Q My dog had a mass removed from the inside of her mouth and it is cancer. What are her chances the finding was malignant melanoma?
A: Unfortunately, the odds are it is a malignant melanoma. Malignant melanoma is the most common oral tumor found in dogs. Overall cancer of the oral cavity is the fourth most common cancer in dogs. This is a time when it is better to be a cat, as dogs get oral tumors 2.5 times more frequently than cats.
These masses are most commonly identified and brought to a veterinarian's attention by the caregiver. However, if located in the back of the oral cavity, the mass itself may not be visible. Symptoms of a mass in the mouth or throat may include increased salivation, which may or may not contain blood, loose teeth, facial swelling, nose bleeds, bad breath, trouble eating or drinking and pain when the mouth is opened.
Oral tumors are similar to any other tumors in that to know a prognosis and plan treatment, we must know what type of tumor it is and if it has spread.
Before any aggressive testing is done, we want to determine, to the best of our ability, if the tumor has spread. Ideally, a small sample from the lymph nodes that drain the tumor should be sampled. This should be done even if they do not feel enlarged. Radiographs of the lungs are taken to insure there is no visible spread (metastasis) to the lungs. Abdominal ultrasound is not a must but often performed in older dogs to make sure there is nothing else going on which could change the plan.
From appearance we can make an educated guess as to the tumor type, but it is still only a guess. Generally a biopsy, the removal of a piece of tissue for a pathologist to look at under a microscope, will be recommended to give us a definitive diagnosis.
For a mass attached by a thin stalk, the whole tumor can be removed at this point. Firmly attached masses should be biopsied first; for certain tumors, the underlying bone may need removal, but this may be too aggressive for a less invasive tumor.
Breeds with a large amount of oral pigment are predisposed to malignant melanomas, such as Cocker spaniels, Rottweilers, chow chows and golden retrievers. Since they originate from pigmented tissue, most (67 percent) will be dark in color. However, around 33 percent are unpigmented, so a pink tumor could still be a melanoma. Tumors of the lips have less potential to spread than those found inside the oral cavity.
Squamous cell carcinomas are the most common oral tumor. Cats that live in smoking households have twice the risk of developing this form of cancer. These tumors are slow to spread, so surgery can provide long-term control. The problem is that for most cats, these tumors are not noticed until they have invaded the bone, making surgery more difficult.
Multiple other tumor types can develop in the oral cavity of dogs and cats. Their tissue of origin and location will often dictate which therapy is recommended. Some are even benign and can be removed with surgery.
Surgery is the best treatment for most oral tumors. When removing a tumor, we not only want to remove the visible mass but normal tissue surrounding it. This is because there are usually tumor cells not visible to the eye in this tissue. If we leave these behind, it will quickly grow back. The problem with oral surgery is that part of the jaw bone must be removed. But dogs and cats adapt well to having a portion of their jaw removed as they do not have the concerns with their appearance that we do with ours; as long as they can eat and drink, they keep on going.
For tumors that cannot be surgically removed, radiation therapy is another option. Radiation is not usually a cure but may slow regrowth. Chemotherapy is not a good primary treatment for oral tumors. It may be used to slow the spread of tumors known to go to lymph nodes or distant tissues.
There is a vaccine being used for the treatment of malignant melanomas in dogs. Unfortunately, it does not prevent the cancer but is used once a diagnosis is made. The vaccine stimulates the dog's immune system to recognize and then destroy the tumor. It is not a cure and usually used in combination with surgery.
Early detection is important as oral tumors are most easily treated when they are small and well-defined. Teaching your pet to allow you to brush its teeth has the added benefit of allowing you to evaluate the area for any masses on a regular basis. During your pet's annual dental exam, their veterinarian can perform a detailed search for any masses, too. If you see anything that worries you, have it checked out.
Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to firstname.lastname@example.org.
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