Successful treatment and long-term follow-up of a young cat with feline infectious peritonitis and renal lymphoma

Background: Feline lymphoma is often a fatal disease, and achieving a cure with chemotherapy is questionable. Feline infectious peritonitis (FIP) diagnosis was historically associated with a poor prognosis and high mortality, but remission is possible with the newly available treatment. Long-term follow-up data on treated patients remain limited. Case description: A 3.9-year-old neutered male cat presented with hyporexia and lethargy lasting for several days. An abdominal mass was palpated on clinical examination and confirmed to be a renal mass on a computed tomography angiography scan. Ultrasound-guided fine needle aspirates and cytological evaluation revealed a large-cell renal lymphoma. A modified Cyclophosphamide, vincristine and prednisolone protocol with vinblastine addition (Cyclophosphamide, vincristine, prednisolone and vinblastine protocol) was started, resulting in a complete response. Twenty weeks after chemotherapy initiation, the cat developed anorexia, fever, and pleural effusion. FIP was diagnosed based on a positive reverse transcription polymerase chain reaction test from the pleural effusion. Subcutaneous administration of GS441524 led to FIP resolution. Conclusion: The cat did not receive any further treatment for both FIP and lymphoma. Still alive and well, almost 5 years after the diagnosis. To the author’s knowledge, this is the first case of renal lymphoma in a cat that subsequently developed FIP. Further studies on the potential correlation between lymphoma, chemotherapy, and FIP are needed. © 2025, Faculty of Veterinary Medicine, University of Tripoli. All rights reserved.