cancer in our cohort was moderate but variable, as 11.5% of those diagnosed were younger than 40 years.

Functions of PMS2 and MLH1 important for regulation of divergent repeat-mediated deletions.

Repeat-mediated deletions (RMDs) are a type of deletion rearrangement that utilizes two repetitive elements to bridge a DNA double-strand break (DSB) that leads to loss of the intervening sequence and one of the repeats. Sequence divergence between repeats causes RMD suppression and indeed this divergence must be resolved in the RMD products. The mismatch repair factor, MLH1, was shown to be critical for both RMD suppression and a polarity of sequence divergence resolution in RMDs. Here, we sought to study the interrelationship between these two aspects of RMD regulation (i.e., RMD suppression and polar divergence resolution), by examining several mutants of MLH1 and its binding partner PMS2. To begin with, we show that PMS2 is also critical for both RMD suppression and polar resolution of sequence divergence in RMD products. Then, with six mutants of the MLH1-PMS2 heterodimer, we found several different patterns: three mutants showed defects in both functions, one mutant showed loss of RMD suppression but not polar divergence resolution, whereas another mutant showed the opposite, and finally one mutant showed loss of RMD suppression but had a complex effect on polar divergence resolution. These findings indicate that RMD suppression vs. polar resolution of sequence divergence are distinct functions of MLH1-PMS2.

Evaluation of pathogenic variants detected in high homology regions of the PMS2 gene. How effective is long-range PCR?

Introduction: Lynch syndrome (LS) is an inherited cancer predisposition syndrome characterized by a high risk of colorectal and extracolonic tumors. Germline pathogenic variants (GPV) in the PMS2 gene are associated with <15% of all cases. The PMS2CL pseudogene presents high homology with PMS2, challenging molecular diagnosis by next-generation sequencing (NGS). Due to the high methodological complexity required to distinguish variants between PMS2 and PMS2CL, most laboratories do not clearly report the origin of this molecular finding. Objective: The aim of this study was to confirm the GPVs detected by NGS in regions of high homology segments of the PMS2 gene in a Brazilian sample. Methods: An orthogonal and gold standard long-range PCR (LR-PCR) methodology to separate variants detected in the PMS2 gene from those detected in the pseudogene. Results: A total of 74 samples with a PMS2 GPV detected by NGS in exons with high homology with PMS2CL pseudogene were evaluated. The most common was NM_000535.6:c.2182_2184delinsG, which was previously described as deleterious mutation in a study of African-American patients with LS and has been widely reported by laboratories as a pathogenic variant associated with the LS phenotype. Of all GPVs identified, only 6.8% were confirmed by LR-PCR. Conversely, more than 90% of GPV were not confirmed after LR-PCR, and the diagnosis of LS was ruled out by molecular mechanisms associated with PMS2. Conclusion: In conclusion, the use of LR-PCR was demonstrated to be a reliable approach for accurate molecular analysis of PMS2 variants in segments with high homology with PMS2CL. We highlight that our laboratory is a pioneer in routine diagnostic complementation of the PMS2 gene in Brazil, directly contributing to a more assertive molecular diagnosis and adequate genetic counseling for these patients and their families.

Misclassification of a frequent variant from PMS2CL pseudogene as a PMS2 loss of function variant in Brazilian patients.

PMS2, a Lynch Syndrome gene, presents challenges in genetic testing due to the existence of multiple pseudogenes. This study aims to describe a series of cases harboring a variant in the PMS2CL pseudogene that has been incorrectly assigned to PMS2 with different nomenclatures. We reviewed data from 647 Brazilian patients who underwent multigene genetic testing at a single center to identify those harboring the PMS2 V1:c.2186_2187delTC or V2:c.2182_2184delACTinsG variants, allegedly located at PMS2 exon 13. Gene-specific PCR and transcript sequencing was performed. Among the 647 individuals, 1.8% (12) carried the investigated variants, with variant allele frequencies ranging from 15 to 34%. By visually inspecting the alignments, we confirmed that both V1 and V2 represented the same variant and through gene-specific PCR and PMS2 transcript analysis, we demonstrated that V1/V2 is actually located in the PMS2CL pseudogene. Genomic databases (ExAC and gnomAD) report an incidence of 2.5 - 5.3% of this variant in the African population. Currently, V1 is classified as "uncertain significance" and V2 as "conflicting" in ClinVar, with several laboratories classifying them as "pathogenic". We identified a frequent African PMS2CL variant in the Brazilian population that is misclassified as a PMS2 variant. It is likely that V1/V2 have been erroneously assigned to PMS2 in several manuscripts and by clinical laboratories, underscoring a disparity-induced matter. Considering the limitations of short-read NGS differentiating between certain regions of PMS2 and PMS2CL, using complementary methodologies is imperative to provide an accurate diagnosis.

