Yoshikawa H, Gieger TL, Saba CF, et al. Retrospective evaluation of intranasal carcinomas in cats treated with external‐beam radiotherapy: 42 cases. J Vet Intern Med. March 2021: jvim.16098. doi:10.1111/jvim.1609
Nasal tumors commonly occur in cats and are often slow growing, causing slowly progressive upper respiratory signs before leading to life threatening disease. While lymphoma is a common nasal tumor in cats, carcinomas also occur frequently (termed intranasal carcinoma; INC). Due to the complex regional anatomy of the nasal cavity and the locally invasive nature of the tumors, nasal carcinomas are not generally amenable to surgical excision. Chemotherapy is also generally of little efficacy; as such radiation therapy is commonly used. Much of the data on the efficacy of radiation therapy for INC in cats is based on older radiation technologies. Newer modalities, including stereotactic and intensity-modulated radiation therapy, are now available that have led to improved prognoses and less side effects in a wide variety of cancers.
The goal of this study was to investigate the clinical outcome in cats with INC treated with palliative and definitive intent radiation protocols, and to determine factors that may predict outcome. It was designed as a retrospective observational study reviewing medical records at 7 veterinary referral hospitals. Cats with a cytologic or histologic diagnosis of INC treated with external beam radiation were enrolled in the study. Cats were excluded if there was surgical debulking, a lack of follow-up, or lack of details on the radiation protocol.
Definitive full course radiation therapy (FRT) was defined as at least 40Gy given in >10 fractions. Definitive intent stereotactic radiation (SRT) was defined as a minimum fractional dose of 8Gy and intrafraction interval of no greater than 2 days. Palliative radiation therapy (PRT) was defined as radiation therapy that was not FRT or SRT.
Kaplan-Meier analysis was used as the primary statistical method. Overall survival time (OST) was defined as the time from the start of radiation to death of any case, while progression free survival (PST) was time from start of radiation until clinical worsening of disease.
Forty two cats met enrollment criteria (24 male and 18 female) with a median age of 13.3 years. Diagnosis was based on histology in 33 cats and cytology in 9. All but one cat underwent a CT scan. Eighteen cats underwent SRT, 8 underwent FRT, and 16 underwent PRT. Regional lymph nodes were included in 8 cats.
Five cats did not complete the first course of radiation therapy. In the two that underwent post mortem examination, tumor growth was not considered the cause for decline. Thirty five cats underwent one course of radiation therapy, and 7 underwent a second course when tumor progression occurred after initial therapy.
The median OST was 591 days, with a 1-year survival of 60%, and 2 year survival of 29%. Progression free survival was 459 days, with 1- and 2-year progression free rates 52% and 0%. Cats undergoing definitive intent therapy had a median progression free survival of 504 days and overall survival of 721 days, compared with cats undergoing palliative intent therapy who had a progression free survival of 198 days and overall survival of 284 days. Cats who underwent a second course if relapse occurred lived a median of 824 days.
Nine cats had signs of acute radiation toxicity: three had alopecia, one had transient coughing, and five had oral mucositis. Two also experienced low grade ocular toxicosis. Late toxicities were uncommon and mild.
The authors conclude that radiation therapy for cats with nasal adenocarcinoma is safe, generally well tolerated, and effective. Survival rates are superior for animals treated with definitive vs palliative radiation.
Limitations to this study include its retrospective nature and the wide variety of treatment protocols used, which limited the ability to compare protocols. There were also a range of various concurrent therapies used including NSAIDs and corticosteroids. The sample size was relatively small, which may have limited the yield.
Overall, this study suggests that radiation therapy is associated with a good response rate, possibility of prolonged survival, and minimal toxicity in cats with nasal adenocarcinoma.
1. Mellanby RJ, Herrtage ME, Dobson JM. Long-term outcome of eight cats with non-lymphoproliferative nasal tumours treated by megavoltage radiotherapy. J Feline Med Surg. 2002;4:77-81.2.
2. Théon AP, Peaston AE, Madewell BR, Dungworth DL. Irradiation of nonlymphoproliferative neoplasms of the nasal cavity and paranasal sinuses in 16 cats. J Am Vet Med Assoc. 1994;204:78-83.3.
3. Straw RC, Withrow SJ, Gillette EL, McChesney A. Use of radiotherapy for the treatment of intranasal tumors in cats: six cases (1980-1985). J Am Vet Med Assoc. 1986;189:927-929.