The Challenge of Diagnosing Constitutional Mismatch Repair Deficiency Syndrome in Brain Malignancies from Young Individuals

Therapeutically targeting the unique disease landscape of pediatric high-grade gliomas

Pediatric high-grade gliomas (pHGG) are a rare yet devastating malignancy of the central nervous system's glial support cells, affecting children, adolescents, and young adults. Tumors of the central nervous system account for the leading cause of pediatric mortality of which high-grade gliomas present a significantly grim prognosis. While the past few decades have seen many pediatric cancers experiencing significant improvements in overall survival, the prospect of survival for patients diagnosed with pHGGs has conversely remained unchanged. This can be attributed in part to tumor heterogeneity and the existence of the blood-brain barrier. Advances in discovery research have substantiated the existence of unique subgroups of pHGGs displaying alternate responses to different therapeutics and varying degrees of overall survival. This highlights a necessity to approach discovery research and clinical management of the disease in an alternative subtype-dependent manner. This review covers traditional approaches to the therapeutic management of pHGGs, limitations of such methods and emerging alternatives. Novel mutations which predominate the pHGG landscape are highlighted and the therapeutic potential of targeting them in a subtype specific manner discussed. Collectively, this provides an insight into issues in need of transformative progress which arise during the management of pHGGs.

Constitutional Mismatch Repair Deficiency Syndrome as a Cause of Numerous Malignancies in a Teenage Patient-A Case Report

Constitutional mismatch repair deficiency syndrome is a genetic disorder resulting from a biallelic mutation in one of the following genes: MLH1, MSH2, MSH6, or PMS2. Individuals with constitutional mismatch repair deficiency are highly predisposed to develop both hematological and solid cancers in childhood, particularly lymphoma, brain tumors, and gastrointestinal neoplasms. We report a case of a boy diagnosed with B-cell acute lymphoblastic leukemia at the age of 3. In 2013, at the age of 6, head magnetic resonance imaging revealed hamartoma and astrocytoma lesions in the central nervous system. Two years after treatment completion, a diagnosis of precursor T-cell lymphoblastic lymphoma, accompanied by the vena cava syndrome, was established and treated accordingly. During treatment, a genetic test using Sanger sequencing was performed-a biallelic mutation in the MSH6 gene was detected. The study revealed that the mutation 17-bp c.2277-2293del. was inherited from the patient's mother. The second mutation, 5-bp c.1135_1139delAGAGA, developed inpatient de novo. At the age of 14, the diagnosis of isolated bone marrow relapse of acute lymphoblastic leukemia B-cell type was established. Due to the almost exceeded total dose of anthracyclines, the patient's treatment included blinatumomab, and subsequently, he was qualified for allogeneic hematopoietic cell transplantation. The patient remains in complete remission for 11 months after allogeneic hematopoietic stem cell transplantation under the care of the transplant center.

Constitutional mismatch repair deficiency syndrome with atypical features caused by a homozygous MLH1 missense variant (c.1918C>A, p.(Pro640Thr)): a case report

Constitutional mismatch repair deficiency (CMMRD) syndrome is a rare autosomal recessive genetic disorder caused by biallelic germline mutations in one of the mismatch repair genes. Carriers are at exceptionally high risk for developing, typically in early life, hematological and brain malignancies, as well as cancers observed in Lynch syndrome. We report a homozygous MLH1 missense variant (c.1918C>A p.(Pro640Thr)) in a Tunisian patient with CMMRD syndrome and a family history of early-age colorectal cancer. The proband presented initially with colonic oligopolyposis and adenosquamous carcinoma of the caecum. He later developed several malignancies, including undifferentiated carcinoma of the parotid, grade 4 IDH-mutant astrocytoma, and ampulla of Vater adenocarcinoma. The patient was older than typical for this disease and had a remarkably prolonged survival despite developing four distinct aggressive malignancies. The current report highlights the challenges in assessing the pathogenicity of the identified variant and the remarkable phenotypic diversity in CMMRD.

Case Report: Malignant Brain Tumors in Siblings With MSH6 Mutations

Background

Familial brain tumor incidences are low. Identifying the genetic alterations of familial brain tumors can help better understand the pathogenesis and make therapy regimens for these tumors.

Case Presentation

An elder female and a younger male were diagnosed with brain tumors at the age of 10 and 5, respectively. Whole-genome sequencing analysis of the two patients’ blood, primary brain tumor tissues, and their parents’ blood samples was performed, which revealed that the two tumor samples harbored extremely high somatic mutation loads. Additionally, we observed pigmentation on the male patient’s skin.

Conclusion

Germline, biallelic mutation of MSH6—a gene related to DNA mismatch repair whose defect will result in constitutional mismatch repair deficiency (CMMRD)—is causal for the brain tumors of these two siblings.

Hypermutation as a potential predictive biomarker of immunotherapy efficacy in high-grade gliomas: a broken dream?

A high tumor mutational burden and mismatch repair deficiency are observed in 'hypermutated' high-grade gliomas (HGGs); however, the molecular characterization of this distinct subtype and whether it predicts the response to immune checkpoint inhibitors (ICIs) are largely unknown. Pembrolizumab is a valid therapeutic option for the treatment of hypermutated cancers of diverse origin, but only a few clinical trials have explored the activity of ICIs in hypermutated HGGs. HGGs appear to differ from other cancers, likely due to the prevalence of subclonal versus clonal neoantigens, which are unable to elicit an immune response with ICIs. The main aim of this review is to summarize the current knowledge on hypermutation in HGGs, focusing on the broken promises of tumor mutational burden and mismatch repair deficiency as potential biomarkers of response to ICIs.

Mismatch repair deficiency in early‐onset duodenal, ampullary, and pancreatic carcinomas is a strong indicator for a hereditary defect

Mismatch repair deficiency (dMMR) is a hallmark of Lynch syndrome (LS), but its prevalence in early‐onset (diagnosed under the age of 50 years) duodenal, ampullary, and pancreatic carcinomas (DC, AC, and PC, respectively) is largely unknown. We explored the prevalence of dMMR and the underlying molecular mechanisms in a retrospectively collected cohort of 90 early‐onset carcinomas of duodenal, ampullary, and pancreatic origin. dMMR was most prevalent in early‐onset DCs (47.8%); more than half of those were associated with hereditary cancer syndromes (LS or constitutional mismatch repair deficiency syndrome). All dMMR AC and PC were due to LS. Concordance of dMMR with underlying hereditary condition warrants ubiquitous dMMR testing in all early‐onset DC, AC, and PC.