The article covers two clinical cases of domestic cats suffering from a mediastinal form of lymphoma and provides their cytological, immunohistochemical, and pathohistological verification. The lymphoma immunophenotyping method using the B-cell markers CD79a and CD3 was used to identify T-cells. The mediastinal type of lymphoma in cats is usually rarely registered and statistically, the number of cases does not exceed 20%, which is consistent with our observations. Shortness of breath, difficulty with swallowing, lack of appetite, cyanotic mucous membranes, lymphadenomegaly of the mediastinal lymph nodes and effusion in the chest cavity were found in the clinically ill cats. An X-ray examination of the chest cavity revealed an increased contrast in the mediastinal area and displacement of the lungs towards the spine. A complete blood count revealed lymphopenia. Cytological smears of the chest cavity transudates revealed mostly monomorphic lymphoblasts with large rounded hyperchromic nuclei and narrow cytoplasm stained in light blue. The karyoplasm was somewhat granular, the nucleoli were visible, and the mitoses were atypical and numerous. The cytological picture in biopsy samples of mediastinal lymph nodes was characterized by a monomorphic population of lymphoblasts with an eccentrically located nucleus and moderately basophilic karyoplasm. The cell cytoplasm was vacuolated in some places, with presence of atypical mitotic figures. Most of the cells had two nuclei. Diffuse tumoral lesions of the chest cavity tissues, focal tumorous lesions of the lung parenchyma, and lymphadenopathy of the mediastinal lymph nodes were found during the autopsy in the first case. The second clinical case demonstrated the massive lymphadenopathy of the mediastinal lymph nodes. Histologically, a diffuse lesion by a monomorphic population of lymphoblasts was revealed in preparations from the soft tissues of the chest wall. The lymphoblasts’ insignificant cytoplasm, with nuclei from round to elliptical shape, infiltrated the chest wall’s soft tissues. It was found immunohistochemically that the blast cells showed reactivity to CD79a, and were mostly negative to CD3. This indicates the development of a large diffuse B-cell lymphoma. The immunohistochemical picture of lymph node necropsies from another cat was somewhat similar. However, it was also characterized by lymphoblasts with eccentrically placed nuclei, increased number of cells with mitotic figures, somewhat intensive CD3 antibodies expression (especially in the paracortical area of lymph nodes), and significant CD79a marker expression.

Lymphoma is one of the most common neoplasias in cats, affecting various organs and tissues. Extranodal lymphoma is characterized by local damage to such organs as the nose, eyes, skin, central nervous system, and kidneys. Cats usually have bilateral kidney damage with possible metastatic damage to the liver and lungs. Statistically, the extranodal type of lymphoma, namely the renal form, is found in 7% to 30% of cases, mainly in cats older than five years. Clinical signs of renal lymphoma are non-specific and variable, typical for acute renal failure, and manifest themselves through general exhaustion, polyuria, polydipsia, and renomegaly. In most cases, the prognosis for lymphoma in cats is cautious. The article describes two clinical cases of outbred cats with a primary renal form of lymphoma. In both cases, the cats were clinically diagnosed with acute kidney injury and treated symptomatically. An ultrasound examination of the cats’ kidneys revealed a sharp increase in their volume and increased echogenicity of the cortical layer with a fine-grained and nodular structure. The cytological picture in fine-needle aspirates from the kidneys was characterized by a massive monomorphic population of lymphoblasts, which exceeded erythrocytes by 2–3 times in diameter. The cytoplasm of the lymphoblastic cells was sparse with large round nuclei with dense chromatin. The cells were mostly uninucleate, with atypical mitoses and moderate cellular atypism. Epithelial cells, which were occasionally visualized between large lymphoblastic cells, had broad vacuolated cytoplasm and a large round nucleus. Express tests for feline leukemia virus showed negative results. Both cats died 7 and 10 days after initiation of treatment, respectively. During the autopsy, sharply enlarged and deformed kidneys were recorded, and the border between the cortical and medullary substances was difficult to differentiate. Irregularly shaped, white tumorous formations were visualized in the cortical layer. Diffuse infiltration of the kidneys’ cortical layer with large monomorphic lymphoblastic elements with large hyperchromic nuclei and narrow cytoplasm was noted histologically. Lymphoblastic cells in a state of vacuolar and hydropic dystrophy were located between the proximal and distal tubules. The lumens were filled with protein mass and desquamated epithelium. The capsule of the kidney glomeruli was slightly thickened and the vessel walls were soaked with plasma proteins. Immunohistochemically, intensive expression of the CD79a marker and high expression of the Ki-67 marker were detected in the examined kidney samples, which indicates the development of diffuse B-cell lymphoma with an unfavourable prognosis.