Diagnosis of canine renal lymphoma by cytology and flow cytometry of the urine

Lymphoma is a common hematopoietic neoplasm of dogs. A definitive diagnosis typically requires the collection of samples via fine‐needle aspirate or biopsy. A unique case of canine renal T‐cell lymphoma diagnosed using urine sediment microscopy with flow cytometry and PCR for Antigen Receptor Rearrangement (PARR) is presented. A fresh urine sample was collected via a urinary catheter and immediately prepared for cytologic examination, flow cytometry, and PARR. The flow cytometric study revealed that 83% of the cells were large CD3+CD8+ T cells, while PARR identified a clonally rearranged T‐cell receptor gene, supporting the flow cytometry findings. Despite supportive care, the patient progressed to anuric renal failure and was humanely euthanized. A necropsy was performed, and tissues from the upper and lower urinary tracts were collected. Histologically, the right and left kidneys were infiltrated by a neoplastic round cell population effacing the cortex and medulla. Immunohistochemistry for the T‐ and B‐cell antigens CD3 and CD20, respectively, revealed that the neoplastic population within the kidney demonstrated diffuse, strong, membranous to intracytoplasmic CD3 expression while lacking CD20 expression. These results confirmed the diagnosis of renal T‐cell lymphoma. This is the first known report of canine lymphoma diagnosed using either urine flow cytometry or clonality testing. Therefore, in select cases, urine flow cytometry and/or PARR are feasible to perform on urine‐derived cells as a quick and cost‐effective means to aid in the diagnosis of urinary tract lymphoma.