Author's note: This is the first of two articles that will address the most common canine and feline oral tumors. This article will discuss
canine melanoma and squamous cell carcinoma. The second article will discuss fibrosarcoma and benign tumors in dogs as well
as SCC and fibrosarcoma in cats.
Photo 1: Dog with an oral melanoma. Note that this tumor is not pigmented.
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Oral tumors are the fourth most common cancer in dogs and represent 6 percent of all canine cancers. The most common malignant
tumors in dogs are melanoma, fibrosarcoma, SCC and osteosarcoma. Benign tumors include the epulides (ossifying, fibromatous
and acanthomatous) and other odontogenic tumors. In cats, oral tumors make up 3 percent of all feline cancers. SCC is the
most common malignant tumor followed by fibrosarcoma. Benign oral tumors are much less common in cats.
Photo 2: At necropsy, this 10-year-old Pug had widespread metastasis including the heart (pictured), as well as the lung and
intestinal tract.
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Unfortunately, due to the location, these tumors are frequently not diagnosed until they are advanced, leading to a poorer
prognosis. Early detection through client education and thorough oral examinations as well as aggressive intervention may
improve the prognosis for our patients.
Canine oral tumors
Photo 3: Metastasis to the adrenal gland.
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Melanomas make up 30 to 40 percent of all oral tumors in dogs. They are typically friable pigmented tumors that occur most
frequently along the gingiva, buccal and labial surface of the lip, on the hard or soft palate, and rarely the tongue (Photo
1). There are some melanomas that do not contain any pigment (amelanotic melanoma) so they may appear as friable fleshy lesions.
Photo 4: Cytology of a dog with oral melanoma. Note that several of the cells contain small pigmented granules, which is consistent
with a melanoma.
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Melanomas in the oral cavity should always be considered malignant regardless of the histology. They are locally invasive,
and bone involvement is not uncommon. Metastasis to the local or regional lymph nodes or lungs is common although patients
can present with widespread metastasis (Photos 2 and 3). It can be difficult to diagnose a melanoma if the cells are poorly
differentiated or amelanotic (Photo 4). Melanomas can be misdiagnosed as round-cell tumors, epithelial tumors or anaplastic
sarcomas. Immunohistochemistry could be helpful in confirming a diagnosis of melanoma although is not infallible. The most
commonly employed markers include S-100 and Melan-A. However, sarcomas can be S-100 positive. The absence of Melan-A still
does not rule out the potential for melanoma. Amelanotic melanomas do not appear to have a more aggressive behavior.
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