Nijmegen breakage syndrome (NBS) is an inherited DNA repair disorder characterized by a high predisposition to develop lymphoid malignancies during childhood, with diffuse large B-cell lymphoma (DLBCL) being one of the leading types. Due to concomitant immunodeficiency and an increased risk of chemotherapy-induced toxicity, NBS patients often require modified and individualized cancer treatment. Nevertheless, they rarely achieve progressionand relapse-free long-term survival rates without hematopoietic stem cell transplantation. Unfavorable outcome of lymphomas in NBS may result not only from the reduction of drug dosages but could be associated with molecular aberrations occurring on the background of chromosomal instability. Therefore, we aimed to investigate clinical outcome, histopathological features, and genomic alterations of DLBCL in pediatric patients with NBS.