December 15, 2017

AVMA 2017: Managing Oral Tumors in Dogs

Early recognition and diagnosis, appropriate staging, and timely treatment elicit the best prognosis for these patients.
By Nicola M. Parry, BVSc, MRCVS, MSc, DACVP, ELS
Early detection and prompt treatment can lead to good outcomes for dogs with oral tumors, but veterinarians need to know how to spot these lesions, according to Erin D. Vicari, VMD, DAVDC, of the Animal Emergency and Referral Center of Minnesota in Oakdale. In a lecture at the 2017 American Veterinary Medical Association Convention in Indianapolis, Indiana,

Dr. Vicari said that oraltumors make up 6% of all tumors in dogs and discussed the need for clinicians to recognize and treat these tumors promptly. “Early detection of oral tumors directly correlates with clinical prognosis for many tumor types,” she said, noting that many good treatment options are available to help clinicians manage these tumors.

Clinical Signs
To facilitate prompt diagnosis, Dr. Vicari advised clinicians to be aware of how the lesions may present. Oral tumors may be associated with many or no clinical signs, which—when they occur—may include a visible mass, swelling, facial deformity, bleeding, chewing difficulty, reduced appetite, or weight loss.

Dr. Vicari advised clinicians always to perform a thorough oral examination, as well as an extraoral one, during routine annual examinations or dental cleanings, even in the absence of a clinical problem in a dog’s oral cavity.

Tumor Classification
Oral tumors are typically classified into 3 categories, Dr. Vicari said: odontogenic tumors and cysts, nonodontogenic tumors, and inflammatory or reactive lesions. She discussed common types from each category, urging clinicians to be aware of changes in the nomenclature of oral tumors.

Odontogenic Tumors and Cysts
These arise from embryologic structures associated with tooth development, Dr. Vicari said. The most common odontogenic tumor is canine acanthomatous ameloblastoma (formerly known as acanthomatous epulis). Although benign, it is locally aggressive and can invade bone. However, wide surgical excision of the tumor (with 1- to 2-cm margins where possible) is considered curative. Surgical resection is also preferred over radiation therapy, she added, because up to 20% of irradiated canine acanthomatous ameloblastomas undergo malignant transformation.

Odontoma is another benign odontogenic tumor. It has mixed mesenchymal and epithelial origins and predominantly arises in young dogs. This tumor typically is encapsulated, presents along the dental arch, and has characteristic radiographic features. According to Dr. Vicari, a compound odontoma has evidence of identifiable tooth components known as denticles throughout the mass, whereas a complex odontoma appears as an irregular mass of calcified material. Although odontomas also are locally aggressive, their early diagnosis allows for marginal surgical excision, which is considered curative.

Amyloid-producing odontogenic tumors (formerly known as calcifying epithelial odontogenic tumors) are uncommon, benign, expansive tumors that appear as gingival enlargements, Dr. Vicari said. Again, wide surgical excision is considered curative.

Peripheral odontogenic fibroma (formerly known as fibromatous and ossifying epulis) is a benign, often slow-growing tumor that arises from periodontal structures. Although surgical excision is curative, Dr. Vicari noted that extracting the involved teeth with complete excision of the associated bone and periodontal ligament tissues may also be required.

Dentigerous cysts arise from embryologic structures associated with unerupted teeth. Although benign, these lesions can expand and destroy surrounding bone and teeth. Surgical excision must include debridement and complete removal of the unerupted tooth and associated cyst lining, Dr. Vicari said. However, she emphasized that pre-vention is the best approach and recommended that clinicians extract any unerupted teeth.

Nonodontogenic Tumors
In dogs, most nonodontogenic tumors are malignant, Dr. Vicari said, and commonly include melanoma, squamous cell carcinoma, fibrosarcoma, and osteosarcoma.

Malignant melanoma is the most commonly reported oral tumor in dogs, predominantly arising in older patients. Melanoma is highly metastatic, Dr. Vicari said, so clinicians should presume that metastasis has occurred until proven otherwise. She noted that tumors smaller than 2 cm in diameter are more likely to have a better prognosis. Similarly, tumors with a low mitotic index may not have metastasized at the time of diagnosis, thus improving clinicians’ chances of gaining local control. Treatment requires wide surgical excision of the tumor, she said, and recommended referral to an oncologist for adjunctive treatment (radiation therapy, immunotherapy, vaccine, or chemotherapy).

Squamous cell carcinoma is the sec-ond most common oral tumor in dogs, Dr. Vicari said. It typically presents as an erythematous and ulcerated lesion, may arise anywhere in the oral cavity, and is locally aggressive and osteolytic.

Squamous cell carcinoma can metastasize but tends to do so later in the disease, she said, so wide surgical excision can be curative. She advised clinicians to take a biopsy sample from any unusual or unexpected lesion in the oral cavity, including from nonhealing extraction sites or regions where teeth may have fallen out unexpectedly. Treatment options include wide surgical excision with adjunctive radiation therapy.

Fibrosarcoma is the third most common tumor in dogs and occurs more frequently in older, large-breed dogs, Dr. Vicari said. Fibrosarcomas in the oral cavity typically are histologically low grade but biologically high grade, with metastasis occurring in about 20% of cases. Because of the tumors’ aggressive biological behavior, Dr. Vicari advised clinicians that wide surgical excision is needed.

When osteosarcoma occurs orally in dogs, it arises more frequently in the mandible than in the maxilla, Dr. Vicari said. However, in general, compared with osteosarcoma in the appendicular skeleton, osteosarcoma in the oral cavity is less common, has a lower metastatic potential, and thus carries a better prognosis with wide surgical excision.

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