Background: Recombinant feline interferon‐ω (rFeIFN‐ω) was tested as a treatment option for cats with fibrosarcoma to assess safety and feasibility. Hypothesis: Treatment with rFeIFN‐ω in cats with fibrosarcoma is safe and feasible. Animals: Twenty domestic cats. Methods: In an open‐labeled uncontrolled clinical trial 12 injections of 1 × 10(6) U/kg rFeIFN‐ω were administered over a 5‐week period: the 1st through 4th injections were given intratumorally, and the 5th through 12th injections were administered subcutaneously at the tumor excision site. Wide surgical excision of the tumors was carried out after the 4th injection and before the 5th injection of rFeIFN‐ω. A Common Terminology Criteria for Adverse Events (CTCAE) analysis was conducted. Flow cytometry of fibrosarcoma cells after incubation with rFeIFN‐ω and recombinant feline interferon‐γ was performed to assess the biological effect of rFeIFN‐ω. Results: Changes in blood cell count, increases in serum aspartate‐amino‐transferase activity, serum bilirubin concentration, serum creatinine and serum electrolyte concentrations, weight loss, anorexia, increased body temperature, and reduced general condition were observed but were mostly minor (grade 1 and 2) and self limiting. Eosinophilia (P= .025), neutropenia (P= .021), and weight loss (P < .001) were statistically correlated with rFeIFN‐ω‐treatment (analysis of parameters before treatment and after 3 injections of rFeIFN‐ω). Flow cytometry of 5 unrelated feline fibrosarcoma cell lines showed increased expression of major histocompatibility complex (MHC) class I molecules (P= .026) in response to in vitro incubation with rFeIFN‐ω, whereas expression of MHC class II molecules was not affected significantly. Conclusions and Clinical Importance: RFeIFN‐ω for the treatment of feline fibrosarcoma is safe, well tolerated, and can be easily performed in practice. To assess the efficacy of the treatment, it should be tested in a placebo‐controlled trial.
Adjuvant Immunotherapy of Feline Fibrosarcoma with Recombinant Feline Interferon‐ω