Peripheral T-Cell Lymphoma in the Oral Cavity of a Cow

Background: Squamous cell carcinomas and lymphomas are the most prevalent neoplasms in cattle, the latter usually being attributed to infection by bovine leukemia virus (BLV). Neoplasms of the oral cavity are sporadic in cattle, with but a single case of lymphoma involving this anatomic site in a bovine reported to date. This paper reports a case of lymphoma involving the oral cavity of a dairy cow. The clinical and pathological aspects of the tumor are described and discussed. Case: A 39-month-old Holstein-Friesian cow was presented with weight loss and a tumorous growth in the left masseter region, tearing in the left eye, and mild ipsilateral exophthalmos. Treatment with antibiotics was unsuccessful. The tumor growth was 16 x 11 cm, with a soft center and firm periphery, multilobulated, with white intercalated with black and friable areas from which a fetid odor emanated. The cut surface was predominantly white-yellow. A cross-section of the head, caudal to the second molar, revealed a mass infiltrating and almost completely obliterating the left nasal cavity, destroying the frontal sinus, the ventral conchae, and the middle and ventral meatus, and compressing the common meatus. The tracheobronchial, mediastinal, and internal iliac lymph nodes were enlarged and masses with similar characteristics to those in the oral cavity replace their parenchyma. Microscopically, the mass consisted of large neoplastic lymphocytes arranged in a non-encapsulated and infiltrative mantle and supported by scarce fibrovascular tissue. The cytoplasm of neoplastic cells was scarce and had distinct boundaries; the nuclei were round or oval, the chromatin was finely granulated, and the prominent nucleolus had occasionally multiplied. Nuclear pleomorphism was marked and there were, on average, five mitotic figures per microscopic field of 400x. Similar neoplastic cells obliterated the normal structure of the tracheobronchial, mediastinal, and internal iliac lymph nodes. In the immunohistochemical examination, labeling was diffuse and moderate in the cytoplasm of neoplastic cells when a CD3 antibody was used, and negative when antibodies to CD79a, cytokeratin, and vimentin were used. Due to its characteristic markings in the immunohistochemistry panel, the neoplasm was classified as an unspecified peripheral T-cell lymphoma. Discussion: The diagnosis of lymphoma was based on clinical signs and gross and histopathological findings, and was confirmed by immunohistochemistry. Lymphomas in cattle are common in several organs as part of enzootic bovine leukosis, a virus-induced type of B-cell lymphoma. However, lymphomas are rare in the oral cavity. The clinical presentation observed in this case points to the upper alimentary tract as the primary site of the neoplasm once clinical respiratory signs were not observed in the cow. The neoplasm cells described here presented a T-cell profile in immunohistochemistry panel, suggesting that the tumor should be included in the sporadic form of bovine leukosis since B-cells are the cellular population in cases of enzootic bovine leukosis. However, since the diagnosis of enzootic leukosis was not definitively excluded in this case, the cause of the neoplasia cannot be conclusively determined. It is concluded that, although rare, lymphomas may indeed occur in the bovine oral cavity and should be included in the differentials list for tumoral growth in the lateral region of the bovine face.