RESUMEN
@#Constitutionalmismatch repair deficiency(CMMRD) is a hereditary predisposition of malignancy evident in childhood leukemias, lymphomas, and malignant tumors of the brain, GI tract. It is a very rare condition that affects 1 per 1 million patients. Patients with CMMRD syndrome may also manifest with Neurofibromatosis Type 1 (NF1) phenotypic features, and benign masses, particularly in the gastrointestinal tract. This is a case of a 12-year old male who presented with phenotypic features of NF1, developed Acute Lymphoblastic Leukemia at 7 years old and went into remission. He subsequently developed synchronous Glioblastoma and Poorly differentiated Adenocarcinoma of the rectum.This report aims to raise awareness regarding the possibility of a CMMRD syndrome in pediatric patients who present with phenotypic features of NF1, and in those patients who present with two or more malignancies in their lifetime.