RESUMEN

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. After treatment with chemotherapy and neurosurgery, haematopoietic stem cell transplant (HSCT) was performed. The second patient was diagnosed with mediastinal T-cell lymphoma at the age of two and a half years and a relapse at the age of four and a half years. He also received chemotherapy and underwent HSCT. Both patients exhibited café au lait macules (CALMs), a common but non-specific feature of CMMRD, often confused with neurofibromatosis type 1 (NF1) syndrome. This study highlights the phenotype of CMMRD syndrome, associated cancers, and the potential benefits of stem cell transplantation. Previous reports suggest that allogeneic HSCT might reduce subsequent haematological malignancies and increase survival.