Immunoblastic sarcoma and rheumatoid arthritis.

Introduction Immunoblast was the name proposed by Dameshek in 1963 to describe an antigenically "switched on" or transformed lymphocyte. Band T immunoblasts develop when the corresponding small resting lymphocyte is stimulated. The B immunoblasts further mature into plasma cells and both have been shown to produce antibodies after antigen stimulation• Lukes and CoIlins 4, by correlating immunological function with microscopic appearance, proposed a classification of lymphomas in which they recognised a highly malignant tumour composed of proliferating immunoblasts. This they called immunoblastic sarcoma (lBS). Several of their patients gave a history of a chronic immune disorder, for example, rheumatoid arthritis or systemic lupus erythematosus. They suggested that an abnormal immune system in some way predisposed to the development of this lymphoma. The classification and nomenclature of the non-Hodgkin's lymphomas is controversial5• The Rappaport6 classification (Table I), based exclusively on morphology, includes a group of "histiocytic" lymphomas (reticulum cell sarcoma). However, when immunological methods are applied to these so-called histiocytic lymphomas, the majority are found to be tumours of transformed lymphocytes, most commonly of "B" cell lineage7• True histiocytic lymphomas are rare• Reticulum cell sarcomas (or "histiocytic" lymphomas of Rappaport) have beed reported in patients with Hashimoto's thyroiditis, Sjogrens syndrome, coeliac disease10 and renal transplant recipients, all conditions in which there is ari! abnormality of the immune system. As the majority of these tumours are derived from "B" lymphocytes and many of them closely resemble immunoblastic sarcoma it may be that IBS is more common than previously appreciated. Indeed, Lukes and Tindle have suggested that "reticulum cell sarcomas" arising from transplant patients are in fact examples of IBS. A patient is described who developed IBS within a short time of the onset of rheumatoid a:rthri tis.