MutLα suppresses error-prone DNA mismatch repair and preferentially protects noncoding DNA from mutations.

The DNA mismatch repair (MMR) system promotes genome stability and protects humans from certain types of cancer. Its primary function is the correction of DNA polymerase errors. MutLα is an important eukaryotic MMR factor. We have examined the contributions of MutLα to maintaining genome stability. We show here that loss of MutLα in yeast increases the genome-wide mutation rate by ∼130-fold and generates a genome-wide mutation spectrum that consists of small indels and base substitutions. We also show that loss of yeast MutLα leads to error-prone MMR that produces T > C base substitutions in 5'-ATA-3' sequences. In agreement with this finding, our examination of human whole-genome DNA sequencing data has revealed that loss of MutLα in induced pluripotent stem cells triggers error-prone MMR that leads to the formation of T > C mutations in 5'-NTN-3' sequences. Our further analysis has shown that MutLα-independent MMR plays a role in suppressing base substitutions in N3 homopolymeric runs. In addition, we describe that MutLα preferentially protects noncoding DNA from mutations. Our study defines the contributions of MutLα-dependent and independent mechanisms to genome-wide MMR.

Therapeutic validation of MMR-associated genetic modifiers in a human ex vivo model of Huntington disease.

The pathological huntingtin (HTT) trinucleotide repeat underlying Huntington disease (HD) continues to expand throughout life. Repeat length correlates both with earlier age at onset (AaO) and faster progression, making slowing its expansion an attractive therapeutic approach. Genome-wide association studies have identified candidate variants associated with altered AaO and progression, with many found in DNA mismatch repair (MMR)-associated genes. We examine whether lowering expression of these genes affects the rate of repeat expansion in human ex vivo models using HD iPSCs and HD iPSC-derived striatal medium spiny neuron-enriched cultures. We have generated a stable CRISPR interference HD iPSC line in which we can specifically and efficiently lower gene expression from a donor carrying over 125 CAG repeats. Lowering expression of each member of the MMR complexes MutS (MSH2, MSH3, and MSH6), MutL (MLH1, PMS1, PMS2, and MLH3), and LIG1 resulted in characteristic MMR deficiencies. Reduced MSH2, MSH3, and MLH1 slowed repeat expansion to the largest degree, while lowering either PMS1, PMS2, or MLH3 slowed it to a lesser degree. These effects were recapitulated in iPSC-derived striatal cultures where MutL factor expression was lowered. CRISPRi-mediated lowering of key MMR factor expression to levels feasibly achievable by current therapeutic approaches was able to effectively slow the expansion of the HTT CAG tract. We highlight members of the MutL family as potential targets to slow pathogenic repeat expansion with the aim to delay onset and progression of HD and potentially other repeat expansion disorders exhibiting somatic instability.

Incidences of colorectal adenomas and cancers under colonoscopy surveillance suggest an accelerated "Big Bang" pathway to CRC in three of the four Lynch syndromes.

