Oral cavity neoplasia is common in dogs and cats. As a small animal clinician, it is imperative that you become familiar with the appearance and behavior of the different tumors; develop a consistent, effective diagnostic and staging approach; and learn to assess which tumors are actually treatable.

The clinical signs associated with oral neoplasia include excessive salivation or blood-tinged saliva, halitosis, dysphagia, and local infection. As oral tumors are often quite advanced at the time of diagnosis, the surgeon must exercise good judgment when determining surgical candidates. If a tumor is discovered when it is small, curative surgery is possible, even with invasive malignancies. Because distant metastasis often occurs late in the course of the disease, palliative surgery including hemimandibulectomy or partial maxillectomy is an option to consider.

The most common oral tumors in dogs are:

 Malignant:

 Malignant melanoma

 Squamous cell carcinoma

 Fibrosarcoma

 Osteosarcoma

 Benign:

 Epulides

The most common oral tumors in cats are:

 Squamous cell carcinoma

 Fibrosarcoma

Tumor Characteristics - Canine

1. Malignant Melanoma

 The most common oral malignancy in dogs. Poodles, Dachshunds, Scotties, and Goldens most commonly affected

 Characteristic pigmented, friable oral mass in an old dog

 Approximately 1/3 of tumors are amelanotic

 Aggressive local growth and regional and distant metastasis common. Although overall distant metastasis rate is high, it doesn't usually occur until late in the course of disease (6–12 months)

2. Squamous Cell Carcinoma

 Small-breed dogs are more commonly affected

 Very locally invasive

 Regional metastasis of gingival SCC uncommon (10% in one study). Regional metastasis at the time of diagnosis is more common with lingual SCC (43% in one study) and tonsillar SCC (85% in one study). Distant metastasis is uncommon with SCC.

**Tonsillar SCC in dogs is a very aggressive form of the disease. Marked swelling in the cervical area usually results from lymph node metastasis. Affected dogs may present with dysphagia, anorexia, and/or pain.

3. Fibrosarcoma

 Very locally invasive

 Large breeds more commonly affected and usually younger (at 7–8 years) than dogs with SCC or melanoma

 Tumors often advanced at the time of diagnosis

 More commonly affect the maxilla (72% in one report) than the mandible

 Metastatic potential is between that of malignant melanoma and SCC at 20%. Only 10% have pulmonary metastasis at the time of diagnosis.

**A subset of fibrosarcomas has been recognized in which the tumors appear histologically low-grade, yet behave high-grade.

4. Osteosarcoma

 Mandible and maxilla most common locations with osteosarcoma of the axial skeleton

 Maxilla:

 Locally invasive

 Metastasis detected at time of diagnosis uncommon (one report 0/11). Distant metastasis may be a late occurrence, with rates as high as 35–50% reported. Not clear whether this resulted from poor local control or undetectable pulmonary micrometastases at time of diagnoses.

 Mandibular:

 Locally invasive

 Mandibular osteosarcoma may not be as aggressive as OSA of the appendicular skeleton

 Metastasis uncommonly detected at time of diagnosis (5%). In one study, dogs with longer followup had incidence rate of 30%.

Epulides

There are three types of epulides: fibromatous, ossifying, and acanthomatous. All three tumor types arise from the periodontal ligament of the tooth.

 Fibromatous and ossifying epulides:

 Benign

 Rarely exceed 2 cm diameter

 Slow growing

 Acanthomatous epulis:

 Aggressive, invading into bone and surrounding tissue; however, do not metastasize

 Most commonly arise from the rostral mandible (incisors)

Tumor Characteristics - Feline

1. Squamous Cell Carcinoma

 Most common oral tumor in cats by far, accounting for 80%

 Very locally aggressive tumors

 Most occur at base of tongue and involve the frenulum

 Bone invasion common with gingival tumors

 Lymph node metastasis reported to be 15%

2. Fibrosarcoma

 Second most common oral tumor in cats

 Most commonly affects gingiva

 Locally invasive

 Low metastatic potential

Diagnosis

 Aspirate/cytology of 1° tumor usually not diagnostic (except for malignant melanoma).

 Incisional biopsy usually preferred over excisional (allows for planning based on tumor identity).

 Evaluation (aspirate or biopsy) of regional lymph nodes (esp. with tonsillar SCC) essential. One report found a higher sensitivity of regional metastasis detection when the mandibular, parotid and medial retropharyngeal lymph nodes were all surgically removed and examined.

 Thoracic radiography to evaluate for distant metastasis.

