What Are Oral Tumors in Dogs?
A oral tumor, also referred to as masses, growths, epulides, cancer or neoplasms, lump and bump is an abnormal growth of tissues that deveoped inside the mouth of dogs. They can occur on the gums, tongue, roof of the mouth (hard and soft palates) and/or back of the throat. Benign oral tumors typically grow slowly by expansion, displacing normal tissue but not invading it. They usually are encapsulated and well-defined. Benign masses are not metastatic; they don’t form secondary tumors in other locations. On the other hand, malignant tumors usually worsen with time and, if not successfully treated, cause serious illness and eventual death.
Oral Tumors in Dogs – Types & Causes
Benign and malignant oral tumors are common in dogs. The mouth is the fourth most common location for canine tumors. They include:
Types of Benign Oral Tumors:
- Epulides - The most common benign tumor of the canine oral cavity. There are several subtypes:
- Fibromatous epulides
- Peripheral odontogenic fibromas (contain bone, dentin or cementum-like tissue within a soft tissue swelling; minimally invasive)
- Acanthomatous ameloblastomas
- Giant cell epulides (giant cell tumor, giant cell granuloma; grow rapidly; involve inflammation and ulceration, bone formation and rapid regrowth after incomplete surgical resection; uncommon in dogs)
- Gingival hyperplasia (abnormal increase in the number of normal cells in a normal arrangement; causes thickening and enlargement of the gums; common in dogs)
- Pyogenic granulomas (usually develop along gum margins; often inflamed and ulcerated)
- Dentigerous cysts (tooth-containing or follicular cycsts; develop around the crown of an unerupted or retained tooth)
- Odontomas (accumulations of normal cells arranged in an abnormal manner; compound odeontomas are hard, tooth-like structures; complex odontomas are hard substances bearing no resemblance to teeth; not considered to be true tumors)
- Papillomas (“warts”; seen mainly in young dogs under 2 years of age; caused by species-specific papillomaviruses)
- Osteomas (slow-growing tumors made of dense, well-differentiated compact bone)
- Plasmacytomas (plasma cell tumors; usually localized, solitary and sessile [attached by a broad base; not pedunculated]; fairly aggressive and can metastasize)
- Amyloid-producing odontogenic tumors (previously called calcifying epithelial odontogenic tumors; can be locally invasive but rarely metastasize; uncommon in dogs)
Types of Malignant Oral Tumors:
- Melanoma (also called melanosarcoma; the most common malignant oral tumor of dogs; seen on gums, lips, tongue and palate; locally invasive and commonly metastasizes to lungs and regional lymph nodes)
- Squamous cell carcinoma (the second most common oral malignancy in dogs; often red, cauliflower-like and ulcerated on the gums and quick to infiltrate bone; masses on tongue or tonsils metastasize most readily)
- Fibrosarcoma (the third most common canine oral tumor; often smooth and firm; rarely breeds)
- Osteosarcoma (bone cancer; affects jaw bones; can bleed)
- Osteochondrosarcoma (multi-lobed tumors of bone and cartilage; locally invasive but slow to spread)
- Mast cell tumor
- Peripheral nerve sheath tumor
- Lymphosarcoma (epitheliotropic lymphoma)
What causes each of these different tumor types is highly variable and often unknown. A genetic predisposition may play a role in canine oral but has not been unequivocally established. Some benign tumors reportedly undergo some degree of malignant transformation, although this too has not been well-documented and appears to be rare
Oral Tumors in Dogs – Symptoms and Signs
Effects of Oral Tumors – From the Dog’s Point of View
Dogs with oral tumors may or may not suffer from discomfort or mechanical difficulties with chewing, drinking and/or swallowing, depending on the nature, location and size of the mass. Most benign oral tumors don’t cause spontaneous bleeding, bad breath (halitosis) or pain, unless they are large enough to become injured by contact with the dog’s teeth. One exception to this is acanthomatous ameloblastomas, which tend to bleed quite a bit. Malignant tumors tend to affect dogs more aggressively and painfully.