BACKGROUND: Colorectal cancers (CRCs) in the Lynch syndromes have been assumed to emerge through an accelerated adenoma-carcinoma pathway. In this model adenomas with deficient mismatch repair have an increased probability of acquiring additional cancer driver mutation(s) resulting in more rapid progression to malignancy. If this model was accurate, the success of colonoscopy in preventing CRC would be a function of the intervals between colonoscopies and mean sojourn time of detectable adenomas. Contrary to expectations, colonoscopy did not decrease incidence of CRC in the Lynch syndromes and shorter colonoscopy intervals have not been effective in reducing CRC incidence. The prospective Lynch Syndrome Database (PLSD) was designed to examine these issues in carriers of pathogenic variants of the mis-match repair (path_MMR) genes. MATERIALS AND METHODS: We examined the CRC and colorectal adenoma incidences in 3,574 path_MLH1, path_MSH2, path_MSH6 and path_PMS2 carriers subjected to regular colonoscopy with polypectomy, and considered the results based on sojourn times and stochastic probability paradigms. RESULTS: Most of the path_MMR carriers in each genetic group had no adenomas. There was no association between incidences of CRC and the presence of adenomas. There was no CRC observed in path_PMS2 carriers. CONCLUSIONS: Colonoscopy prevented CRC in path_PMS2 carriers but not in the others. Our findings are consistent with colonoscopy surveillance blocking the adenoma-carcinoma pathway by removing identified adenomas which might otherwise become CRCs. However, in the other carriers most CRCs likely arised from dMMR cells in the crypts that have an increased mutation rate with increased stochastic chaotic probabilities for mutations. Therefore, this mechanism, that may be associated with no or only a short sojourn time of MSI tumours as adenomas, could explain the findings in our previous and current reports.

PMS2 amplification contributes brain metastasis from lung cancer.

BACKGROUND: Lung adenocarcinoma metastasizing to the brain results in a notable increase in patient mortality. The high incidence and its impact on survival presents a critical unmet need to develop an improved understanding of its mechanisms. METHODS: To identify genes that drive brain metastasis of tumor cells, we collected cerebrospinal fluid samples and paired plasma samples from 114 lung adenocarcinoma patients with brain metastasis and performed 168 panel-targeted gene sequencing. We examined the biological behavior of PMS2 (PMS1 Homolog 2)-amplified lung cancer cell lines through wound healing assays and migration assays. In vivo imaging techniques are used to detect fluorescent signals that colonize the mouse brain. RNA sequencing was used to compare differentially expressed genes between PMS2 amplification and wild-type lung cancer cell lines. RESULTS: We discovered that PMS2 amplification was a plausible candidate driver of brain metastasis. Via in vivo and in vitro assays, we validated that PMS2 amplified PC-9 and LLC lung cancer cells had strong migration and invasion capabilities. The functional pathway of PMS2 amplification of lung cancer cells is mainly enriched in thiamine, butanoate, glutathione metabolism. CONCLUSION: Tumor cells elevated expression of PMS2 possess the capacity to augment the metastatic potential of lung cancer and establish colonies within the brain through metabolism pathways.

Identification of a Catalytic Lysine Residue Conserved Among GHKL ATPases: MutL, GyrB, and MORC.

DNA mismatch repair endonuclease MutL is a member of GHKL ATPase superfamily. Mutations of MutL homologs are causative of a hereditary cancer, Lynch syndrome. We characterized MutL homologs from human and a hyperthermophile, Aquifex aeolicus, (aqMutL) to reveal the catalytic mechanism for the ATPase activity. Although involvement of a basic residue had not been conceived in the catalytic mechanism, analysis of the pH dependence of the aqMutL ATPase activity revealed that the reaction is catalyzed by a residue with an alkaline pKa. Analyses of mutant aqMutLs showed that Lys79 is the catalytic residue, and the corresponding residues were confirmed to be critical for activities of human MutL homologs, on the basis of which a catalytic mechanism for MutL ATPase is proposed. These and other results described here would contribute to evaluating the pathogenicity of Lynch syndrome-associated missense mutations. Furthermore, it was confirmed that the catalytic lysine residue is conserved among DNA gyrases and microrchidia ATPases, other members of GHKL ATPases, indicating that the catalytic mechanism proposed here is applicable to these members of the superfamily.

In vitro data suggest a role for PMS2 Kozak sequence mutations in Lynch syndrome risk.

