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Oral Dog Tumors: How to Tell If They're Benign or Malignant

Updated: Aug 11, 2023

As we all know, dogs are quite prone to cancers, and those cancers can manifest in a lot of different ways. Sometimes, they're obvious lumps or bald patches that are noticed and diagnosed quickly, but other times, they slip by in hidden places until they grow too big to ignore. Unfortunately, all too often, by the time they're noticed, they're past the point of easy treatment.

Oral tumors are one of the trickier cases in dog cancer treatment because the inside of the mouth is hidden enough that many pet owners don't check or inspect the area as frequently as they should. While it's part of a vet's comprehensive checkup, annual inspections can miss things.

What Are the Risk Factors for Oral Tumors in Dogs?

Unfortunately, cancer isn't a single illness, so it's difficult to pin down any specific cause or risk factor.

It's always a combination of genetics, environmental factors, exposure to viruses and other diseases, and much more.

"Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Male dogs appear to be twice as likely to develop oral cancer than female dogs. Several breeds seem to be more predisposed to oral cancers including Akita, Cocker spaniel, Collie, Boxer, Dachshund, Doberman pinscher, Golden Retrievers, Poodle, Scottish terrier, and Shetland sheepdog." – VCA Animal Hospitals.

Often, oral tumors go unnoticed for an extended period before they reach a size where they cause pain, obstruct eating or breathing, ulcerate and bleed, displace teeth, or cause other problems. At this point, swift diagnosis is critical to develop an appropriate treatment plan.

What Are the Symptoms of Oral Tumors in Dogs?

Oral tumors can range anywhere from so minor that they're barely noticeable all the way to painful and disfiguring growths. Often, however, there are a set of symptoms that a dog might display that indicates something wrong with their mouth, at which point a pet owner can look for a tumor or other problem, and a vet can take up that inspection and escalate to a full diagnosis.

"Pets with oral tumors will often have a history of pain while trying to chew or swallow food, food dropping out of the mouth while eating, drooling, or not willing to eat at all. Periodontal disease, bad breath, and tooth loss may also be noted. If lesions are ulcerated, there may be blood-tinged saliva. By the time any abnormality is noticed, the mass is likely to be large enough to be visualized in the oral cavity." –

If a dog is displaying symptoms such as difficulty eating or aversion to food, excess drooling, and bloody saliva, a swift inspection is required to identify if there are wounds, lumps, tumors, or other issues causing it.

These symptoms are generally the same set of behaviors for all kinds of oral issues, so they don't necessarily indicate a tumor; they can also be indicative of a mouth injury like a laceration caused by a stick or bone, a broken tooth, or even gum disease.

What Are the Most Common Oral Tumors in Dogs?

Oral tumors can be both benign and malignant, though even benign tumors can cause enough of a problem that they need to be addressed.

The most common benign tumors are peripheral odontogenic fibromas, which are firm masses involving the tissue of the gums around a tooth and the periodontal ligament of the affected tooth. Focal fibrous gingival hyperplasia is also a very common oral lesion resulting in overgrown gums.

Another common benign tumor is the canine acanthomatous ameloblastoma, a locally aggressive tumor that invades many nearby tissues, including bone, and requires aggressive surgery to remove. It doesn't metastasize like a cancer could, but it grows rapidly and affects everything in the area, making it especially important to get all of it when removing it.

As for malignant tumors, there are three specific cancers that occur most frequently in dog mouths.

"In dogs, the three most common malignant oral tumors are malignant melanoma, squamous cell carcinoma, and fibrosarcoma." – Merck Manual.

Identifying the nature of an oral tumor is necessary for creating a treatment plan for a given patient. There are no standard, one-size-fits-all treatment options.

What's the difference between benign and malignant tumors?

Though vets generally know this already, it can be worthwhile to review the differences in simple terms to make it easier to explain to a pet owner.

Often, there's a misconception that benign tumors are not dangerous and don't need attention. The word "benign" itself means gentle, harmless, or otherwise not dangerous. Unfortunately, that's not true.

The biggest difference between benign tumors and cancerous/malignant tumors is that they don't spread. They grow, and they can invade surrounding tissues, but they typically don’t metastasize to other locations in the body.

Benign tumors can still grow to the point where they cause damage, loss of function, and worse. However, they can usually be removed with surgical resection and generally don't require systemic treatments like chemotherapy.

Conversely, malignant tumors, or cancers, can spread. Stray cells can migrate throughout the body via the lymphatic or vascular systems, and those stray cells can take root and grow as secondary tumors. Cancers, then, require systemic treatment to handle.

Another common misconception is speed. Often, pet owners will have an assumption that benign tumors are slow or do not grow, while malignant tumors grow quickly. While this is generally true, in broad strokes, it's not universally true. Some benign tumors grow quite quickly, which is another way in which it can be difficult to distinguish tumors by inspection.

Can Oral Tumors be Identified Through Visual Inspection?

A common question vets are asked by concerned pet owners is, "Well, what does it look like?"

Unfortunately, there's no real way to determine with certainty what a tumor is on visual inspection. While some look distinct, there are enough different kinds of general swelling and masses that a visual inspection alone is not adequate.

