Oral squamous cell carcinoma in cats - treatment with radiotherapy

Tumors of the oral cavity represent approximately 10% of all tumors with squamous cell carcinoma (SCC) being one of the most frequently diagnosed oral malignant tumors.  Although oral SCC usually affects older cats it can develop at any age. Oral squamous carcinogenesis is a multistep process in which multiple genetic events occur and is still not completely understood. Risk factors in development of feline oral SCC may include the usea of flea collars, consumption of canned food (e.g. tuna) and exposure to environmental tobacco smoke. SCC can develop elsewhere in the oral cavity with sites of involvement including the gingiva, tongue, sublingual region, tonsils, oral mucosa, lip and palate.

An example of oral squamous cell caricinoma affecting rostral mandible (left) and an example of lingual squamous cell carcinoma in a cat (right).

The most common clinical signs associated with this malignant tumor include halitosis, salivation and anorexia. Squamous cell carcinoma typically occurs as ulcerative or proliferative lesion or mass which may bleed very easily. If oral SCC is developing in the proximity of maxillary, incisive or mandibular bone cats will present with clinical finding of loose tooth / teeth that became mobile due to the ability of a tumor to invade the underlying bone. Diagnostic approach to a cat with oral mass includes a thorough clinical examination with blood testing, diagnostic imaging (dental radiography and/or CT) and biopsy of the affected site for the histopathological confirmation of the squamous cell carinoma.

Squamous cell carcinoma affecting rostral mandible (left).  Dental radiography showing evidence of bone invasion, primarily osteolysis (right).

CT diagnostics and 3D reconstruction of the skull of a cat with maxillary squamous cell  carcinoma arising from the gingiva indicating involvement of the underlying bone.

Contrast CT diagnostics indicating enlargement of mandibular and medial retropharynegal lymph nodes in a cat with maxillary SCC.

CT diagnostics of the lungs indicating no signs of distant metastatic disease.

Feline oropharyngeal SCC remains a therapeutic challenge indicating local disease control as goal of therapy. Given the advanced stage of the disease at the time of the diagnosis in most feline patients, local surgical excision is usually not considered curative intent treatment. Chemotherapy is not effective in the treatment of oral SCC. Conventional radiation therapy protocols alone are not able to control feline oropharyngeal SCC possibly due to its very specific tumor biology. Squamous cell carcinoma tumor cells have a very rapid tumor doubling time of only few days.

Accelerated radiotherapy protocols have been developed to combat rapid tumor repopulation by dividing the total radiation dose into multiple small doses that are delivered at shorter intervals providing better tumor control. With accelerated radiotherapy protocols we finish the treatment in 9 or 10 days. Although no standardised radiotherapy protocols currently exist, this therapeutic approach can be a useful addition for the management of oropharyngeal SCC of cats when the goals of the treatment include maximising tumor control while maintaining function and quality of life.


An example of the tretment of mandibular SCC in a cat with radiotherapy. Left upper picture: oral SCC before treatment. Right upper picture showing regression of the lesion after finished radiotherapy treatment. Lower picture showing a complete response 3 months after finished radiotherapy treatment.

An example of the treatment of lingual SCC in a cat radiotherapy. Left upper picture indicating lingual SCC before treatment. Right upper picture showing regression of the lesion after finished radiotherapy treatment. Left lower picture showing further regression of the lesion 3 weeks after finished radiotherapy treatment. Right lower picture showing a complete response 2 years after finished radiotherapy treatment.

An example of the treatment of maxillary SCC in a cat radiotherapy. Left picture indicating maxillary SCC before treatment. Middle picture showing regression of the lesion after finished radiotherapy treatment. Right picture showing a complete response 2 years after finished radiotherapy treatment.

 

REFERENCES:

A Rejec et al., 2015. Evaluation of an Accelerated Chemoradiotherapy Protocol for Oropharyngeal Squamous Cell Carcinoma in 5 Cats and 3 Dogs. J Vet Dent 2015; 32(4):212-21. 

MC McEntee (2012). Clinical behavior of nonodontogenic tumors. In: Verstraete FJM, Lommer JM, eds. Oral and maxillofacial surgery in dogs and cats. Edinburgh, Saunders Elsevier, pp. 387-392.

G Romanelli and JR Lewis (2018). Management of oral and maxillofacial neoplasia. In: BSAVA manual of Canine and Feline Dentistry and Oral Surgery. British Small Animal Veterinary Association, pp. 279-293.

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