T-lymphoblastic lymphoma terminating as malignant histiocytosis with rearrangement of immunoglobulin heavy chain gene.

A 19-year-old man presented with cutaneous, mediastinal and intrapleural localization of a T-lymphoblastic non-Hodgkin's lymphoma (NHL) of immature phenotype. Two weeks after mediastinal irradiation the T-lymphoblasts had disappeared from the pleural effusion, but a clonal monocytic cell population was detected, as documented by immunological marker analysis and the presence of t(10;11), a cytogenetic aberration often associated with monocytic malignancies. Intensive chemotherapy induced a complete remission of the T-lymphoblastic NHL. However, the patient died from massive infiltration of lympho-hemopoietic tissue by cells with the morphology and immunological phenotype of macrophages. Southern blot analysis revealed the presence of a clonally rearranged immunoglobulin heavy chain (lgH) gene in tumorous tissue obtained at autopsy. The same clonally rearranged lgH was detectable in the post-irradiation pleural fluid 2 weeks after initial diagnosis. The observed germline configuration of T-cell receptor beta-genes and both lg light chain genes in this monoclonal proliferation provides additional evidence for the true histiocytic nature of the fatal disease. Therefore we conclude that a true histiocytic NHL with one rearranged lgH gene was most probably already present at initial diagnosis when the patient presented with the T-lymphoblastic NHL and that this true histiocytic NHL further developed despite the cytostatic treatment.