Although the oral cavity may not be the most common location we think of when discussing cancer in companion animals, oral cancer represents a significant risk in both our canine and feline patients. Oral cancer accounts for 6-7% of all canine cancers and 3% of all feline cancers. Oropharyngeal cancers are 2.6 times more likely to be found in dogs than in cats.
Breeds that are reported to have a higher risk for developing oral tumors include: cocker spaniels, German shepherds, German shorthaired pointers, Weimaraners, golden retrievers, Gorden setters, miniature poodles, Chow chows and boxers. In dogs the most common malignant oral tumors include malignant melanoma, squamous cell carcinoma (SCC) and fibrosarcoma. Other tumors reported less commonly in the oral cavity of dogs include osteosarcoma, chondrosarcoma, multilobular osteochondrosarcoma, hemangiosarcoma, mast cell tumor, lymphoma and transmissible venereal tumor. We will discuss the three most common canine oral tumors in greater detail.
Malignant melanoma of the oral cavity represents 30-40% of all malignant, canine oral tumors. It is typically a very aggressive tumor. Not only does this tumor invade local oral tissues (often including bone), it also has a high propensity to metastasize to both the local lymph nodes and the lungs. As a result of its high metastatic potential, any patient diagnosed with a malignant melanoma should have sampling performed of the local lymph nodes as well as three-view thoracic radiographs and a minimum database (CBC/Serum Chemistry/UA). Despite its aggressive behavior, there are therapies that can slow disease progression and keep patients more comfortable.
Figure 1. Patient with amelanotic melanoma
Because of its aggressive behavior, both local and systemic treatment is recommended. Local treatment options consist of surgery and radiation therapy. Obtaining excellent local control with surgery and/or radiation therapy is vital. In many cases a CT scan may be helpful to determine the full extent of the tumor and help plan either surgical excision or radiation therapy. If the tumor can be completely excised, surgery is the preferred treatment method, but if the tumor is not excisable or the surgical margins are incomplete, radiation therapy is an excellent option to help control local disease. Radiation therapy is typically handled well by these patients and melanomas are very sensitive to radiation therapy, often resulting in good outcomes.
If we only work to control the local disease, we can expect to see metastatic disease within months of the initial diagnosis. Historically, melanoma has not responded well to chemotherapy. The addition of immunotherapy and specifically the Merial Melanoma Vaccine (Oncept) has been beneficial in treating this disease. Prior to the addition of the vaccine, the average survival time for patients with oral melanoma with surgery alone was less than 1 year. With the addition of the vaccine (with excellent local disease control) we are seeing patients live 1-3 years after diagnosis! The vaccine is typically handled well. Potential side effects include pain/inflammation at the injection site and very rare anaphylactic reactions.
Squamous cell carcinoma represents 17-25% of all malignant oral tumors in dogs, making it the second most common tumor found in the canine oral cavity. These tumors are locally aggressive, often invading bone. The metastatic rate is site dependent, with rostral SCCs having a low metastatic potential and tumors of the caudal tongue and tonsil having a high metastatic rate. As with any oral tumor, staging should include local lymph node palpation/aspiration, three-view thoracic radiographs, and a minimum database (CBC/Serum Chemistry/UA). Due to the high risk of bone involvement, a CT scan is recommended to determine the full extent of the tumor and help plan therapy. The treatment of choice for these tumors is surgery and/or radiation therapy. For tumors located in the rostral oral cavity complete surgical excision is more likely and with excellent local control the median survival time is 26-36 months. For caudally located tumors or tonsillar tumors, surgery and/or radiation therapy are still recommended, but given the higher propensity to metastasize, survival times are typically shorter and systemic therapy is often recommended. Piroxicam has been shown to benefit dogs with oral SCC and the benefit is even greater when combined with injectable carboplatin.
Fibrosarcoma is the third most common tumor found in the canine oral cavity representing 8-25% of oral tumors. The metastatic rate of these tumors is low; but they tend to be very aggressive locally, often invading bone. Despite the low metastatic potential staging with local lymph node palpation/aspiration, three view thoracic radiographs and a minimum database is recommended. The most common treatments employed for this tumor type include surgery and radiation therapy. Fibrosarcomas have a poor to fair response to radiation therapy, but when combined with surgical excision can result in good outcomes. With excellent local control the median survival time is 18-26 months.
Although oral tumors are more commonly found in dogs, they can be found in our feline patients as well.
Squamous cell carcinomas are the most common malignant oral tumor found in cats (70-80% of feline oral tumors are SCCs). These tumors are most commonly seen in middle aged to older cats. The metastatic rate is low, but they are very locally invasive causing pain and discomfort. Bone involvement is common. Treatment for these patients is aimed at slowing disease progression and decreasing pain and discomfort. Surgical response is poor with a median survival time of 45 days. Surgery combined with radiation therapy results in a slightly longer median survival of 90 days. In one study non-steroidal anti-inflammatory drugs were shown to benefit patients and slow disease progression. The oral tyrosine kinase inhibitor, Palladia may also be beneficial in slowing disease progression. Often a combination of radiation therapy, palladia, metacam and pain medications is beneficial at decreasing the pain that these cats experience as well as slowing disease progression. With this combination of treatments we may see survival times of 3-6 months. Any NSAID used in cats must be done cautiously with careful monitoring of renal values. The administration of analgesics is extremely important to maintain comfort in these patients. Buprenorphine is a common choice and is easy to administer even in cats with oral discomfort.
Fibrosarcomas are the second most common oral tumor found in the cat, comprising 13-17% of feline oral tumors. As with SCC this tumor has a low metastatic potential but is very locally aggressive, often involving bone. Again, the combination of surgery and radiation therapy offers the best outcome. A CT scan prior to initiating therapy is recommended due to the high potential for bone involvement. With excellent local control survival times of a year or more can be seen.
Oral tumors in both cats and dogs tend to be locally aggressive with a low to high potential for metastasis. However, there are many potential treatment options that can lead to a better quality of life for our patients. Tumor control and slowing disease progression is important. However, it is vital to remember that many of these tumors are painful and judicious use of analgesics is just as important as trying to control disease.
The Veterinary Cancer Center – November 2014
Bergman PJ, McKnight J, Novosad A, et al: Long-Term Survival of dogs with advancer malignant melanoma after DNA vaccination with xenogenic human tyrosinase: a phade I trial, Clin Cancer Res 9:1284; 2003.