Clinical Insights and Potential Benefits of Stem Cell Transplantation for Constitutional Mismatch Repair Deficiency: A Case Report of Two Siblings.

Constitutional mismatch repair deficiency (CMMRD) syndrome, caused by biallelic mutations in mismatch repair genes, is one of the most aggressive hereditary cancer syndromes. This report presents the clinical course of two brothers diagnosed with CMMRD. The first patient was diagnosed with T-cell lymphoma at the age of three and a half years, a relapse, and synchronous glioblastoma at the age of seven and a half years.