Progression of an orbital T-cell rich B-cell lymphoma to a B-cell lymphomain a dog

An 11-year-old Shetland Sheepdog was presented for exophthalmos caused by a locally extensive, poorly defined mass located behind the right eye. The p rimary orbital mass was identified by light microscopy and immunohistochemi stry as a T-cell rich B-cell lymphoma (TCRBCL) composed predominantly of BL A.36-positive large neoplastic lymphoid cells admired with fewer CD3- and C D79a-positive small lymphocytes. The dog was treated fur lymphoma, but 6 mo nths after presentation it was euthanatized for suspected hepatic and gastr ointestinal metastasis. Gross findings revealed an enlarged liver with mult iple well-demarcated, randomly distributed 0.1-1.5-cm white nodules, five f irm white submucosal jejunal nodules, and ileocecal, mediastinal, and hilar lymphadenopathy. Metastatic liver lesions consisted of sheets of monomorph ic large neoplastic lymphoid cells that effaced and expanded por tal and ce ntrilobular zones. These cells were morphologically similar to the large ne oplastic cells of the original orbital tumor and were CD3-negative and vari ably BLA.36-positive, consistent with B-cell lineage. Similar cells compris ed the jejunal nodules and effaced the lymph nodes. The progression of TCRB CL to a diffuse B-cell lymphoma in this case is consistent with reported hu man cases and has not been previously reported in the dog.