3 key questions in prognosis and treatment of animals with oral tumors

Oral tumors represent 5.4% of all tumors in dogs and 7.4% of all tumors in cats and they can be benign, benign but locally aggressive, or malignant. Therefore, before any treatment is attempted, a patient with an oral tumor needs to be properly staged – we need to know, what the tumor is, how extensive it is and if malignant, if there is any metastatic disease.

What the tumor is?

To determine the nature of the tumor biopsy should be performed as soon as possible. Biopsy (tissue sampling for further diagnostic tests) is ideally taken following computed tomography (CT) to best plan the biopsy area, avoid superficial inflammation and any areas of necrosis. The biopsy is ideally undertaken by the surgeon who plans to carry out the definitive treatment, otherwise the biopsy site/track must be well documented in order to be later included in the surgical or irradiation field.

How big is the tumor?

To further evaluate local disease, tumor location is noted (photographed) and the lesion measured. What we see usually underestimates the extent of the lesion. Diagnostic imaging of the local lesion should include pre- and post-contrast CT of the head, especially for bigger tumors, tumors located caudally and/or maxillary tumors. Skull radiographs and/or intraoral dental radiographs will greatly underestimate the extent of the lesion and especially invasion of maxillary tumors into adjacent structures. Magnetic resonance imaging (MRI) can also be considered, especially for oral tumors located in the caudal oral cavity and/or oropharynx, and PET/CT is becoming available in veterinary medicine as well.

Where has the tumor spread?

If the tumor is malignant in its nature, evaluation of the regional lymph nodes and distant organs is needed to complete the staging.

Evaluation of regional lymph nodes may be challenging and the veterinarian should consider advantages and disadvantages of each procedure, also in view of the biologic behaviour of the local tumor. Palpation of the mandibular lymph nodes alone is very unreliable as palpably normal lymph nodes can contain metastases. Fine needle aspiration (FNA) of the regional lymph nodes may be helpful, but reaching the main draining center of the head – retropharyngeal lymph nodes – requires ultrasound-guided approach. Also, negative FNA result does not rule out metastases. Evaluation of size and contrast-enhancement pattern on post-contrast CT images may be helpful in evaluating regional lymph nodes for metastases, and PET/CT is also very promising, but not yet widely available. Excisional biopsy of the lymph nodes is debatable, as complete staging requires removal of all lymph nodes of the head and neck as the pathways of lymphatic drainage may be unpredictable. Nowadays, techniques to determine the sentinel lymph node are being developed to enable targeted excisional biopsy of the lymph node(s) most likely first affected by metastases.

Staging is completed with evaluation of distant organs for possible metastatic disease, where chest CT is much more sensitive to diagnose pulmonary metastasis compared to thoracic radiographs. Abdominal ultrasound or full-body CT may be recommended to fully evaluate the patient’s health status.

Only once the patient is fully staged and the disease properly classified using the TNM classification, the prognosis and treatment plan can be discussed with the client.

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

Selected references
1. Arzi B, Verstraete FJM (2012). Clinical staging and biopsy of maxillofacial tumors. In: Verstraete FJM, Lommer JM, eds. Oral and maxillofacial surgery in dogs and cats. Edinburgh, Saunders Elsevier, pp. 373-380.
2. Ghirelli CO, Villamizar LA, Pinto AC (2013). Comparison of standard radiography and computed tomography in 21 dogs with maxillary masses. J Vet Dent 30(2):72-76.
3. Green K, Boston SE (2017). Bilateral removal of the mandibular and medial retropharyngeal lymph nodes through a single ventral midline incision for staging of head and neck cancers in dogs: a description of surgical technique. Vet Comp Oncol 15(1):208-214.
4. Grimes JA, Matz BM, Christopherson PW, Koehler JW, Cappelle KK, Hlusko KC, Smith A (2017). Agreement between cytology and histopathology for regional lymph node metastasis in dogs with melanocytic neoplasms. Vet Pathol 54(4):579-587.
5. Grimes JA, Secrest SA, Northrup NC, Saba CF, Schmiedt CW (2017). Indirect computed tomography lymphangiography with aqueous contrast for evaluation of sentinel lymph nodes in dogs with tumors of the head. Vet Radiol Ultrasound 58(5):559-564.
6. Herring ES, Smith MM, Robertson JL (2002). Lymph node staging of oral and maxillofacial neoplasms in 31 dogs and cats. J Vet Dent 19(3):122-126.
7. Nemanic S, London CA, Wisner ER (2006). Comparison of thoracic radiographs and single breath-hold helical CT for detection of pulmonary nodules in dogs with metastatic neoplasia. J Vet Intern Med 20(3):508-515.
8. Randall EK, Kraft SL, Yoshikawa H, LaRue SM (2016). Evaluation of 18F-FDG PET/CT as a diagnostic imaging and staging tool for feline oral squamous cell carcinoma. Vet Comp Oncol 14(1):28-38.
9. Skinner OT, Boston SE, Souza CHM (2017). Patterns of lymph node metastasis identified following bilateral mandibular and medial retropharyngeal lymphadenectomy in 31 dogs with malignancies of the head. Vet Comp Oncol 15(3):881-889.
10. Skinner OT, Boston SE, Giglio RF, Whitley EM, Colee JC, Porter EG (2018). Diagnostic accuracy of contrast-enhanced computed tomography for assessment of mandibular and medial retropharyngeal lymph node metastasis in dogs with oral and nasal cancer. Vet Comp Oncol 16(4):562-570.
11. Smith MM (2002). Surgical approach for lymph node staging of oral and maxillofacial neoplasms in dogs. J Vet Dent 19(3):170-174.