Spontaneous chronic T-cell leukemia in a male rhesus macaque ( Macaca mulatta).

Blood smears from a 24-year-old male rhesus macaque ( Macaca mulatta) used for cognitive function studies were evaluated. The macaque had an 8-month history of gradual weight loss and increasing lymphocytosis. Most of the lymphocytes present were small to medium and had a mature morphology. Based on the degree and duration of the lymphocytosis, and the appearance of the lymphocytes, a diagnosis of chronic lymphocytic leukemia was made. The animal tested negative for 4 viral diseases that are commonly associated with lymphoproliferative disorders in Old World monkeys. Over the course of 12 months, the lymphocytosis progressed from 18.4 to 384 × 103 lymphocytes/µl (reference range: 0.8-17 × 103 cells/µl), and euthanasia was elected. On histologic examination, cluster of differentiation (CD)3- and CD8-positive, CD79-negative neoplastic cells comprised 40-60% of the bone marrow, diffusely obscured the normal splenic architecture, and were present in the vascular channels in other organs. Findings were characteristic of T-cell lymphocytic leukemia. Naturally occurring T-cell lymphocytic leukemia has been rarely reported in rhesus macaques and, to the authors' knowledge, never in males. A persistent lymphocytosis characterized by a monomorphic population of CD3- and CD8-positive cytotoxic T-lymphocytes and the presence of neoplastic cells in the bone marrow led to a diagnosis in the current case.

Spontaneous osteoblastic osteosarcoma in a Mongolian gerbil (Meriones unguiculatus).

Spontaneous neoplasms in Mongolian gerbils have an incidence of 20% to 26.8%, but osteosarcomas occur at a much lower rate. Here we report a 1-y-old Mongolian gerbil with a spontaneous osteosarcoma at the level of the proximal tibia, with metastases to the pectoral muscles and lungs. Grossly, the tibial mass obliterated the tibia and adjacent muscles, and an axillary mass with a bloody, cavitary center expanded the pectoral muscles. Microscopically, the tibial mass was an infiltrative, osteoblastic mesenchymal neoplasm, and the axillary mass was an anaplastic mesenchymal neoplasm with hemorrhage. The lung contained multiple metastatic foci. Immunohistochemistry for osteonectin was strongly positive in the tibial, axillary, and pulmonary metastases. Although osteosarcoma is the most common primary malignant bone neoplasm that occurs spontaneously in all laboratory and domestic animal species and humans, it arises less frequently than does other neoplasms. The current case of spontaneous osteoblastic osteosarcoma of the proximal tibia and metastases to the pectoral muscles and lung in a Mongolian gerbil is similar in presentation, histology, and predilection site of both osteoblastic and telangiectatic osteosarcomas in humans. In addition, this case is an unusual manifestation of osteosarcoma in the appendicular skeleton of a Mongolian gerbil.

Ameloblastic fibro-odontoma associated with a retained molar in an Oldenburg mare.

An 11-year-old Oldenburg mare presented with a 3-month history of weight loss and swelling of the posterior right mandible. Physical examination and radiographs showed a soft-tissue mass in the right mandible with foci of mineralization, periosteal proliferation, and a retained molar. The tumor increased in size over several weeks, and the mare was euthanized. On necropsy, a 24 cm × 15 cm × 15 cm firm, white mass had obliterated the posterior right mandible. The mass was multinodular with discrete clusters of blood-filled cystic spaces. Histologically, the mass was composed of neoplastic odontogenic epithelium and pulpal mesenchyme with an accumulation of eosinophilic material resembling dentin or enamel. Microscopic and immunohistochemical staining features of the neoplasm were most consistent with an ameloblastic fibro-odontoma.

Intrapericardial ectopic thyroid carcinoma in a cat.

A 7-year-old spayed female domestic shorthair feline presented with tachycardia and was later euthanized due to a declining condition. On gross examination, the thoracic cavity contained an expansile, multiloculated mass that displaced the lungs dorsocaudally. The mass, within the pericardial sac, compressed adjacent myocardium. Cut surface revealed variably sized, fluid-filled spaces with multiple foci of hemorrhage and necrosis. Histologically, the mass was composed of solid foci of polygonal cells admixed with colloid-containing follicles. Immunohistochemical staining for thyroglobulin was positive, and staining for calcitonin was negative. Grossly, thyroid glands were normal, and serum thyroxine was within reference intervals.