Oral Tumors in Dogs and Cats

Laurie Anne Walden, DVM

Oral tumors are common in dogs and cats. These growths can occur anywhere in the mouth, including the gums, tongue, inner cheek, roof of the mouth, or back of the throat. In dogs, some oral tumors are benign and others are malignant. In cats, most oral tumors are malignant.
 
Malignant oral tumors are very serious and typically have a poor prognosis. The earlier these tumors are found, the easier they are to treat and the better the outcome. Unfortunately, oral tumors are often advanced by the time they’re detected.
 
Signs
Some oral tumors are in a location that’s easy to see while the animal is awake. Others are only found with a full-mouth examination when the animal is under anesthesia, often during a routine dental procedure.
 
These are some of the signs of oral tumors:

• Lump in the mouth or on the lips
• Bad breath
• Excessive drooling
• Difficulty eating or drinking
• Weight loss
• Bleeding from the gums or other part of the mouth
• Pawing at the mouth
• Difficulty opening the mouth
• Swelling or asymmetry of the face
• Tooth loss

 
Benign Tumors (Not Cancer)
Dogs can develop various benign oral tumors. The most common types are acanthomatous ameloblastoma and peripheral odontogenic fibroma. These tumors begin as small pink growths at the gumline next to a tooth. They often enlarge if they’re not removed, and some types invade deeper tissues and destroy the bone around the tooth. Even though these tumors can cause pain and tooth loss, they are considered benign because they don’t spread to other parts of the body.
 
Benign oral tumors are uncommon in cats. A growth in a cat’s mouth is probably malignant.
 
Malignant Tumors (Cancer)
Malignant Melanoma
Malignant melanoma is the most common malignant oral tumor in dogs and is rare in cats. These tumors can be either pigmented (black or brown) or nonpigmented (pink). This aggressive cancer grows quickly and spreads to nearby lymph nodes and more distant parts of the body. In most dogs, malignant melanoma has already spread, or metastasized, by the time it’s diagnosed. The prognosis depends on whether the cancer is detected and treated before it has metastasized.
 
Squamous Cell Carcinoma
Squamous cell carcinoma is the most common oral tumor in cats and the second most common malignant oral tumor in dogs. These tumors are most often located on the gums, the underside of the tongue, or the tonsils but can occur anywhere in the mouth. The tumors are usually not detected until they’re too large to be removed surgically. Squamous cell carcinoma destroys the underlying bone and spreads to nearby lymph nodes. Squamous cell carcinoma has a poor prognosis unless it can be completely removed while the tumor is still small, which is not the case for most cats.
 
Fibrosarcoma
Oral fibrosarcoma is more common in dogs than in cats. This type of cancer destroys nearby tissues but is less likely to metastasize. The prognosis depends on how large and destructive the cancer has become by the time it’s found.
 
Others
Many other cancers can affect dogs’ and cats’ mouths. Some examples are osteosarcoma, mast cell tumor, lymphosarcoma, peripheral nerve sheath tumor, and hemangiosarcoma.
 
Diagnosis
Diagnosis requires tumor biopsy with the patient under anesthesia or deep sedation. Imaging (radiography or computed tomography) is needed to see how deeply the tumor has invaded the surrounding tissues; this is the case for both benign and malignant tumors. Basic laboratory workup (bloodwork and possibly urinalysis) is used to assess the patient’s overall health, especially before anesthesia. Patients with malignant tumors might also undergo tumor staging, which can include more extensive bloodwork and imaging of the chest and abdomen.
 
Treatment
The most effective treatment, when possible, is surgical removal of the tumor and a wide margin of surrounding tissue. “Wide margin” often means removing all or part of the jawbone. Radiation therapy is also used for some patients. Chemotherapy isn’t effective for many kinds of malignant oral tumors. Immunotherapy (a melanoma vaccine) is available for dogs with oral melanoma.