Evaluation of an Accelerated Chemoradiotherapy Protocol for Oropharyngeal Squamous Cell Carcinoma in 5 Cats and 3 Dogs

Abstract

Accelerated radiation therapy protocols address the specific biology of aggressive oropharyngeal squamous cell carcinoma and this approach was applied in 5 feline and 3 canine oropharyngeal squamous cell carcinoma patients where surgery was not possible (4/5 feline and 2/3 canine cases) or was declined (1/5 feline and 1/3 canine cases). A protocol using 14 fractions of 3.5 Gy over 9-days, combined with carboplatin chemotherapy as a radiosensitiser (total dose 180 mg/m2 in feline and 300 mg/m2 in canine cases) resulted in a complete tumor response in most cases (4/5 feline and 3/3 canine cases) with acceptable acute and long-term side effects. Results achieved in feline cases correspond with published data where these specific radiotherapy protocols were employed. A complete response and long-term survival (> 2-years) was achieved in all canine patients. Although no standardized chemoradiotherapy protocols currently exist, this therapeutic approach can be a useful addition for the management of oropharyngeal squamous cell carcinoma of cats and dogs when the goals of treatment include maximizing tumor control while maintaining function and quality of life.

Histopathologic Diagnoses From Biopsies of the Oral Cavity in 403 Dogs and 73 Cats

“…26 A recent study of 5 cats and 3 dogs with oral SCC that were treated with carboplatin as a radiosensitizing agent and an accelerated protocol demonstrated promising results. 22…”

“…20,21 The accelerated protocol delivers the total treatment in a shorter period of time and sometimes in a larger number of fractions (hyperfractionation). 22 Accelerated protocols have proven beneficial for local control of advanced head and neck SCC in humans. [23][24][25] The addition of a chemotherapeutic agent that causes the increased radiosensitivity of neoplastic cells has also been demonstrated to be beneficial.…”

“…26 A recent study of 5 cats and 3 dogs with oral SCC that were treated with carboplatin as a radiosensitizing agent and an accelerated protocol demonstrated promising results. 22 Curative intent excisional surgery followed by RT 2 weeks later currently yields the best results in treating feline oral SCC. One study reported that 85% of cats (6 of 7) had a median recurrence time of 12.5 months.…”

Long-term survival in a cat with tonsillar squamous cell carcinoma treated with surgery and chemotherapy

“…Carboplatin has been used in both dogs and cats with various SCCs of the oral cavity, specifically as a radiosensitiser. 4,[6][7][8][9][10] A phase 1 clinical trial in cats concluded that carboplatin could be administered at a maximum tolerated dose of 240 mg/m 2 IV; 17 in our case, although only a grade II GI and haematological toxicity was shown, a dose reduction was made due to owner's concerns and subsequent treatments were reported to be well tolerated since. Despite instituting adjuvant treatment, local recurrence developed, suggesting chemotherapy may not have any efficacy in controlling the disease locally.…”

“…3,4 Treatment options include surgery, radiotherapy (RT) alone or in association with chemotherapy, and tyrosine kinase inhibitors (TKIs). 1,2,[5][6][7] A retrospective study evaluating 31 cats with oral SCCs (located in the tongue, mandible, maxilla, tonsil and cheek) without distant metastases treated with RT and carboplatin as a radiosensitiser reported a median survival time (MST) of 163 days (range 53-770 days). In this study, four cats with tonsillar SCCs, of which two underwent lymphadenectomy to treat local metastatic disease, were grouped together with one case of SCC involving the oral mucosa: MST was not reached, and cats were still alive at the time of study closure, with a mean survival of 724 days, which was significantly longer when compared to the outcome of those patients with tumours in other anatomical locations (cats with SCCs of the tongue, mandible and maxilla experienced an MST of 141 days).…”