Lynch syndrome (LS) is the most common hereditary cancer syndrome. Heterozygous loss-of-function variants in PMS2 are linked to LS. While these variants are not directly cancer causing, reduced PMS2 function results in the accumulation of somatic variants and increased cancer risk over time due to DNA mismatch repair dysfunction. It is reasonable that other types of genetic variation that impact the expression of PMS2 may also contribute to cancer risk. The Kozak sequence is a highly conserved translation initiation motif among higher eukaryotes and is defined as the nine base pairs upstream of the translation start codon through the first four bases of the translated sequence (5'-[GTT]GCATCCATGG-3'; human PMS2: NM_000535.7). While Kozak sequence variants in PMS2 have been reported in ClinVar in patients with suspected hereditary cancer, all variants upstream of the translation start site are currently classified as variants of undetermined significance (VUSs). We hypothesized that variants significantly disrupting the Kozak sequence of PMS2 would decrease PMS2 protein expression, contributing to increased cancer risk over time. Using a dual-luciferase reporter plasmid and site-directed mutagenesis, we generated the wild-type human PMS2 and the ClinVar VUSs within the PMS2 Kozak sequence. Besides the c.1A>C variant, which is already known to be pathogenic, we implicate six additional variants as American College of Medical Genetics and Genomics (ACMG)/Association for Molecular Pathology (AMP) pathogenic supporting (PP) variants and classify ten as benign supporting (BP). In summary, we present a method developed for the classification of human PMS2 Kozak sequence variants that can contribute to the re-classification of VUSs identified in patients.

Comparison of Microsatellite Instability With Clinicopathologic Data in Patients With Colon Adenocarcinoma.

Background Microsatellite instability (MSI) is a genetic condition caused by errors in DNA repair genes that cause colorectal cancer (CRC). The literature contradicts the frequency of MSI in sporadic CRCs and its effect on prognosis. This study investigated the distribution of clinicopathologic features and the relationship between MSI and survival outcomes. Methodology This is a retrospective study of 101 consecutive cases of CRC and immunohistochemical studies. All cases were retrospectively reviewed and reevaluated by histological grade, lymphovascular invasion, perineural invasion, tumor borders, dirty necrosis, tumor-infiltrating lymphocytes (TILs), Crohn's-like lymphoid reaction, mucinous and medullary differentiation, and tumoral budding from pathological slides. An immunohistochemical study was performed in appropriate blocks for using MLH-1, MSH-2, MSH-6, and PMS-2. We collected the clinical stage, pathological tumor stage, lymph node metastasis, age, sex, tumor diameter, distant metastasis, localization, and survival information from patients' clinical data. Results There was no statistically significant difference between the two groups regarding age, gender, tumor diameter, histological grade, tumor border, dirty necrosis, TILs, N and M stage, perineural and lymphovascular invasion, mucinous differentiation, medullary differentiation, and tumor budding characteristics of the patients. The MSI-H group was more frequently located in the right colon and transverse colon (p < 0.001), and the T stage was higher among them than in the MSI-L group (p = 0.014). Upon multivariate regression analysis, MSI status had no significant effect on survival time. Age and stage N and M were independent prognostic factors for colon cancer prognosis. Conclusions Our study presented the distribution of clinicopathological features and their relationship with MSI for 101 regional CRC patients. MSI status was detected by immunohistochemistry. Identifying MSI in CRCs may help personalize therapy planning. As the distribution of the features may vary from population to population, further investigations are needed on this topic.

MRE11A: a novel negative regulator of human DNA mismatch repair.

BACKGROUND: DNA mismatch repair (MMR) is a highly conserved pathway that corrects DNA replication errors, the loss of which is attributed to the development of various types of cancers. Although well characterized, MMR factors remain to be identified. As a 3'-5' exonuclease and endonuclease, meiotic recombination 11 homolog A (MRE11A) is implicated in multiple DNA repair pathways. However, the role of MRE11A in MMR is unclear. METHODS: Initially, short-term and long-term survival assays were used to measure the cells' sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Meanwhile, the level of apoptosis was also determined by flow cytometry after MNNG treatment. Western blotting and immunofluorescence assays were used to evaluate the DNA damage within one cell cycle after MNNG treatment. Next, a GFP-heteroduplex repair assay and microsatellite stability test were used to measure the MMR activities in cells. To investigate the mechanisms, western blotting, the GFP-heteroduplex repair assay, and chromatin immunoprecipitation were used. RESULTS: We show that knockdown of MRE11A increased the sensitivity of HeLa cells to MNNG treatment, as well as the MNNG-induced DNA damage and apoptosis, implying a potential role of MRE11 in MMR. Moreover, we found that MRE11A was largely recruited to chromatin and negatively regulated the DNA damage signals within the first cell cycle after MNNG treatment. We also showed that knockdown of MRE11A increased, while overexpressing MRE11A decreased, MMR activity in HeLa cells, suggesting that MRE11A negatively regulates MMR activity. Furthermore, we show that recruitment of MRE11A to chromatin requires MLH1 and that MRE11A competes with PMS2 for binding to MLH1. This decreases PMS2 levels in whole cells and on chromatin, and consequently comprises MMR activity. CONCLUSIONS: Our findings reveal that MRE11A is a negative regulator of human MMR.

