HGG-03. PREVALENCE OF BIALLELIC MISMATCH REPAIR DEFICIENCY IN CHILDREN WITH MALIGNANT GLIOMA TREATED AT KING FAHAD MEDICAL CITY (KFMC). Issue 2 (22nd June 2018) - Mobark, Nahla Ali
Abstract: Hereditary Constitutional mismatch repair -deficiency (CMMR-D) caused by biallelic mutations in one or more MMR genes a cancer predisposition syndrome with features of neurofibromatosis type 1, often café-au-lait macule, development of different types of cancers in multiple organs. Given the high rate of consgunity in our population, we measure the prevalence of CMMR-D in our pediatric population with gliomas treated at our institution. We retrospectively analyzed demographic, immunohistochemistry, and molecular data for 31 cases diagnosed to have HGG and at KFMC between December 2006 and December 2016. Of the 31 patients (64.5 %) were boys and (35.5 %) girls. The median age at diagnosis was 11 years (range 2 - 17years). The most common pathological subtype was: Glioblastoma (58%) followed by Anaplastic Astrocytoma (19.4%). MMRD was observed in 19.4% of cases. There was no significant difference in the median survival time between MMR-D deficiency cases (1.78 years) and other cases (1.27 year). This is the first study to measure prevalence of CMMRD in Saudi Arabia which is known to have a high rate of consanguineous families. Our data showed around 20% of high grade glioma patients has CMMRD which is confirmed by two testing approaches: immunohistochemistry and molecular. In the era of immunotherapy, identifying CMMRD cases is critical as it opens new avenues for treatment options with check point inhibitors. Limitations in our study including small sample size and retrospective design and future prospective studies with larger sample size will be needed to confirm our results.