CD5+/CD21-Chronic Lymphocytic Leukemia in a Cat

Feline chronic lymphocytic leukemia (CLL) is a rare disease. Its diagnosis is not simple because of the absence of clinical signs and the presence of mature lymphocytosis. An 11-year-old female spayed Russian Blue cat was referred to the veterinary medical teaching hospital for lethargy, diarrhea, weight loss, and inappetence. Marked lymphocytic leukocytosis and a significantly increased number of small-to-intermediate-sized lymphocytes in the peripheral blood were found on hematological examination. The results of the feline leukemia virus and immunodeficiency virus test were negative. Further, mild splenomegaly was detected. Bone marrow aspirate analysis revealed mature lymphocytosis and a clonally rearranged T cell receptor gene with the polymerase chain reaction (PCR) for antigen receptor rearrangement assay. Flow cytometric immunophenotyping showed a homogeneous population of CD5+/CD21-T-cells in the peripheral blood and bone marrow. According to the results of the aforementioned examinations, CLL was diagnosed. Treatment was not initiated at the time of diagnosis because the clinical signs were mild and did not affect the quality of life. This report describes the clinical findings and use of advanced diagnostic tools such as molecular clonality analysis and immunophenotyping for the diagnosis of feline CLL.