Get armed to the teeth about veterinary oral tumors
Is that oral mass gingival hyperplasia or a tumor? Should you just shave it off with a blade, or is a more extensive procedure indicated? What diagnostics should you run if you see an oral mass during a dental cleaning? In this article, CVC educator Laura D. Garrett, DVM, DACVIM (oncology), provides answers to these questions and more.
What are the most common neoplasms in the oral cavity?
In dogs, the most common tumor types in the mouth are squamous cell carcinoma (SCC), fibrosarcoma, melanoma and acanthomatous ameloblastoma (previously known as acanthomatous epulis).
SCC, fibrosarcoma and melanoma are all locally invasive but have different metastatic behavior, Dr. Garrett says. Almost all oral melanomas are malignant and highly metastatic. Oral fibrosarcoma very rarely metastasizes. Oral SCC varies in ability to metastasize—tonsillar SCCs frequently metastasize to locoregional lymph nodes, lingual SCCs have a lower rate of metastasis, and mandibular or maxillary SCCs are very unlikely to metastasize.
Acanthomatous ameloblastoma invades locally into bone, grows very slowly, tends to regrow if not completely excised, and can get quite large—but it doesn’t metastasize.
Dogs that present with oral tumors are generally middle-aged to older. Oral tumors in younger dogs are unusual and tend to have a high degree of malignancy. One exception is papillary SCC, which can be cured with excision or radiation.
What are the signs of oral neoplasia?
Signs of oral neoplasia can mimic the signs of dental disease. The owner may report bleeding from the mouth, blood in the water bowl, difficulty eating, tooth loss or halitosis. Oral neoplasia can also cause facial deformity.
Patients are often brought in for a routine dental prophylaxis, and the oral mass may be found during routine examination. According to Dr. Garrett, there is no pathognomonic appearance for each specific oral cancer.
How do you know whether it is a tumor or just gingival hyperplasia or a benign epulis?
There are several things to consider, says Dr. Garrett. Where is the mass located? If the mass is on both sides of the tooth (crosses the tooth line), it is likely a neoplastic process. What is the surface of the mass like? Benign epulides and gingival hyperplasia have a surface that resembles the rest of the gingival mucosa, while tumors may be ulcerated, colored differently, friable, etc. Are teeth loose or falling out? Neoplasia will cause this, while gingival hyperplasia or benign epulis will not.
Well, I think I have identified an oral tumor. Now what?
Time for diagnostics! If the patient allows, obtain a fine-needle aspirate of the mass. Dr. Garrett also recommends aspirating the regional lymph node (mandibular) and submitting it for cytology, even if it appears normal on palpation. She says SCC and fibrosarcoma metastasize to the local lymph node less than 10% of the time, while melanoma metastasizes more than 80% of the time, ultimately. The lymph node may provide a diagnosis (if tumor cells are present) as well as provide prognostic information. If cytologic examination of the mass and lymph node is nondiagnostic, an incisional biopsy of the mass is recommended to obtain a diagnosis before considering surgical excision. If pursuing surgical excision, Dr. Garrett says to make sure to note the location of the tumor in the mouth and to measure the mass before placing it in formalin (because it will shrink). Accurate staging and prognosis for some tumors (melanoma) depends on the size.
If the owner balks at the cost of diagnostics, advise them that prognosis and treatment depend on the results. Oral melanoma, which can look like anything, has a high rate of metastasis, and, according to Dr. Garrett, 40% of oral tumors are aggressive melanoma that invades bone and metastasizes to local lymph nodes and lungs early.
The results of a minimum database (complete blood count, serum chemistry profile, urinalysis) are usually unremarkable, unless other disease processes are present. Oral radiographs can be taken to look for bone lysis; be warned that 50% of bone must be destroyed to see evidence of lysis on a radiograph. Computed tomography (CT) scans are the preferred modality to assess the extent of local disease.
There is no risk of metastasis with acanthomatous ameloblastoma, so a metastatic check is not required before treatment. For all other aggressive oral lesions, evaluation of the lungs with radiography or CT is recommended before planning definitive therapy.
Mandibulectomies, maxillectomies and glossectomies ... oh my! How do I counsel the owner?
While radical surgical excision of oral neoplasms can seem scary to clients, Dr. Garrett says that dogs and many cats do very well after surgery and have a great quality of life. Many surgeons are gifted not only in excising the cancer but also in obtaining good cosmesis.
Even without a tongue, dogs can learn to drink and eat meatballs. Yes, they must submerge their entire muzzles to slurp up water, and there is a learning curve, but most dogs get the hang of it quickly and are happy companions. Most importantly, surgery allows these dogs to be without pain. Dr. Garrett recommends putting in a feeding tube at the time of surgery to facilitate nutrition and medication administration while the patient is figuring out the new normal.
Oncologists will recommend combination therapy based on tumor type of tumor, size and location. Surgery is recommended for bulky disease, as is follow-up care with radiation or chemotherapy, depending on tumor type.
Dr. Garrett says SCC may respond to piroxicam, carboplatin and toceranib phosphate (Palladia—Zoetis). Bulky SCC may also respond to radiation, although surgery is the treatment of choice for most cases.
Melanoma can be treated with some combination of surgery, radiation and chemotherapy, says Dr. Garrett. The primary tumor can be surgically excised or treated with course fraction radiotherapy (e.g. one large dose once weekly for four weeks). Radiation leads to responses in about 80% of dogs, with almost 60% having complete remissions.
Carboplatin with piroxicam could be considered for patients with gross disease when more traditional therapies, such as surgery or radiation therapy, are declined or are not available. But according to Dr. Garrett, the studies on carboplatin’s effect on melanoma are retrospective, and more research is needed.1
A melanoma vaccine is available for dogs with oral melanoma as adjunct therapy. When counseling owners about the melanoma vaccine, Dr. Garrett advises that it is indicated in dogs that have had surgical removal of the primary tumor. And while no randomized studies have been performed, the vaccine may provide some dogs longer survival times.2,3
1. Brockley LK, Cooper MA, Bennett PF. Malignant melanoma in 63 dogs (2001-2011): the effect of carboplatin on survival. N Z Vet J 2013;61:25-31.
2. Tremayne J. Researcher eyes vaccines to treat canine skin cancer. DVM Newsmagazine 2005;36:22.
3. Bergman PJ, Camps-Palau MA, McKnight JA, et al. Development of a xenogeneic DNA vaccine program for canine malignant melanoma at the Animal Medical Center. Vaccine 2006;24:4582-4585.