Why is an early diagnosis of oral tumours in dogs important?

Many of the oral tumours in dogs can be cured, if they are diagnosed early. Therefore, do not waste precious time and consult your veterinarian as soon as you notice any change in your dog’s mouth.

A few different classifications are used to describe oral tumours in dogs, but the most important is to define their biologic behaviour and extent as soon as possible. Many oral tumours in dogs are benign (not harmful), others are benign, but locally aggressive (they will not spread to distant organs, but can grow extensively locally) and some are malignant (growing locally and also spread to other organs). In dogs, most of the oral tumours have excellent or at least very good prognosis, if diagnosed early and treated aggressively.

Canine acanthomatous ameloblastoma is one of the most common benign, but locally aggressive oral tumours in dogs. This tumour can grow extensively locally, but no distant spread (no metastatic disease) has been reported. Locally, it usually appears as a proliferative growth on the gingiva in the front (rostral) lower jaw, but it may appear anywhere on the parts of the jaws bearing teeth. Prognosis for the animal is excellent; if the tumour is small, surgical removal with 0.5 – 1 centimeter safety margin will result in cure and usually perfect functional and cosmetic outcome. Margins for the excision, however, should be planned based on advanced imaging (such as computed tomography, CT), as for all tumours!

Canine acanthomatous ameloblastoma is also very radiosensitive and can therefore be cured by radiotherapy as well. However, surgical removal is, if possible, preferable, especially in young animals, as long-term side effects of irradiation can occur.

The other very common benign oral tumour in dogs is peripheral odontogenic fibroma. This is usually a slow-growing lesion, that can invade the underlying bone, but is considered a reactive lesion by some professionals. It more commonly appears on the front part of the upper jaw, but any part of the dentate jaws can be affected. Prognosis for the animal is excellent, as surgical removal of this tumour results in cure, sometimes even with the lesion being only marginally excised.

However, even when a dog is diagnosed with a malignant oral tumour, several treatment options are available nowadays, that may result in cure of the animal or at least in prolongation of a good quality life. Treatment methods can be combined (multimodal treatment approach) to achieve the best possible outcome. Therefore, do not delay any diagnostic procedures and start with the treatment as soon as possible, as this gives the animal the best chances for a good outcome.

The most common oral malignant tumour is squamous cell carcinoma, which most commonly occurs on the jaws, but oral mucosa and tongue can also be affected. This tumour is invasive and will affect surrounding tissues, including bone. Metastases (spread of the tumour cells to other organs) occurs relatively rarely (about one third of the cases) and late in the disease. Therefore, oral squamous cell carcinoma in dogs is considered curable, if detected and aggressively treated early in the course of the disease. Surgical removal with at least 1 centimeter safety margin based on advanced imaging is the golden standard of treatment.

However, if the tumour is deemed inoperable or surgery results in unclean resection margins, radiotherapy is the treatment of choice. Survival in this case depends on tumour location and age of the animal, with younger animals having better prognosis. When tongue or tonsils are involved, the prognosis is poorer, as squamous cell carcinoma in this location behaves more aggressively.

Malignant melanoma is the other very common tumour of the oral cavity in dogs. Its’ appearance may vary greatly and pathohistology may be challenging as well. Prognosis for this tumour is, unfortunately, poorer compared to other tumours of the oral cavity in dogs. Even with a good local control of the disease, the tumour spreads early and commonly to other organs, especially regional lymph nodes and lungs. Early diagnosis is very important, as dogs with small tumours (smaller than 2 centimeters in diameter) and no metastatic disease have much better prognosis, especially with radical treatment. Surgical removal is the golden standard to control local disease, but to achieve better local and systemic control of the disease, other treatments are commonly included – most commonly radiotherapy, melanoma vaccine, electrochemotherapy and gene electrotransfer.

Fibrosarcoma and osteosarcoma can also affect oral cavity of dogs; achieving local control of the disease is challenging for both, hence early diagnosis is, again, extremely important. Plasmacytoma can be well controlled locally, unless it is a part of systemic disease. Lymphoma and mast cell tumour are both considered a part of systemic disease and are treated accordingly.

Several other lesions can affect oral cavity of dogs, either neoplastic (cancerous lesions) or not. To the naked eye, all lesions can look similar, therefore it is of an utmost importance to obtain a biopsy of any oral lesion to determine its’ nature.

If you have noted any problems with your animal, please consult your veterinarian.

Selected references
1. Celeste R, Bonello D, Verstraete FJM (2020). Nonneoplastic proliferative oral lesions. In: Verstraete FJM, Lommer JM, Arzi B eds. Oral and maxillofacial surgery in dogs and cats. 2nd ed. Elsevier, St. Louis, MO, pp. 452-462.
2. Gieger T, McEntee MC (2020). Clinical behavior of nonodontogenic tumors. In: Verstraete FJM, Lommer JM, Arzi B eds. Oral and maxillofacial surgery in dogs and cats. 2nd ed. Elsevier, St. Louis, MO, pp. 428-442.
3. Fiani N, LOmmer MJ, Chamberlain TP (2020). Clinical behavior of odontogenic tumors. In: Verstraete FJM, Lommer JM, Arzi B eds. Oral and maxillofacial surgery in dogs and cats. 2nd ed. Elsevier, St. Louis, MO, pp. 443-451.
4. Murphy BG, Bell CM, Soukup JW. Veterinary oral and maxillofacial pathology.John Wiley & Sons, Inc., Hoboken, NJ, 2020.