The diagnostic approach to oral masses

Photo: Petra Richli/Adobe Stock

A boxer with gingival hyperplasia.

“Good oral exams can save lives,” said Naomi Hoyer, DVM, DAVDC, assistant professor of dentistry and oral surgery at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences in Fort Collins. Lifting the lip during every physical examination can help veterinarians to identify oral masses when they are small.¹

“We can fix oral cancer a lot of the time when it’s found early,” Hoyer stated during a session at the 2024 Veterinary Meeting & Expo in Orlando, Florida.¹ “A lot of the early work up of oral neoplasia is doable in [general] practice,” she continued, providing general practitioners a road map for approaching oral masses in dogs and cats.

Identifying oral masses

Once an oral mass is identified, Hoyer encourages veterinarians to make an educated guess as to whether it is benign or malignant based on the characteristics of the mass. Important considerations are as follows¹:

• Tissue of origin: Benign masses most commonly arise from gingival tissue while malignancies can arise anywhere in the mouth.
• Pigmentation: Benign masses typically match the pigment of the surrounding tissue while malignancies are more likely to differ in color.
• Shape: Benign masses tend to be rounded while malignancies are more likely to be irregular.
• Bony destruction: Benign masses are less likely to destroy bone while malignancies can cause dramatic loss of bone.

The size of masses can vary greatly, regardless of whether they are benign or malignant. Size depends on how long the mass has been present and the type of mass. Additionally, surface ulceration can be present in both benign and malignant masses. With benign masses, ulceration may occur on masses that are in a location allowing for tissue trauma when the pet chews.

Malignancies are more likely to become ulcerated as they grow. Developing a differential diagnosis list for the mass allows veterinarians to plan how to obtain a definitive diagnosis and prepare the client for what comes next.

Biopsy tips and tricks

“Oral tumors do not exfoliate well,” said Hoyer. She recommended veterinarians skip aspiration and move right to a biopsy. However, she implored veterinarians to “please take pictures before you biopsy.” Photos can help the pathologist as well as provide essential information to the specialist who may perform follow-up treatment.

Incisional biopsies are preferred when malignancy is suspected. The tissue sample should be taken from the center of the lesion to avoid making a definitive surgery larger. Excisional biopsies are reasonable when benign lesions are suspected. Hoyer said that she tells her clients, “If I guess wrong and this is a malignant tumor, then we need more [treatment]. If I guess right, then we are done.”

When obtaining biopsies, it is important to avoid compromising adjacent teeth while collecting a large sample or multiple samples to maximize the ability to get a definitive diagnosis. Avoid the use of laser and cautery in the mouth.

Clients should be prepared for possible outcomes, including the need for referral for more definitive surgery pending biopsy results. For clients that are not interested in referral, having a definitive diagnosis can help to give a prognosis and set expectations for what the pet may experience.

Common oral masses in dogs

In dogs, a majority of oral masses—53.6%² to approximately 60%¹—are benign. Common benign lesions include gingival hyperplasia, peripheral odontogenic fibroma (POF), which was previously referred to as an epulis, and canine acanthomatous ameloblastoma (CAA). Common malignant lesions include oral melanoma, squamous cell carcinoma, and fibrosarcoma.

POFs are typically slow growing but can vary in appearance. They often arise in the gingiva overlying teeth, which makes them impossible to close. Owners should be advised that some postoperative bleeding is normal in these cases, but the tissue will heal quickly. Most of these growths are resolved by a conservative excisional biopsy. If they regrow, the adjacent tooth will need to be removed, as these can arise from the periodontal ligament.

CAAs are benign, locally aggressive tumors that occur most commonly in the rostral oral cavity. They can cause some bony destruction, which may lead to a suspicion of malignancy prior to biopsy. Hoyer cautioned that these nodules may grow more rapidly after biopsy is collected. A larger surgical excision is needed to remove these growths, but they rarely metastasize and have a good prognosis following definitive surgery.

Melanomas are the most common oral tumor in dogs. Although many are pigmented, an amelanotic variety exists. Owners should be prepared that these tumors grow quickly and often metastasize. Treatment involves large surgery and ancillary treatments such as immunotherapy or radiation with or without chemotherapy.

Squamous cell carcinomas are red, raised, ulcerated growths that typically cause extensive bony destruction and are likely to metastasize. Treatment includes wide surgical excision and radiation therapy. Prognosis is improved for masses present in the rostral oral cavity as definitive surgery is more feasible.

Fibrosarcomas are more common in large breed dogs. They can be cured by wide surgical resection as they are slow to metastasize. Hoyer cautions veterinarians to be aware of one variety of fibrosarcoma that is histologically low grade but biologically high grade. This variant may sometimes be called a POF on initial biopsy but may quickly regrow and cause bony destruction, which are behaviors that are atypical of a POF.

The most common oral mass of cats

When it comes to cats, “with very few exceptions, it is going to be squamous cell carcinoma,” said Hoyer. The majority of oral masses—approximately 58%² to more than 70%¹—of oral masses in cats are malignant. There are limited treatment options for these masses and the prognosis is poor, she noted.

Hoyer advised veterinarians to be vigilant in cat mouths as these tumors can have variable appearance. Whenever there are easy to extract teeth, she recommends collecting a bone biopsy from the surrounding bone. If the owner does not want to submit the sample right away, it can be kept and submitted if complications arise from the extraction site to evaluate for the presence of neoplasia.

Take home points

General practitioners should feel confident in their ability to begin a workup for oral masses in many patients. After careful evaluation of the appearance of the mass, a suspicion of whether the mass is benign or malignant can be developed. This suspicion will guide the approach to biopsy and client communication. Definitive surgery and ancillary treatment will often require referral to a specialist, but when caught early, many oral tumors in dogs can have good long-term prognoses. Unfortunately, oral masses in cats are more likely to be malignant and carry a much poorer prognosis.¹

References

1. Hoyer N. Oral neoplasia: I can help you work it up. Presented at VMX 2024: Orlando, FL. January 13, 2023.
2. Cray M, Selmic LE, Ruple A. Demographics of dogs and cats with oral tumors presenting to teaching hospitals: 1996-2017. J Vet Sci. 2020;21(5):e70. doi:10.4142/jvs.2020.21.e70