Primary T cell/histiocyte-rich large B-cell lymphoma of the orbit.

T cell/histiocyte-rich large B-cell lymphoma (THRBCL) is an uncommon morphologic variant of diffuse large B-cell lymphoma characterized by a minor population of neoplastic B cells existing in a background of predominant reactive T lymphocytes. Diagnosis of this entity is occasionally difficult and would require careful immunohistochemical analysis of the tumor cells, as it may appear similar to other lymphoid diseases, such as nodular lymphocyte-predominant Hodgkin lymphoma, classical Hodgkin lymphoma, and peripheral T-cell lymphoma. The authors report a case of 37-year-old man who presented with a slowly growing, painless proptosis of the right eye with a well-defined mass in the posterosuperior aspect of globe. An incisional biopsy of the mass was performed. Histopathologic examination and immunohistochemical analysis revealed the diagnosis of THRBCL. To the best of the authors' knowledge, this is the first case of primary THRBCL occurring in the orbit.