 Radiographs +/- CT scan to determine extent of bony invasion. The majority of the malignant tumors will have evidence of bony involvement at the time of diagnosis. Radiographic evidence of lysis does not occur until 50% of bone has become demineralized.

 Postoperative radiographs of the excised portion of the mandible or maxilla can help confirm that adequate margins were achieved.

 Abdominal ultrasound indicated with tonsillar SCC, as distant metastasis is more common to the liver and spleen than to the lungs.

Treatment

Melanoma

 Aggressive surgical excision including partial mandibulectomy/maxillectomy if necessary.

 Radiation may have a role for effectively treating the 1° tumor.

SCC

 Aggressive surgical excision including [sic] if necessary. With a lingual tumor location, dogs do surprisingly well with near total excision of the tongue.

 Radiation has been recommended following surgical excision to treat "dirty" margins in tumors too large to obtain adequate margins.

FSA

 Aggressive surgical excision to include part of mandible or maxilla if necessary.

 Radiation has been recommended to treat "dirty" margins in tumors too large to obtain adequate margins.

Osteosarcoma:

 Mandibular: Aggressive partial or hemimandibulectomy

 Maxillary: Aggressive partial maxillectomy

 Fibromatous and ossifying epulis:

 Partial mandibulectomy/maxillectomy including the affected tooth socket is curative

 Local excision rarely curative, but is an option for fibromatous and ossifying since they are so slow growing and noninvasive

Acanthomatous Epulis

 Partial mandibulectomy/maxillectomy must include the affected tooth socket and a margin (1–2 cm) of normal bone

 Radiation therapy very effective

Feline SCC

 Aggressive surgery for rostrally located tumors followed by radiation +/- chemotherapy

 Many of these tumors are advanced at the time of diagnosis and many, especially large tumors under the tongue, are inoperable or their removal would negatively impact the quality of life for the cat. Radiation therapy alone has not shown much promise (MST 170 days).

Feline FSA

 Aggressive surgery +/- radiation

 Vincristine caused complete regression of an oral FSA in one cat when treated for 30 weeks

**Cryosurgery can be useful for palliation of fairly small tumors in difficult-to-treat locations (such as caudally located SCCs), local recurrences, and in cases where owners are not interested in aggressive surgery.

Prognosis

Melanoma: Poor to Grave

 Tumor size is very important

 Stage I: <2 cm

 II: 2–4 cm

 III: >4 cm or bone invasion and positive lymph node

 IV: Any of above and distant metastasis present (us. lungs).

 One study showed median survival time (MST) of 511 days for stage I, and 164 days for stage II and III.

 Local recurrence rate is high (34/49 cases, 33 of which developed metastases), although one report achieved a recurrence rate of <15% with mandibulectomy. In three studies, dogs treated with aggressive surgery had survival times of 7–9 months.

SCC: Fair to Poor to Grave (Tonsillar)

 However, the prognosis is better than for melanoma and fibrosarcoma, especially if the tumors are rostral and small, as they are more amenable to aggressive surgery.

 Local recurrence is common in all forms of SCC.

 The relatively low rate of metastasis of gingival SCC makes it a good candidate for local therapy (i.e., surgery and radiation). With aggressive mandibulectomy and maxillectomy, the MST has been reported to range from 9 to 18 months.

 In one report of lingual SCC, 5 dogs treated with surgery alone had a median survival of time of 8 months. Three of these dogs had local recurrence.

 Survival times for tonsillar SCC are low. The most successful treatment reported is surgery, radiation, chemotherapy combined, achieving a MST of 240 days, although 4/6 of the dogs in this study developed local recurrence and metastatic disease.

FSA: Guarded to Poor

 Local recurrence is common even after aggressive surgery (37% in one study). This may be partly due to the fact that most are associated with the maxilla and are thus more difficult to completely excise.

 MST 12 months with aggressive surgery.

 Surgery combined with radiation therapy may be the best option.

Osteosarcoma: Fair to Poor

 Mandibular: Mandibulectomy (partial or hemi) alone may provide good control of this tumor. In one report, 73% of 23 dogs treated by mandibulectomy were still alive 1 year after surgery.

 Maxillary: Local recurrence is common. With aggressive surgery, recurrence rates as low as 25% with up to 45% of dogs alive after surgery have been reported.

 Chemotherapy and radiation, for either form, have not been associated with an increase in survival.

Fibromatous and Ossifying Epulis: Excellent

Acanthomatous Epulis: Good with Proper Treatment

Feline SCC: Guarded to Grave

 In one report of SCCs treated by mandibular resection alone, 4/5 cats had local recurrence within 5 to 12 months of surgery. These tumors were large and all invaded bone. In another study, in which mandibulectomy was followed by radiation, better results were achieved; however, 6/7 still had local recurrence with a median time of 12.5 months.