Symptoms of Oral Tumors in Dogs – What the Owner Sees
Owners of dogs with oral tumors may notice one or more of the following:
- Focal, localized swelling of the gums (gingiva), tongue, tonsils, roof of the mouth, base of the mouth, back of the throat, muzzle or face.
- Raised mass or masses emanating from the gums (gingiva), tongue, tonsils, roof of the mouth, base of the mouth or back of the throat (may be pigmented/dark or non-pigmented/pink, smooth or rough/cauliflower-like, irregular or rounded; pedunculated [attached to normal tissue by a stalk or stem-like structure) or sessile [attached to normal tissue by a broad base], lobulated or solitary, bleeding or not, firm or squishy).
- Bleeding is uncommon from benign oral masses but can happen. Bleeding is much more common from malignant tumors.
- Disfigurement of the oral cavity if the tumors are locally invasive and invade the lower (mandible) or upper (maxilla) jaw bones.
- Displaced teeth (may remain firmly seated to underlying bone).
- Foul odor coming from the mouth (bad breath; halitosis; most common with malignancies).
- Difficulty swallowing (dysphagia; if the mass is large enough to physically interfere with masticatory [chewing and swallowing] function).
- Excessive drooling (ptyalism).
- Swelling of the lower (mandible) or upper (maxilla) jaw bones.
- Appetite may or may not be affected/reduced (depends on pain).
- Activity level may or may not be affected/reduced (depends on pain).
- Weight loss.
- Tooth occlusion (bite) abnormalities.
- Abnormal facial symmetry.
- Tooth loss.
Dogs at Increased Risk of Oral Tumors
Tumors arising from tooth-forming tissues (called “odontogenic” tumors), and oral papillomas, are more prevalent in young dogs but can occur at any age. Peripheral odontogenic fibromas are seen more commonly in brachycephalic breeds – those with broad skulls, flat faces and short wide heads, such as Boxers, English Bulldogs, French Bulldogs, King Charles Cavalier Spaniels, Pekingese and Pugs. Malignant oral tumors can happen at any age but are more prevalent in middle-aged and older animals. Dogs over 10 years of age are overrepresented among the population of canines with melanoma, especially if they have darkly-pigmented oral mucosa. Cocker Spaniels, Chow Chows, and German Shepherd Dogs are also overrepresented. Adolescents and young adults are predisposed to developing oral squamous cell carcinoma, as are large and giant-breed dogs. Squamous cell carcinoma of the tonsils reportedly occurs 10 times more frequently in dogs living in urban rather than rural environments. Fibrosarcomas and melanomas seem to affect the mouths of large, older males disproportionately, while females are more commonly affected with osteosarcomas.
Oral Tumors in Dogs – Diagnosis and Test
Many canine oral tumors – especially benign ones – are found incidentally by the owner during in-home dental care, by the dog’s veterinarian during a routine annual physical examination and check-up or by a veterinary technician during a professional dental exam and cleaning. Once oral masses are identified, there are a number of different techniques available to diagnose the exact type of cells that they are made of. This usually follows a thorough examination of the oral cavity conducted under heavy sedation or general anesthesia. The results of routine blood work (a complete blood count and serum biochemistry profile) and urinalyses are usually unremarkable and not diagnostic of oral tumor origin.
The main tools used to diagnose oral tumors are radiographic imaging (X-rays), computed tomography (CT or CAT scan), magnetic resonance imaging (MRI), fine needle aspiration, deep tissue incisional or wedge biopsy and/or surgical tumor removal (also referred to as an excisional biopsy). Enlarged lymph nodes can also be taken out surgically and evaluated for evidence of metastasis.
X-rays are used to assess whether malignant oral masses have spread to remote locations, especially to the lungs. Denhtal X-rays can reveal associated dental changes and tumor invasion of the jaw bones. CT scans and MRIs are helpful to define the location and extent of the tumor. An MRI is probably the best tool for assessing tumor size and invasiveness into nearby structures. CT scans give better visualization of calcification and erosion of the cortex (outer layer) of affected bones. However, CT and MRI procedures usually are only available at veterinary teaching hospitals and specialized referral centers, and they tend to be quite expensive.
