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Types of Mouth Cancer in Dogs

Mouth Cancers in Dogs

The types of mouth cancer in dogs vary and it's important to recognize their early signs as soon as possible. Life expectancy in dogs with mouth cancer is better when the growth is discovered early, when it's still small and quick intervention is taken. Dog owners should routinely inspect their dog's mouth, and one of the best times to do this is when the dog's teeth are brushed. There are three types of mouth cancer in dogs that are particularly worrisome, and therefore, any suspicious growths in a dog's mouth should be evaluated by the vet as soon as possible.

 Picture of oral melanoma in dog

Picture of oral melanoma in dog

Oral Melanoma in Dogs 

Among the types of mouth cancer in dogs, oral melanoma is the most common (30 to 40 percent). The term melanoma is used to depict a cancer that develops from special pigment-containing cells known as melanocytes. Dogs with a genetic predisposition for having black pigment in their mouths (chow-chows) are particularly predisposed.

What do oral melanomas in dogs generally look like? Oral melanomas in dogs appear as a black mass (about 2/3 of melanomas are pigmented); however, this is not a general rule, there are melanomas that are not pigmented and these are known as amelanotic. These cancers tend to grow on the dog's gums or the inside lining of the cheeks and floor of the mouth, but they can also be found on the lips, roof of the mouth and under the tongue.

This cancer (in 80 percent of cases) tends to spread to far locations often spreading to the dog's lymph nodes (possibly causing swellings under the lower jaw or in front of the shoulders) and lungs (possibly causing lethargy and coughing). Sadly, by the time oral melanomas are discovered, in most cases they have already spread. Life expectancy for dogs with oral melanoma may depend on several factors.

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One factor is size. According to board-certified veterinary surgeon Dr. David A. Degner, if the oral melanoma is less than 2 cm (0.78 inches) in size, the median survival time is 511 days, but if it's greater than 2 cm, then the survival time is only 164 days. Prognosis is also much better if the cancer is discovered when it's still localized to the jaw bone (this can be seen with x-rays), while the prognosis is poor by the time it has spread to the lymph nodes and lungs.

Left untreated, average survival time of dogs with oral melanoma is 65 days. Treatment consists of surgery, radiation and chemotherapy.

Squamous Cell Carcinoma in Dogs

 Picture of squamous cell melanoma in dog.

Picture of squamous cell melanoma in dog.

Squamous cell carcinoma is the second most common type of mouthcancer in dogs (17 to 25 percent) This cancer develops from the abnormal growth of squamous cells, which are found in the skin’s upper layers.

What do these cancers generally look like? First of all, they have a tendency to show up in the gums nearby the canine teeth, however, they can also show up on the tonsils (tonsillar squamous cell carcinoma) and tongue (lingual squamous cell carcinoma). When it comes to appearance, these growths may show areas of ulceration. Affected dogs may also develop secondary signs such as facial swelling, excessive drooling, trouble eating, pain upon opening the mouth and bad breath.

Life expectancy for this type of oral cancer in dogs once again depends on several factors. Location of the tumor is one of them. If the cancer is found in the front of the mouth the prognosis is far better than if it's found in the back of the dog's mouth or if it affects the dog's tongue or tonsils. Treatment consists of surgery, radiation therapy, or a combination of both.

Oral Fibrosarcomas in Dogs 

picture of dog oral fibrosarcoma

Picture of oral fibrosarcoma in dog

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Oral fibrosarcomas are the third type of mouth cancer in dogs (it affects 8 to 25 percent of dogs). These cancers develop from the fibrous connective tissue in the mouth. While this form of cancer can affect any breed, Golden retrievers are particularly predisposed.

What do oral fibrosarcomas in dogs look like? Typically, the growths are the same color of gum tissue (non-pigmented) and may be with or without ulceration. They are quite proliferative tumors. They may also feel hard to the touch, adds veterinarians Dr. Scott.

While these cancers are locally invasive, the good news is that they tend to have a low metastatic rate, with the chances of them spreading to distant body parts being around 10 to 20 percent. Median survival time with surgery and radiation is around 1 to 2 years, according to Dr. Degner.

Treatment consists of surgery to remove the growth. Depending upon its location, the surgery may involve partial removal of the jaw bones. Radiation therapy may be beneficial to kill any roots of the growth that may have been left behind.

Other Types of Mouth Cancer in Dogs

The tissue sample taken from the liver is checked under a microscope.

A pathologist looks at biopsied tissue under a microscope.

While the above are the most common types of mouth tumors in dogs, there are several other types of mouth cancer in dogs; however, they tend to be less common. These other types of mouth cancer in dogs include osteosarcoma, chondrosarcoma, mast cell tumor, lymphoma, hemangiosarcoma, plasma cell tumor, and multi-lobular tumor of bone.

Of course, not all of growths in a dog's mouth are malignant, there are several benign growths such as gingival hyperplasia, canine warts, ameloblastoma and canine epulis.

As seen, there are several types of tumors in dogs and they can be benign or malignant. For this reason, any new growth or lump in a dog's mouth should be checked by a vet.

Visual inspection of the growth is not sufficient to know exactly what it is, the only way to know for sure what a growth in a dog's mouth exactly is through a biopsy sent off to a pathologist for evaluation.

"The classic expression “Just watch it” has been dubbed the three deadliest words in veterinary medicine."~Veterinary Practice News 

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  • Blue Pearl: Oral Melanoma in Dogs
  • DVM360: Finding and treating oral melanoma, squamous cell carcinoma, and fibrosarcoma in dogs
  • Hoyt RF, Withrow SJ. Oral malignancy in the dog. J Am Anim Hosp Assoc. 1984;20:83–92

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