 Complete excision is possible with rostrally located small tumors, but these circumstances are rare.

Feline FSA: Guarded

 Few reports available

 Two cats treated with hemimandibulectomy or pre-maxillectomy were free of disease at 11.5 and 24 months. Another cat treated with surgery had local recurrence within 2 months.

Surgery

Prior to surgery, a thorough oral exam should be performed under general anesthesia. Along with radiographic or CT studies, a decision is made on how much tissue to excise. Wide surgical margins (2–3 cm) around the tumor should be obtained. For most tumors, this includes either partial mandibulectomy or partial maxillectomy. These procedures are discussed below.

Mandibulectomy

Mandibulectomy is a contaminated procedure. Therefore, intravenous antibiotics are usually given perioperatively. The types of mandibulectomy are described below:

Rostral Mandibulectomy

Tumors involving the incisors, lower canines or first two premolars on one side of the mandible are indications for unilateral rostral mandibulectomy. A bilateral rostral mandibulectomy is indicated for tumors that cross the midline rostral to the second premolar.

The lower lip is clipped to the angle of the jaw and prepared in routine fashion. With the animal in lateral recumbency, the buccal mucosa is incised 1 cm lateral to the visible limits of the disease. The lingual mucosa is then carefully dissected to avoid damage to the sublingual and mandibular salivary gland ducts which open just lateral to the frenulum of the tongue. If excision of this area is necessary, an attempt is made to ligate these ducts. For unilateral rostral mandibulectomy, the mandibular symphysis is split with an osteotome, gigli wire, or oscillating saw. Because the body of the mandible is brittle, a saw or gigli wire is used to make the caudal osteotomy. Use of an osteotome here may fracture the mandible. After making this caudal incision, the mandibular canal will be exposed and the mental artery and vein, and mandibular alveolar artery, vein and nerve will be visible. Hemorrhage from the mandibular canal and medullary cavity is often significant and must be controlled with cautery, ligation, or bone wax.

If bilateral rostral mandibulectomy is required, the mandibular symphysis is not split, but the mandible is osteotomized caudal to the tumor on that side. After removing the tumor from the adjacent soft tissue, both hemimandibles are freely movable. No attempt is made to connect the rami together.

Closure of the wound is one layer. The oral sublingual mucosa is apposed to the buccal mucosa using 3-0 or 4-0 interrupted sutures. If the pigmented portion of the lip is free of tumor, it is preserved to help act as an anti-drool mechanism. In some cases of aggressive rostral mandibulectomy (back to the 4th premolar), redundant skin must be excised. This is best done by making a V-shaped incision on the rostral extent of the skin with the apex located ventrally. This incision is closed in three layers, closing the subcutaneous layer first, mucosal layer (sublingual to buccal), and then skin.

Hemimandibulectomy

Total or partial hemimandibulectomy involves either the removal of the entire hemimandible including the temporomandibular joint (TMJ) or may involve the entire body of the hemimandible up to the angular process.

The animal is placed in lateral recumbency, and the entire side of the face is clipped and prepped to the level of the eye. A full-thickness incision through the commissure of the lip (commissurotomy) is made to the rostral edge of the vertical ramus. The incision is then continued through the skin, avoiding the masseter muscle to the level of the TMJ. Branches of the facial artery and vein are ligated or cauterized as needed. The parotid duct can usually be avoided, as it runs dorsal to this incision. The mandibular symphysis is split using an osteotome, and the labial and buccal mucosa are incised from the rostral mandible and extended caudally to the angle of the mandible. The genioglossus, geniohyoideus, and mylohyoideus muscles are cut where they attach on the medial surface of the mandible. With lateral retraction of the mandibular body, the pterygoid muscles are incised where they insert medially on the intracaudal surface of the mandible. The mandibular alveolar artery and vein can then be identified and double ligated prior to their entrance into the mandibular foramen.

If a partial hemimandibulectomy is performed, an oscillating saw is used to make a cut 1 cm caudal to the last molar tooth extending down through the angular process of the mandible. The digastricus muscle is then separated from the ventral surface of the remaining mandible bone, and the resection has been complete.

If a complete hemimandibulectomy is performed, the masseter muscle is sharply dissected off the ventral lateral surface of the mandible, and retracted dorsally, exposing the TMJ. The joint capsule is incised, and a periosteal elevator is used to remove the temporalis muscle as it inserts on the coronoid process of the mandible.