Fine needle aspiration is a simple in-clinic procedure. The veterinarian inserts a sterile needle into the tumor and draws back on the plunger of the syringe that is attached to that needle. The sample contents are then expressed (squirted) onto a glass slide and examined under a microscope. Normally, cells and fluids are collected. Cancer cells of different types have unique appearances microscopically. However, sometimes not enough cells are aspirated to allow a definitive diagnosis, and many oral masses don’t exfoliate, or shed, cells easily. The more reliable way to evaluate oral tumors is to take actual tissue biopsies from the masses – this involves more than just sampling cells. The veterinarian will cut into the tumor or tumors and remove one or more chunks of tissue. This is called an incisional biopsy. While the entire tumor may be able to be surgically removed (this called an excisional biopsy), many veterinarians prefer to first take incisional biopsies, so that they and the owner have complete and accurate information upon which to make about the best course of treatment. In either case, the biopsy samples will be sent to a pathology library to be evaluated in great detail through a process known as histology or histopathology. The lab report hopefully will tell the veterinarian exactly what kind of tumor is involved, which will guide her treatment recommendations and decisions.
Oral Tumors in Dogs – Treatment and Prognosis
Goals of Treating Oral Tumors in Dogs
The goals of treating oral tumors in pet dogs are to prevent or reduce the rate of growth and/or spread to other locations, prevent or stop invasion of tumor tissue into adjacent structures, relieve pain and discomfort and restore normal mechanical function of the mouth and jaws (including pain-free chewing and swallowing)
The selection of a treatment plan will depend on a number of things, including the tumor type, location, size and malignancy. The dog’s age and overall health, as well as the owner’s finances and commitment to treatment, are very important. The veterinarian’s training, experience and comfort-level treating oral tumors will also play a role. Benign oral masses usually can be treated or at least well-managed by surgical removal. It is important to excise a small amount of normal tissue around the entire mass to prevent local recurrence or regrowth (this is called “getting clean surgical margins”). If teeth are affected, they may need to be extracted. If surgery is not a possible or realistic option, radiation therapy can be used to try and slow tumor growth and relieve discomfort. Fortunately, most benign oral tumors respond well to surgery and/or radiation therapy. Intralesional chemotherapy has also been used to treat certain benign oral tumors in dogs. This involves injecting strong chemotherapeutic drugs directly into the mass in an attempt to destroy the abnormal, rapidly growing tumor cells. Systemic chemotherapy can be helpful as an adjunct to other treatments but rarely is successful on its own in eliminating oral tumors. Oral and injectable pain medications, called “analgesics,” can be prescribed, as can anti-inflammatory drugs, to help relieve discomfort.
Malignant oral masses are more difficult to treat, because they usually grow rapidly, are aggressively invasive and tend to metastasize to remote sites. Just debulking them is rarely helpful. Once the type of malignancy is determined, the entire tumor and a wide margin of unaffected tissue all the way around it should be taken out surgically to prevent re-growth, infiltration and spread. Radiation and/or chemotherapy may help, depending on the type of malignant mass involved. Areas of the mouth that are irradiated tend not to heal normally if subsequent surgery is performed in the same vicinity. Immunotherapy and a commercially available melanoma vaccine for dogs both show promise. Dietary changes, including switching from dry kibble to softer canned food, may be appropriate. Most general practitioners will refer owners of dogs with malignant oral tumors to a board certified veterinary oncologist to handle treatment recommendations and implementation.
Prognosis and Outlook
The outlook for dogs with benign oral tumors is very good to excellent, as long as the tumors can be removed or respond well to radiation therapy. Dogs with malignant oral masses usually have a more guarded long-term prognosis, although if the masses haven’t spread and are completely excised with wide clean surgical margins, the dog can be cured. Oral surgery causes a significant amount of bleeding, which may necessitate a blood or plasma transfusion. This is especially true if it is necessary to perform a mandibulectomy or maxillectomy, which is removal of all or part of the lower or upper jaw bones.