For example, here's VCA on melanomas:

"Melanomas appear pigmented or non-pigmented and may be nodular or cauliflower-like in appearance. These tumors may appear as swellings on the gums around the teeth or on the hard or soft palates. They frequently ulcerate (break open) and bleed. They may also become infected. These tumors may look small but may extend deeper into the tissues than expected, invading the underlying bone."

There's enough variation that it's impossible to say with certainty what's going on. That said, different tumors often have a certain range of appearances, and you can get a broad, general idea of what you might be looking at. For example, from Veterinary Cancers:

"Malignant melanomas of the oral cavity originate from the mucosa or gingiva. They often have brown or black pigmentation but can also be non-pigmented. Male dogs with heavily pigmented mucosa, such as German Shepherds and Cocker Spaniels, may be more predisposed. Malignant melanomas are characterized by rapid growth, local invasiveness, and early metastasis to regional lymph nodes and lungs."

"Fibrosarcomas arise from the gingiva or connective tissue of the hard palate. They often appear firm and smooth with nodules that may become ulcerated and can be seen on the upper jaw between the canine and molar teeth."

"These masses [tonsillar squamous cell carcinomas] appear as plaque or cauliflower-like lesions often affecting only one tonsil."

As you can see, there's a lot to consider, even with just a relatively small subset of potential tumors.

How is an Oral Tumor Diagnosed?

The process of diagnosing a tumor involves several steps.

The first step is generally a fine needle aspiration. This aspiration uses a very thin needle to draw out the liquid or cells from within the lump, which is then sent off for an examination and testing to determine what the tumor is likely to be. An aspiration alone won't generally give the specific information necessary to deliver a treatment plan, but it can identify the class of tumor in broad strokes.

At this point, additional tests can be performed. These include bloodwork, which can identify if any metrics are out of line with the normal baseline for the age, breed, and other medical conditions the dog may have. Bloodwork can help indicate systemic issues and show signs of metastatic disease or disease that affects organs.

Another thing to do at this point is imaging. Different kinds of tumors require different kinds of imaging to see clearly, but a CT is generally recommended for oral tumors of varying kinds. Imaging is done for two reasons. The first is to look for the size, shape, depth, and extent of the tumor. Some kinds of cancers can spread far beyond and far deeper than they look like they should from their surface appearance. The second reason is to look for signs of metastases throughout the body, which would shift the treatment plan from surgical resection to systemic treatment.

At this point, a biopsy is generally recommended to precisely identify the nature of the tumor. This is done through a histopathological examination of the sample to identify the nature of the cells.

All of this information is put together to identify the tumor and its staging. Staging is a general estimation of how much and how far a cancer has spread, whether it has invaded bone, lymph nodes, or other places of the body, and more. It's critical for determining the ideal treatment plan.

Treatment Options for Oral Tumors in Dogs

The specific treatment plans you develop for dogs with oral tumors will depend heavily on the size, progression, staging, and type of tumor. This is why so much effort goes into the diagnosis; the more information you have, the more accurately you can develop a treatment plan.

Since most forms of treatment are invasive and potentially hard on the patient, the goal of treatment is generally to be as comprehensive as possible while being as conservative as possible. Overdoing treatment can lead to unnecessary side effects, risk, or suffering; underestimating treatment can lead to a tumor coming back.

Treatments generally consist of some or all of these:

  • Surgical resection. For smaller, singular tumors with well-defined margins, low-stage tumors, and many benign tumors, surgical removal is enough. Larger tumors, late-stage tumors, and metastatic tumors may have surgery as part of the solution – if a tumor is blocking function or harming quality of life, for example – but surgery alone isn't enough.

  • Radiation therapy. Radiation can shrink and kill tumor cells, which can make it easier for surgery to remove. Radiation can also help "burn out" the margins of a surgery in cases where simply taking the margins with surgery has worse risks.

  • Chemotherapy. Chemotherapy involves systemic drugs that are targeted at specific cellular pathways. Cancers often have a rapid, ravenous uptake of specific nutrients, and chemotherapy targets those uptake pathways and either poisons them or shuts them down, starving the tumors. The body then absorbs the dead cells and carries them away, shrinking the tumors or clearing them completely.

  • Immunotherapy. The immune system is very powerful and, if it's trained to do so, can recognize abnormal cells and learn to target and remove them. These are potent and specialized treatments still being developed but can be very useful when they work.

  • Targeted Therapy. Targeted therapy based on a genetic analysis of the tumor using FidoCure or Vidium labs has greatly improved survival times for those dogs with malignant oral tumors. These are oral medications that target the mutations that are driving cancer growth and survival.

Armed with the information and diagnosis, you can develop a treatment plan for your patients with oral tumors.

You Don't Have to Go It Alone

Are you a veterinary oncologist? If so, you probably didn't learn anything new from this post. For most vets without a cancer specialty, however, this can demystify the process for you.

Moreover, this can help convince you that it's not just on your shoulders to provide a diagnosis then and there. Veterinary oncologists, specialists, labs, and others are all standing by to support you.

In fact, we're also here to offer our support. As specialists in fields like dermatology, oncology, neurology, and critical care, if you have a case you don't know how to handle, you can call on us, and we'll provide a report to help guide you in developing a plan.

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