A three-layer closure is recommended. The deep layer consists of apposing the pterygoideus, masseter, and temporalis muscles. Subcutaneous closure, using 3-0 or 4-0 absorbable monofilament in a simple continuous pattern, then apposes the lingual and buccal mucosa. A simple interrupted pattern is then used (also absorbable monofilament) to suture the mucosa.

Removal of the entire hemimandible results in loss of lateral support, and the dog's tongue may hang out of the side of the mouth. To correct this problem, a cheiloplasty may be performed. The pigmented portion of the upper and lower lip are incised full thickness to the level of the upper canine tooth. A three-layer closure consisting of the mucosa, subcutaneous tissue, and skin is then performed. Since there will be excessive tension on the rostral extent of the suture line, a stent suture using buttons or rubber tubing is recommended.

**In general, cats do not tolerate hemimandibulectomy as well as dogs. Unlike dogs, some cats will refuse to eat due to the malocclusion that results from mandibular drift. For this reason, some surgeons recommend against this procedure in cats.

Maxillectomy

Partial maxillectomy is indicated for excision of malignant oral tumors and benign oral tumors that involve bone or periosteum.

Partial maxillectomies are described according to the areas excised (i.e., premaxilla, central, caudal, hemimaxilla). Excision is limited by the amount of normal labial or buccal mucosa and hard palate mucoperiosteum that is available for closure of the oronasal defect that results. As much as half the width of the hard palate may be resected.

The preparation for the procedure is similar to that of mandibulectomy. A mucosal incision surrounding the tumor, including wide margins (2–3 cm if possible) of normal tissue, is made through the labial, buccal, and gingival mucosa and the mucoperiosteum of the hard palate. Hemorrhage from the branches of the infraorbital artery and vein or major palatine artery is controlled with electrocautery or vessel ligation. A periosteal elevator is then used to expose the underlying bone. The bone is then cut along the same line as the mucosal incision with an oscillating saw or osteotome. This loosens the section of tissue containing the tumor, and allows the remaining attachments of nasal turbinates and nasal mucosa to be severed. The resulting oronasal defect is then repaired. To minimize tension on the closure, a mucosal-submucosal labial flap is created with Metzenbaum scissors, using sharp and blunt dissection, from the upper lip lateral to the defect. This flap is then sutured to the hard palate mucoperiosteum with two layers of simple interrupted sutures of a synthetic absorbable suture. The degree of facial deformity following partial maxillectomy depends on the extent of excision and the surgeon's ability to minimize tension on the incision by creating a labial flap. Cosmetic defects are minimal if the ipsilateral canine tooth is left intact, with the most marked cosmetic deformity occurring following a bilateral rostral maxillectomy which includes excision of both upper canine teeth.

Postoperative Care and Complications

Analgesics are continued for at least 24 hours, postoperatively. Intravenous antibiotics are usually not given for more than 24 hours. An Elizabethan collar is placed to prevent scratching and mutilation of the wound. Ice cubes may be given to reduce oral swelling the evening of surgery. The following day, free-choice water and a liquefied gruel diet or canned food "meatballs" are offered. The surgical site is kept clean of debris by flushing the mouth with water daily. Dehiscence of part of the closure is not uncommon but can be kept to a minimum if electrocautery is not overused during the surgery. Small areas of dehiscence will granulate and epithelialize without any further surgery. A ranula (accumulation of saliva from damaged salivary tissue) may develop under the tongue if the sublingual and/or mandibular salivary ducts have been transected and not ligated. A major long-term complication is a phenomenon called "mandibular drift." Because of the lack of support, the contralateral mandible will move toward the midline, and there is potential for the lower canine tooth to "strike" the roof of the mouth. If this problem becomes severe, tooth extraction of the involved canine usually alleviates the problem. Another complication is refusal to prehend food after the surgery. When performing oral cavity surgery, the surgeon should always consider the postoperative use of feeding tubes, especially in cats.

Oronasal fistula formation is a potential complication following partial maxillectomy. Factors that seem to predispose wound dehiscence and oronasal fistula formation are tension on the oral suture line, and inadequate suture placement. Ulceration may occur on the mucosa of the labial flap or the skin of the lateral surface of the lip. This is usually a temporary problem that resolves as swelling of the upper lip subsides. Another potential complication is damage to adjacent teeth. If the tooth root is damaged, the tooth may die and later require extraction.

Local tumor recurrence occurs in approximately 1/3 of the tumors regardless of histologic type. Caudal maxilla tumor location, the absence of tumor-free surgical margins and histologic evidence of malignancy all worsen the prognosis.