Retrospective evaluation of intranasal carcinomas in cats treated with external‐beam radiotherapy: 42 cases

Abstract

Background: Little is known regarding the comparative efficacy of various irradiation strategies used to treat intranasal carcinomas (INC) in cats. Objectives: Investigate outcomes and prognostic factors associated with survival for cats with INC. Animals: Forty-two cats with INC that underwent radiotherapy (RT). Methods: Single-arm retrospective study. Medical record review for cats with INC that underwent RT at 1 of 7 veterinary RT facilities. Irradiation protocols categorized as: definitive-intent fractionated RT (FRT), definitive-intent stereotactic RT (SRT), and palliative-intent RT (PRT). Median overall survival time (OST) and disease progression-free survival (PFS; documented by advanced transverse imaging, or recurrence of symptoms) were calculated. Associations between tumor stage, RT protocol/ intent, and adjunctive treatment usage and outcome were calculated. Results: Cats underwent SRT (N = 18), FRT (N = 8), and PRT (N = 16). In multivariate modeling, cats received definitive-intent treatment (DRT; FRT/SRT) had significantly longer median PFS (504 days, [95% confidence interval (CI): 428-580 days] vs PRT 198 days [95% CI: 62-334 days]; p = 0.006) and median OST [721 days (95% CI: 527-915 days) vs 284 days (95% CI: 0-570 days); p = 0.001]). Cats that underwent second DRT course at time of recurrence lived significantly longer than cats that received 1 RT course (either DRT or PRT [median OST 824 days (95% CI: 237-1410 days) vs 434 days (95% CI: 277-591 days); p = .028]). Conclusion: In cats with INC, DRT is associated with prolonged OST and PFS as compared to PRT. If tumor progression occurs, a second course of DRT should be considered.

Use of a cyclical hypofractionated radiotherapy regime (‘QUAD shot’) for the treatment of feline sinonasal carcinomas

“…8 In this study, many of the patients in the palliative group received only a small total dose (most cats had 32 Gy or less) or had advanced clinical stage disease. 8 More specifically, the survival time of cats receiving palliative-intent (hypofractionated) protocols was 284 days, compared with 721 days in the definitive-intent (fractionated/SRT) group. 8 Furthermore, in other studies of cats receiving hypofractionated protocols, the survival times range from 342 to 450 days, which is similar to the survival in the present study.…”

“…Toxicity may also have been under-reported as some of the follow-up examinations were performed at primary care clinics and not the hospital where the treatment was delivered, overall, though the late toxicity was reported to be low or of cosmetic importance (such as alopecia and leukotrichia) in previous studies. 7,8 VRTOG criteria were only partially applied, owing to the difficulty in retrospectively categorising the toxicity, as it was not always clearly recorded in the medical records. Post-mortem examination was not performed in any of the cases, therefore it is likely that some cats with progressive nasal signs had rhinitis due to late toxicity, rather than tumour progression.…”

“…4–8 Common hypofractionated protocols in sinonasal carcinomas in cats include doses of 16–36 Gray (Gy), 4,5,7,8 while finely fractionated protocols aim for a dose of at least 40 Gy given in ⩾10 fractions. 6,8…”

“…14 While the cyclical protocol is considered a palliative-intent option in human medicine, a high total dose of radiation therapy is given, which is similar to other finely fractionated protocols used in veterinary medicine. 6,8 To the best of the authors' knowledge, the use of such a cyclical hypofractionated protocol has not been reported in the veterinary literature. The aim of our study was to determine the tolerability, efficacy and outcome for cats with sinonasal carcinoma treated with this protocol.…”

“…14 While the cyclical protocol is considered a palliative-intent option in human medicine, a high total dose of radiation therapy is given, which is similar to other finely fractionated protocols used in veterinary medicine. 6,8…”