Genotype-phenotype correlations in carriers of the PMS2 founder variant c.1831dup.

BACKGROUND: Lynch syndrome represents one of the most common cancer predispositions worldwide and is caused by germline pathogenic variants (PV) in DNA mismatch repair (MMR) genes. We repeatedly identified a PV in the MMR gene PMS2, c.1831dup, accounting for 27% of all Swiss PMS2 PV index patients identified. Notably, 2/18 index patients had been diagnosed with colorectal cancer (CRC) before age 30. METHODS: In this study, we investigated if this PV could (i) represent a founder variant by haplotype analysis and (ii) be associated with a more severe clinical phenotype. RESULTS: Haplotype analysis identified a shared common region of about 0.7 Mb/1.3 cM in 13 (81%) out of 16 index patients. Genotype-phenotype correlations, combining data from the 18 Swiss and 18 literature-derived PMS2 c.1831dup PV index patients and comparing them to 43 Swiss index patients carrying other PMS2 PVs, indicate that the PMS2 c.1831dup variant may be associated with earlier (<50 y) age at CRC diagnosis (55% vs. 29%, respectively; p = 0.047). Notably, 30% (9/30) of cancers from c.1831dup carriers displayed atypical MMR protein expression patterns on immunohistochemistry. CONCLUSION: Our results suggest that the PMS2 c.1831dup PV represents a, probably ancient, founder mutation and is possibly associated with an earlier CRC diagnosis compared to other PMS2 PVs.

PMS2 or PMS2CL? Characterization of variants detected in the 3' of the PMS2 gene.

PMS2 germline pathogenic variants are one of the major causes for Lynch syndrome and constitutional mismatch repair deficiencies. Variant identification in the 3' region of this gene is complicated by the presence of the pseudogene PMS2CL which shares a high sequence homology with PMS2. Consequently, short-fragment screening strategies (NGS, Sanger) may fail to discriminate variant's gene localization. Using a comprehensive analysis strategy, we assessed 42 NGS-detected variants in 76 patients and found 32 localized on PMS2 while 6 on PMS2CL. Interestingly, four variants were detected in either of them in different patients. Clinical phenotype was well correlated to genotype, making it very helpful in variant assessment. Our findings emphasize the necessity of more specific complementary analyses to confirm the gene origin of each variant detected in different individuals in order to avoid variant misinterpretation. In addition, we characterized two PMS2 genomic alterations involving Alu-mediated tandem duplication and gene conversion. Those mechanisms seemed to be particularly favored in PMS2 which contribute to frequent genomic rearrangements in the 3' region of the gene.

A Rare Variant in MDH2 (rs111879470) Is Associated with Predisposition to Recurrent Breast Cancer in an Extended High-Risk Pedigree.

A significant fraction of breast cancer recurs, with lethal outcome, but specific genetic variants responsible have yet to be identified. Five cousin pairs with recurrent breast cancer from pedigrees with a statistical excess of recurrent breast cancer were sequenced to identify rare, shared candidate predisposition variants. The candidates were tested for association with breast cancer risk with UKBiobank data. Additional breast cancer cases were assayed for a subset of candidate variants to test for co-segregation. Three-dimensional protein structure prediction methods were used to investigate how the mutation under consideration is predicted to change structural and electrostatic properties in the mutated protein. One hundred and eighty-one rare candidate predisposition variants were shared in at least one cousin pair from a high-risk pedigree. A rare variant in MDH2 was found to segregate with breast-cancer-affected relatives in one extended pedigree. MDH2 is an estrogen-stimulated gene encoding the protein malate dehydrogenase, which catalyzes the reversible oxidation of malate to oxaloacetate. The molecular simulation results strongly suggest that the mutation changes the NAD+ binding pocket electrostatics of MDH2. This small sequencing study, using a powerful approach based on recurrent breast cancer cases from high-risk pedigrees, identified a set of strong candidate variants for inherited predisposition for breast cancer recurrence, including MDH2, which should be pursued in other resources.

