Primary lymphomas of bone.

Primary lymphomas of bone are uncommon malignancies. The vast majority of them are non-Hodgkin lymphoma (NHL), whereas primary Hodgkin lymphoma (HL) of bone is extremely rare. Patients with primary NHL of bone commonly present with local bone pain, soft tissue swelling, and a mass or a pathological fracture. There is a slight male preponderance, and most patients are over 45-50 years of age. Primary NHL of bone can arise in any part of the skeleton, but long bones (femurs, tibia) are the most common sites of presentation. Comprehensive immunohistochemical studies are required to establish an accurate histological diagnosis of primary NHL of bone. Most cases of primary NHL of bone are classified as diffuse large B-cell lymphomas (DLBCL) in the World Health Organisation (WHO) classification of hematological malignancies. On full staging evaluation, most patients have disease of stage IE or IIE according to the Ann Arbor system. Several studies indicate that patients with primary NHL of bone have a favorable outcome, especially when treated by combined modality therapy. A number of studies reported that clinical stage is the most important prognostic variable in predicting overall survival. Interestingly, the rare occurrence of primary lymphoma of bone is in contrast with the frequency of plasma cell tumors in bone. This could be due to the fact that, during normal B-cell differentiation, the bone marrow is the normal site of homing of plasma cells which are terminally-differentiated, immunoglobulin-secreting post-germinal center B-cells. In this respect, there is circumstancial evidence that primary NHL of bone may represent tumors of post-germinal center B-cells. The present review summarizes data on the histogenesis of primary NHL of bone in view of the recent histogenetic classification of DLBCL on the basis of the B-cell differentiation gene expression profiles (germinal center vs. post-germinal center B-cell differentiation).