Radiation can “Take a Bite out of Oral Tumors”

Oral tumors are often devastating for our patients. For an animal having any tumor is not easy…but when that tumor is in the mouth it also can also cause major problems such as pain, difficulty eating or swallowing food, bleeding, infection, and an overall decrease in quality of life. Oral tumors are best treated with surgical excision, as this can fix the local problem quickly. However, many times oral tumors can not be treated with surgery or surgery can not completely remove the tumor. In these cases, radiation therapy is often very useful in controlling tumors and improving quality of life. Here are the top five oral tumors in pets where radiation can really make a difference:

Melanoma
Radiation therapy can be very effective in the treatment of melanomas in dogs. The good news concerning melanoma and radiation is that hypofractionated radiation seems to be very effective. This involves using a small number of treatments (3 to 6) with a larger dose for each treatment (5 to 10 Gy). This means less visits, fewer anesthetic episodes, minimal side effects and less cost to the owners. Two main published studies have shown that dogs with gross tumor have overall response rates in 85-95% of cases with a complete response in 50 -75% of dogs. Side effects of this type of radiation are minimal (Bateman, JVIM 1994 and Blackwood, JAVMA 1996)

Figure 1 Aggressive oral melanomas can respond well to a few radiation treatments.
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Soft tissue sarcomas

The second most common oral tumor in dogs is oral fibrosarcoma. Also dogs can develop other soft tissue sarcomas in the mouth that can be very difficult to handle. Aggressive surgery is usually the treatment of choice. However, for cases where surgery is not possible, or the mass is incompletely removed, radiation can be beneficial. In one study treatment of sarcomas after an incomplete excision resulted in a survival time of 540 days (Forrest, JVIM 2000). For tumors that were not able to be surgically excised, in another study, oral sarcomas were controlled for 11 months with definitive radiation and 6 months with palliative radiation. Another interesting facet about this study is that dogs treated with palliative radiation lived almost as long (10months) as dogs treated with definitive radiation (11months) (Poirier, In Vivo 2006)

Figure 2 Treatment of canine oral sarcomas with radiation can result in tumor control for 6 to 11 months. These images show pre and post treatment images for a dog in a complete remission one year after palliative radiation for a fibrosarcoma.

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Acanthomatous Epulides

These tumors are uncommon in dogs. Typically, they are locally invasive, but they can be cured with an aggressive, complete surgical removal. However, in cases where surgery is not an option, radiation can also be very effective. In one study dogs treated with radiation had an overall survival of over 3 years, with many dogs living even longer. (McEntee, Vet Radiol Ultrasound 2004)

Figure 3 Acanthomatous epulides can be controlled long term with radiation alone.

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Oral Lymphoma

Although it is relatively rare, some dogs will develop a localized lymphoma, involving just the oral mucosa. While we typically think of chemotherapy first for lymphoma, this tumor seems to respond best to treatment with radiation to the oral cavity. In the best study looking at this to date 1/3 of dogs responded to radiation with a median survival of over 2 years (Berlato, Vet Comp Oncol 2012)

Oral Tumors in Cats

Unfortunately oral tumors in cats are most commonly squamous cell carcinomas. A number of studies using various accelerated radiation protocols have shown responses and prolonged survival. Unfortunately, these responses re usually short lived and survival for cats with oral squamous cell carcinomas is typically 2-6 months on average (Poirier, Vet Radiol Ultrasound 2013 and Fidel, Vet Radiol Ultraosund 2007).
However, palliative radiation may help control pain and improve quality of life in some cats (Sabhlok, Vet Radiol Ultrasound 2014)

Radiation can also be used to treat other tumor such as sarcomas or melanomas in cats. However, given how uncommon these tumors are there are limited studies describing treatment (Farrelly, Vet Radiol Ultrasound 2004)

John Farrelly, DVM, MS , ACVIM (Oncology), ACVR (Radiation Oncology)

References

Blackwood L, Dobson JM. Radiotherapy of oral malignant melanomas in dogs. J Am Vet Med Assoc. 1996 Jul 1;209(1):98-102.

0-7-21 radiation therapy for the treatment of canine oral melanoma.

Bateman KE, Catton PA, Pennock PW, Kruth SA.

J Vet Intern Med. 1994 Jul-Aug;8(4):267-72.

Forrest LJ, Chun R, Adams WM, Cooley AJ, Vail DM. Postoperative radiotherapy for canine soft tissue sarcoma. J Vet Intern Med. 2000 Nov-Dec;14(6):578-82.

Poirier VJ, Bley CR, Roos M, Kaser-Hotz B. Efficacy of radiation therapy for the treatment of macroscopic canine oral soft tissue sarcoma. In Vivo. 2006 May-Jun;20(3):415-9.

McEntee MC, Page RL, Théon A, Erb HN, Thrall DE. Malignant tumor formation in dogs previously irradiated for acanthomatous epulis.

Vet Radiol Ultrasound. 2004 Jul-Aug;45(4):357-61

Berlato D, Schrempp D, Van Den Steen N, Murphy S. Radiotherapy in the management of localized mucocutaneous oral lymphoma in dogs: 14 cases. Vet Comp Oncol. 2012 Mar;10(1):16-23.

Sabhlok A, Ayl R. Palliative radiation therapy outcomes for cats with oral squamous cell carcinoma (1999-2005). Vet Radiol Ultrasound. 2014 Sep-Oct;55(5):565-70.

Poirier VJ, Kaser-Hotz B, Vail DM, Straw RC. Efficacy and toxicity of an accelerated hypofractionated radiation therapy protocol in cats with oral squamous cell carcinoma. Vet Radiol Ultrasound. 2013 Jan-Feb;54(1):81-8.

Fidel JL, Sellon RK, Houston RK, Wheeler BA. A nine-day accelerated radiation protocol for feline squamous cell carcinoma. Vet Radiol Ultrasound. 2007

Farrelly J, Denman DL, Hohenhaus AE, Patnaik AK, Bergman PJ. Hypofractionated radiation therapy of oral melanoma in five cats.

Vet Radiol Ultrasound. 2004

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