Mismatch Repair Deficient (dMMR) Colorectal Carcinoma in a Pakistani Cohort: Association With Clinical and Pathological Parameters.

Introduction Microsatellite instability (MSI) is an important pathway in colorectal carcinoma (CRC) pathogenesis. MSI occurs due to mutations in mismatch repair (MMR) genes that include MutL protein homolog 1 (MLH1), postmeiotic segregation increased 2 (PMS2), MutS homolog 2 (MSH2), and MutS homolog 6 (MSH6). CRC with MSI is termed MMR deficient (dMMR) CRC. Conversely, CRC with intact MMR genes is called microsatellite stable (MSS) or MMR proficient (pMMR). In this study, we compared the clinicopathological features of dMMR CRC with pMMR CRC. Methods It was a retrospective study conducted in the Department of Histopathology, Liaquat National Hospital, Karachi, Pakistan, from March 2020 to February 2022, over a duration of two years. Biopsy-proven cases of CRC with upfront surgical resection were included in the study. Microscopic examination was performed to evaluate tumor type, grade, and extent of invasion, presence of necrosis, perineural invasion (PNI), lymphovascular invasion (LVI), peritumoral lymphocytes (PTL), intratumoral lymphocytes (ITL), and nodal metastasis. Immunohistochemical staining was performed using antibodies, namely, MLH1, PMS2, MSH2, and MSH6. Any loss of nuclear expression in tumor cells was termed dMMR or microsatellite instable, whereas the intact nuclear expression in tumor cells was labeled as MSS or pMMR. Results A total of 135 cases of CRC were included in the study. The mean age at diagnosis was 46.76 ± 17.74 years, with female predominance (60.7%). The loss of MLH1, PMS2, MSH2, and MSH6 expression was noted in 39.3%, 34.1%, 17.8%, and 16.3% cases, respectively. Overall, 59.3% of CRCs were pMMR, while 40.7% were dMMR. A significant association of MMR status was noted with respect to age, PNI, LVI, tumor grade, tumor (T) and nodal (N) stage, mucinous differentiation, and ITL. dMMR CRC was significantly above 50 years than pMMR CRC. The frequency of PNI and LVI was lower in dMMR CRC than in pMMR CRC. Conversely, the higher grade (grade 3) and higher T-stage (T4) were associated with dMMR CRC. Alternatively, the frequency of higher N stage (N2b) was more commonly seen in pMMR CRC. Moreover, mucinous differentiation and ITL were significantly associated with dMMR CRC. Conclusion A significant proportion of CRC patients in our population demonstrated dMMR status. dMMR CRC had a higher histological grade with a higher frequency of mucinous differentiation and higher T-stage. Conversely, the presence of LVI, PNI, and higher N stages were associated with pMMR CRC.

Pakistan National Guidelines for Pediatric High-Grade Gliomas.

Pediatric high-grade glioma (pHGG) is highly malignant central nervous system tumor and constitute 10% of the pediatric gliomas. Effective treatment needs a functioning multi-disciplinary team including pediatric neuro oncologist, neurosurgeon, neuroradiologist, neuropathologist and radiation oncologist. Despite surgical resection, radiotherapy and chemotherapy, most HGG will recur resulting in early death. A significant proportion of HGG occurs in context of cancer predisposition syndromes like Constitutional Mismatch Repair Deficiency (CMMRD) also known as Biallelic Mismatch Repair Deficiency (bMMRD) characterized by high mutational burden. The incidence of HGG with CMMRD is one per million patients. bMMRD is caused by homozygous germline mutations in one of the four Mis Match Repair (MMR) genes (PMS2, MLH1, MSH2, and MSH6). The use of TMZ is now avoided in CMMRD related HGG due to its limited response and known ability to increase the accumulation of somatic mutations in these patients, increasing the risk of secondary tumors. HGG should be managed under the care of multidisciplinary team to receive optimum treatment. This is particularly important for low middle-income countries (LMIC) with limited resources like Pakistan.

Co-Occurrence of Germline Genomic Variants and Copy Number Variations in Hereditary Breast and Colorectal Cancer Patients.

