A sedated oral exam is an important step in the patient’s evaluation, allowing for a better gross evaluation of the extent of the tumor. An awake oral exam may be challenging, as an animal may not allow the clinician to open the mouth due to discomfort related to the presence of an oral mass. During the sedated oral exam, a biopsy of the mass should be obtained. Even if a good correlation exists between cytology and histology for oral tumors in dogs,⁴ the author prefers to obtain a deep, large biopsy to maximize the chance of having a definitive diagnosis. Electrosurgery can be used to collect a sample from the mass, but this may create artifacts that alter the sample’s quality. Multiple good quality, deep biopsies should be obtained to maximize the chance of obtaining a correct final diagnosis. A core punch or a wedge biopsy are considered appropriate techniques. The bleeding resulting from obtaining the biopsy can usually be stopped by compressing the area with a gauze, using electrosurgery, silver nitrate sticks, or suturing the edges of the biopsy site. It is not uncommon that the sutures placed to close the biopsy tract could cut through the friable neoplastic tissue, and for this reason, the author does not routinely use this technique. Biopsies must be obtained from an intraoral approach and from a location that will be resected with the mass at the time of surgery. If the size of the mass is small (<1 cm), an excisional biopsy can be considered. In this case, it is imperative to obtain pictures before removing the mass. This is because the oral mucosa heals quickly, and, in case of a diagnosis of a malignant tumor and the subsequent need for revision surgery, identifying the area where the mass was located could be extremely challenging. Documentation, especially in recording the teeth closest to the mass’s location prior to resection, is also pertinent for the medical record and for future intervention.

Obtaining a preoperative diagnosis is fundamental before considering surgical removal of a large oral mass. This information will help the clinician choose the appropriate surgical dose, suggest alternative treatment options (e.g., radiation therapy, chemotherapy, etc.), and give the owner information about the prognosis. Common malignant oral tumors in dogs are melanoma, squamous cell carcinoma (SCC), osteosarcoma, and fibrosarcoma.⁵ Benign tumors, like acanthomatous ameloblastoma and peripheral odontogenic fibroma, are not infrequent. Even if benign, canine acanthomatous ameloblastoma can invade the bone, and a mandibulectomy should be performed to decrease the chance of local recurrence. In cats, the most common tumor type is SCC, accounting for 70% of all oral tumors,⁵ but other tumors like osteomas, osteosarcoma, and odontogenic tumors can be encountered.

Skull CT scan, including the cervical region to assess lymph nodes, is the preferred method to assess the extent of oral neoplasia,⁶ as bony changes can be seen on radiographs only if 40% of the cortical bone is lost.⁷ For small rostral lesions, the use of intraoral radiographs may be adequate. Margins for both benign and malignant tumors should always be measured based on advanced imaging findings and not gross extension of the tumor. Different types of margins have been suggested for benign and malignant tumors. Some authors have suggested obtaining margins of 2–3 cm for malignant tumors affecting the mandible,⁷ while others suggested smaller margins (1–2 cm).³ The author tends to obtain margins of 1–2 cm for most malignant tumors, especially in small dogs and cats where the 2–3 cm margins would not be possible to achieve, and margins of 1 cm or less for benign tumors. Margins of 2–3 cm are usually attempted in dogs affected by oral fibrosarcoma, due to the high chance of local recurrence.⁸

It is important to remember that oral fibrosarcoma can appear as a benign lesion on histology even if it biologically behaves as an aggressive tumor (so‐called histological low grade‐biological high grade or “high‐low” tumors). The histologic diagnosis should always be correlated to the clinical behavior of the mass. Signalment is another important factor to consider, as retrievers seem to be more frequently affected by this type of tumor compared to other breeds. Signalment and biological behavior should always be relayed to the pathologist at the time of the submission of the biopsy sample to help in formulating a correct diagnosis.

Metastasis to locoregional lymph nodes is not uncommon in dogs with malignant oral tumors and is a negative prognostic factor.⁹ In dogs with oral melanoma, metastatic lymph nodes can be of normal size in 40% of the cases.¹⁰ Unfortunately, CT appearance of neck lymph nodes in dogs affected by oral and nasal tumors is not predictive of the presence of metastatic disease.¹¹ Some surgeons routinely perform full neck lymph node dissection for better staging of malignant oral tumors, but the clinical benefit is unknown. A possible alternative to this method is the sentinel lymph node mapping technique. With this technique, it is possible to identify the first lymph node within a lymphocentrum that drains lymph from a tumor. Once identified, a selective lymphadenectomy is performed. Different techniques for preoperative or intraoperative sentinel lymph node mapping have been described.^12–15 A thorough discussion of these techniques is outside the purpose of this chapter.

All malignant oral tumors can metastasize to the lung. Thoracic radiographs or thoracic CT scans should be performed before surgery. The author prefers to obtain a thoracic CT scan at the time of the head and neck CT performed for surgical planning, as this imaging technique has a higher accuracy for detecting pulmonary nodules compared to thoracic radiographs.¹⁶