EXPRESS: Large cell lymphoma in four cats after successful treatment of feline infectious peritonitis with oral GS-441524 - a novel clinical observation.
Buchta K, Meunier SM, Felten S, Erber K, Kipar A, Dorsch R, Zuzzi-Krebitz AM, Zwicklbauer K, Bergmann M, Matiasek K, Wenk J, De Witt Curtius CC, Spiri AMM, Meli ML, Cerchiaro I, von Both U, Unterer S, Hofmann-Lehmann R, Hartmann K · Journal of Feline Medicine and Surgery · 10 March 2026
Large cell lymphoma develops in 2% of cats post-FIP GS-441524 treatment; consider long-term monitoring.
This case series reports four cats that developed large cell lymphoma (LCL) within two years following successful feline infectious peritonitis (FIP) treatment with oral GS-441524. Among a cohort of 202 treated cats, four (2.0%) subsequently developed LCL at 81, 365, 365, and 595 days post-FIP diagnosis. Clinical presentations included weight loss, hyporexia, and chronic vomiting across all cases. Histological or cytological confirmation was obtained in all cases, with two cats demonstrating monoclonal B cell populations via antigen receptor rearrangement PCR. All affected cats were FeLV and FIV negative, and no persistent FCoV viral load or antigen was detected. Median survival after LCL diagnosis was 15.5 days. The 2.0% incidence substantially exceeds that reported in the general feline population, suggesting LCL may represent a delayed immunological complication or "long-FIP syndrome" following GS-441524 treatment. The pathogenic mechanism underlying this association remains unclear and warrants further investigation.
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