Introduction Nijmegen breakage syndrome (NBS) is a rare autosomal recessive chromosome instability disorder characterized by microcephaly, growth retardation, abnormal facial appearance, immunodeficiency, radiation hypersensitivity, and congenital malformations. 1-5 The majority of known patients with NBS are of Slavic origin. 5 The NBS1 gene, responsible for the disease, is located on chromosome 8q21; its protein, nibrin, forms the MRE11/RAD50/NBS1 complex, which plays an important role in double-strand break DNA repair and the maintenance of chromosomal integrity. 6-9 Because of the ineffective DNA repair mechanisms, chromosomal aberrations accumulate, and immunodeficiency, malformations, and radiation hypersensitivity occur. This contributes to a high predisposition for the development of malignancies, particularly non-Hodgkin lymphoma (NHL), predominantly B-cell type, lymphoblastic leukemia, and Hodgkin lymphoma. Because of the cellular and humoral immunodeficiency, patients have recurring infections, which are typically community acquired and predominantly involve the respiratory tract. Approximately 40%-50% of patients reported to date had developed malignancies; a fatal outcome was noted in approximately 60% of them. Treatment can be difficult because of the increased sensitivity to ionizing radiation and radiomimetic drugs, requiring the use of a reduced dosage. 1-4,9-15 We report a 17-year old Croatian patient with NBS who developed B-cell NHL stage IV and who was successfully treated with rituximab in addition to the standard chemotherapy in a reduced dosage. Successful Treatment of Diffuse Large B-Cell Non-Hodgkin Lymphoma with Modified CHOP (Cyclophosphamide/Doxorubicin/Vincristine/ Prednisone) Chemotherapy and Rituximab in a Patient with Nijmegen Syndrome Miroslav Dumic, 1 Ivo Radman, 2 Nevena Krnic, 1 Marin Nola, 3 Rajko Kusec, 4 Davor Begovic, 1 Boris Labar, 2 Marko Rados 5 A 17-year-old Croatian boy with Nijmegen breakage syndrome (NBS) who developed diffuse large B-cell non-Hodgkin lymphoma is pre- sented. The majority of the patients with this rare autosomal recessive disease are of Slavic origin and, in most of them, the disease is caused by NBS1 mutation 657del5, as was found in our patient. Nijmegen breakage syndrome is characterized by microcephaly, growth retardation, abnormal facial appearance, spontaneous chromosomal rearrangements, immunodeficiency, and a high predisposition to cancer development, predominantly lymphoma. Because of increased sensitivity to radiation therapy and chemotherapy, the treatment of malignancies in patients with NBS can be difficult. To our knowledge, our patient is the first with NBS reported in the literature who was successfully treated for diffuse large B-cell lymphoma with the anti-CD20 monoclonal antibody rituximab in addition to a modified dose of CHOP (cyclophosphamide/doxorubicin/vincristine/prednisone) chemotherapy. He has been in complete remission for 3 years after finishing the treatment. Clinical Lymphoma & Myeloma, Vol. 7, No. 9, 590-593, 2007 Key words: Chromosomal breakage syndrome, DNA repair, Monoclonal antibody, NBS1 gene, Nibrin Abstract Case Report Address for correspondence: Miroslav Dumic, MD, PhD, Department of Pediatrics, University Hospital Center Zagreb, Kispaticeva 12, 10 000 Zagreb, Croatia Fax: 385-1-242-1894; e-mail: drdumic@mef.hr Submitted: Jul 10, 2007; Accepted: Aug 22, 2007 1 Department of Pediatrics 2 Department of Hematology 3 Department of Pathology University Hospital Center Zagreb, Croatia 4 Department of Medicine, University Hospital Dubrava, Croatia 5 Department of Radiology, University Hospital Center Zagreb, Croatia Electronic forwarding or copying is a violation of US and International Copyright Laws. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by CIG Media Group, LP, ISSN #1557-9190, provided the appropriate fee is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA 978-750-8400. 590 • Clinical Lymphoma & Myeloma November 2007