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

Biallelic germline mismatch repair (MMR) gene (MLH1, MSH2, MSH6, and PMS2) mutations are an extremely rare event that causes constitutional mismatch repair deficiency (CMMRD) syndrome. CMMRD is underdiagnosed and often debuts with pediatric malignant brain tumors. A high degree of clinical awareness of the CMMRD phenotype is needed to identify new cases. Immunohistochemical (IHC) assessment of MMR protein expression and analysis of microsatellite instability (MSI) are the first tools with which to initiate the study of this syndrome in solid malignancies. MMR IHC shows a hallmark pattern with absence of staining in both neoplastic and non-neoplastic cells for the biallelic mutated gene. However, MSI often fails in brain malignancies. The aim of this report is to draw attention to the peculiar IHC profile that characterizes CMMRD syndrome and to review the difficulties in reaching an accurate diagnosis by describing the case of two siblings with biallelic MSH6 germline mutations and brain tumors. Given the difficulties involved in early diagnosis of CMMRD we propose the use of the IHC of MMR proteins in all malignant brain tumors diagnosed in individuals younger than 25 years-old to facilitate the diagnosis of CMMRD and to select those neoplasms that will benefit from immunotherapy treatment.

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RARE-17. SURVIVAL BENEFIT FOR INDIVIDUALS WITH CONSTITUTIONAL MISMATCH REPAIR DEFICIENCY SYNDROME AND BRAIN TUMORS WHO UNDERGO SURVEILLANCE PROTOCOL. A REPORT FROM THE INTERNATIONAL REPLICATION REPAIR CONSORTIUM

Neuro-Oncology ◽

10.1093/neuonc/noaa222.728 ◽

2020 ◽

Vol 22 (Supplement_3) ◽

pp. iii445-iii446

Author(s):

Ayse Bahar Ercan ◽

Carol Durno ◽

Vanessa J Bianchi ◽

Melissa Edwards ◽

Melyssa Aronson ◽

...

Keyword(s):

Brain Tumors ◽

Mismatch Repair ◽

Survival Benefit ◽

Deficiency Syndrome ◽

Low Grade ◽

Mismatch Repair Deficiency ◽

Repair Deficiency ◽

Surveillance Protocol ◽

Total Body ◽

Constitutional Mismatch Repair Deficiency

Abstract BACKGROUND Constitutional mismatch repair deficiency syndrome (CMMRD) is a severe cancer predisposition syndrome resulting in early onset central nervous system (CNS) and other cancers. International guidelines for surveillance exist but no study has systematically evaluated the efficacy of this protocol. METHODS We surveyed all confirmed CMMRD patients in the International Replication Repair Deficiency Consortium. A surveillance protocol consisting of frequent biochemical, endoscopic and imaging (CNS and total body MRI) studies were employed. Survival analyses and efficacy of each method were assessed. RESULTS Surveillance data were collected from 105 CMMRD individuals from 41 countries. Of the 193 malignant tumors, CNS malignancies were the most common (44%). The surveillance protocol uncovered 49 asymptomatic tumors including 16 glioblastomas and medulloblastomas. Five-year overall survival was 89% for tumors discovered by surveillance, and 61% for symptomatic tumors (p<0.004). Similarly, 5-year survival was 82+/-11% and 24+/-6% for surveillance and non-surveillance of brain tumors (p=0.005). Yearly total body and q6 month brain MRI detected asymptomatic cancers in all but 3 symptomatic CNS gliomas. These were tumors uncovered when time between scans was >6 months as per protocol. Finally, of the low grade tumors identified asymptomatically, 5 were low grade gliomas. All of the low grade gliomas, which were not resected transformed to high grade tumors at a median of 1.6 ± 0.9 years. CONCLUSION These data support a survival benefit in CMMRD patients undergoing a surveillance protocol. Adherence to protocol and resection of lower grade lesions may improve survival for patients with CNS tumors.

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