An immunohistochemical investigation of 18 cases of feline nasal lymphoma.

This report details clinical, histopathological and immunohistochemical findings in 18 cats with chronic nasal disease diagnosed as nasal lymphoma. Eight of the cats were female and 10 were male, with a median age of 10.5 years (range 7-14 years). Three of the cats were Siamese, one was Burmese, and the rest were non-pedigree. The duration of clinical signs before referral ranged from 30 to 540 days (median 88.5 days). The most common clinical signs were nasal discharge, stertor and sneezing. Nasal radiographs were abnormal in 14/16 cases examined. Abnormal masses were detected endoscopically in 13/18 cases. Nine cats received multi-agent chemotherapy or radiation therapy, or both, with survival times ranging from 14 to >541 days. Biopsy material from these 18 cats was examined by light microscopy, and serial sections were subjected to immunohistochemical labelling for the T lymphocyte marker CD3 and the B lymphocyte marker CD79a. In 13 tissues, expression of class II molecules of the major histocompatibility complex and the myelomonocytic antigen MAC387 was also determined. Twelve of the tumours were classified as diffuse large B-cell lymphomas, four as lymphoblastic B-cell lymphomas, and one as a follicular B-cell lymphoma. The tumour cells within these lesions all expressed CD79a, and (where tested) most also expressed MHC class II. One tumour was an anaplastic large cell neoplasm, in which the neoplastic cells expressed MHC class II alone in the absence of either lymphoid marker. There was a variable infiltration of reactive small T lymphocytes into these tumours, and zones of necrosis within the tumour tissue were sometimes heavily infiltrated by MAC387+ phagocytic cells.