Abstract
Background:
Feline nasal epithelial tumors are locally invasive and radiosensitive, and radiotherapy is the standard treatment. However, recurrence is common, and the role of reirradiation in cats remains unclear.

Aim:
This retrospective study aimed to evaluate the efficacy and safety of hypofractionated reirradiation in cats with recurrent nasal epithelial tumors.

Methods:
The medical records of cats treated with hypofractionated radiotherapy for intranasal epithelial tumors at Azabu University Veterinary Teaching Hospital between 2014 and 2022 were reviewed. Follow-up continued until August 2023.

Results:
Twenty-six cats were treated, 11 of which underwent reirradiation after clinical progression. The median interval between treatments was 356 days. In the first course, responses included complete (n = 1), partial (n = 7), stable (n = 16), and progressive (n = 2) diseases. In the second course, all cats achieved stable disease. The median overall survival was significantly longer in the reirradiation group than in the nonreirradiation group (562 vs. 58 days, p <0.001). Although not statistically significant (p = 0.08), adenocarcinomas tended to have longer OS than squamous cell carcinomas. Acute adverse events (Veterinary Radiation Therapy Oncology Group grade 1–2), including conjunctivitis, alopecia, and dermatitis, were observed. Late adverse events, such as leukotrichia and hyperpigmentation, did not affect survival. Two cats developed grade 3 late toxicities (cutaneous or oral–cutaneous–nasal fistulas) associated with bone lysis and short inter-treatment intervals.

Conclusion:
Hypofractionated reirradiation may be a viable salvage option for feline nasal epithelial tumors, particularly in cases with adenocarcinoma or early-stage disease, with acceptable toxicity when patients are carefully selected.

Key words: Adverse event; Feline; Nasal tumor; Recurrence; Reirradiation.