Hereditary Breast and Ovarian Cancer (HBOC) syndrome is an autosomal dominant disease associated with a high risk of developing breast, ovarian, and other malignancies. Lynch syndrome is caused by mutations in mismatch repair genes predisposing to colorectal and endometrial cancers, among others. A rare phenotype overlapping hereditary colorectal and breast cancer syndromes is poorly characterized. Three breast and colorectal cancer unrelated patients fulfilling clinical criteria for HBOC were tested by whole exome sequencing. A family history of colorectal cancer was reported in two patients (cases 2 and 3). Several variants and copy number variations were identified, which potentially contribute to the cancer risk or prognosis. All patients presented copy number imbalances encompassing PMS2 (two deletions and one duplication), a known gene involved in the DNA mismatch repair pathway. Two patients showed gains covering the POLE2 (cases 1 and 3), which is associated with DNA replication. Germline potentially damaging variants were found in PTCH1 (patient 3), MAT1A, and WRN (patient 2). Overall, concurrent genomic alterations were described that may increase the risk of cancer appearance in HBOC patients with breast and colorectal cancers.

Early-Onset/Young-Onset Colorectal Carcinoma: A Comparative Analysis of Morphological Features and Biomarker Profile.

Introduction Colorectal carcinoma (CRC) is one of the most common cancers that involve the human body. Young-onset CRC (YO-CRC) or early-onset CRC (EO-CRC) is defined as CRC that develops before the age of 50 years, as opposed to CRC that is diagnosed after the age of 50, referred to as late-onset CRC (LO-CRC). EO-CRC is sparsely studied in our population. Therefore, in this study, we evaluated the clinicopathological parameters and biomarker profile of EO-CRC and compared them with those of LO-CRC. Methods This was a retrospective study conducted at the Department of Histopathology, Liaquat National Hospital, Karachi, Pakistan. A total of 254 biopsy-proven cases of CRC, reported over a period of nine years, were enrolled in the study. The specimens collected during surgery were sent to the laboratory for histopathological and immunohistochemical (IHC) status examinations. IHC staining of the specimens was performed using antibodies, namely, MutL protein homolog 1 (MLH1), postmeiotic segregation increased 2 (PMS2), MutS homolog 2 (MSH2), MutS homolog 6 (MSH6), and human epidermal growth factor receptor 2 (HER2/neu), on representative tissue blocks. A comparison of morphological and biomarker profiles between EO-CRC and LO-CRC was performed. Results The mean age at diagnosis was 46.27±17.75 years, with female predominance (59.8%). A significant difference between the two groups (EO-CRC and LO-CRC) was noted with respect to laterality, tumor site, tumor grade, tumor type, presence of pre-existing polyps, perineural invasion (PNI), lymphovascular invasion (LVI), and IHC markers. EO-CRC (as opposed to LO-CRC) significantly affected the left colon (92.6% vs. 72.9%, p<0.001), with the rectosigmoid being the most common site in the majority of cases (72.1% in EO-CRC vs. 61% in LO-CRC). EO-CRC showed a higher frequency of PNI and LVI than LO-CRC (42.6% vs. 23.7%, p=0.001; 29.4% vs. 18.6%, p=0.046, respectively). A significantly higher proportion of EO-CRCs were mucinous (42.6%) and medullary carcinoma (11.8%). Although the majority (54.4%) of cases of EO-CRC were grade 2 tumors at the time of diagnosis, a significantly higher proportion of them were grade 3 (44.1%) compared with LO-CRC. IHC comparisons between the two age groups showed that a significantly higher proportion of cases of EO-CRC showed positive HER2/neu expression (27.1%) compared with LO-CRC (13.2%). Conversely, the loss of expression of microsatellite instability (MSI) markers was more commonly seen in LO-CRS compared with EO-CRC. Conclusions We found a relatively higher frequency of EO-CRC in our population. Moreover, compared with LO-CRCs, EO-CRCs were associated with prognostically poor histological parameters, such as mucinous and medullary carcinoma, high-grade, PNI, and LVI. Similarly, EO-CRC had a higher positive expression of HER2/neu with intact MSI markers compared with AO-CRC; all these characteristics indicate poor biological behavior in EO-CRC.