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In dogs, about half of all oral tumors are malignant, meaning they can metastasize (spread to other parts of the body), and half are "benign", meaning they do not metastasize. Some of the "benign" tumors are locally destructive and aggressive, so we prefer to use the term "non-malignant" instead of benign.
Common malignant oral tumors in dogs:
- Malignant melanoma
- Malignant melanoma is the most common oral tumor in dogs. Small breeds and male dogs are predisposed. Melanoma can appear as a mass, an ulcer, or simply an area of pigmented tissue that is not raised or ulcerated. It is an aggressive cancer that can rapidly grow and invade structures around the mouth, and easily spreads to other areas of the body. If the tumor is diagnosed at an early stage, when it is small and has not metastasized, it may be cured with complete excision of the tumor and at least 1cm of surrounding tissue, including bone. For large tumors or those in areas that are not surgically treatable, radiation therapy may help shrink the tumor, but will not stop it from metastasizing, and most dogs will die of tumor spread within four to six months. There is a melanoma vaccine available that may help some patients after surgical removal of the tumor.
- Squamous cell carcinoma (SCC)
- Oral SCC is an aggressive cancer that destroys bone, but is relatively slow to metastasize, so if it is detected when the tumor is small, surgery can be curative. Surgery involves removing the tumor and at least 1cm of the surrounding tissue, including bone. Typical survival time following surgery is 18-26 months. Although radiation therapy is also an option, the median survival time following RT is only 10 months. Papillary SCC, which occurs in young dogs, does not metastasize and is considered surgically curable.
- Oral fibrosarcomas in dogs are locally aggressive, but only about 1/3 of cases metastasize (usually to the lungs). Surgical cure requires removal of the tumor and at least 2cm of surrounding tissue. There is a variant called biologically high-grade, histologically low-grade fibrosarcoma which grows rapidly but may appear to be a benign "fibromatous epulis" (see below) on initial biopsy. These tumors are difficult to cure with surgery alone, but surgery followed by radiation therapy may be successful.
- Osteosarcoma of the upper jaw metastasizes in 50% of patients, while on the lower jaw it is about 28%. However, osteosarcoma of the jaws is less likely to metastasize than the limbs, and surgery (removal of the tumor and at least 1cm of surrounding tissue, including bone) is sometimes curative. Approximately 70% of patients treated with surgery will live 1 year or more after surgery.
- Extramedullary plasmacytoma (EMP)
- In the largest published study on canine oral EMP, median survival time was only 90 days for dogs who did not receive treatment or with incomplete surgical removal and no adjuvant therapy (Wright ZM, Rogers KS, Mansell J; Survival Data for Canine Oral Extramedullary Plasmacytomas: A Retrospective Analysis (1996-2006); JAAHA 2008; 44:75-81).
Common non-malignant oral tumors in dogs:
- Canine Acanthomatous ameloblastoma (CAA, aka "acanthomatous epulis")
- CAA is a benign but locally aggressive tumor which originates from normally dormant ameloblasts (epithelial cells that produce enamel during tooth development) in the gingiva and periodontal ligament. Curative treatment involves excision of the tumor and at least 0.5-1.0cm of surrounding tissue, including bone.
- Peripheral odontogenic fibroma (POF, aka "fibromatous epulis" or "ossifying epulis")
- POF are benign, slowly growing tumors that originate in the gingiva from dormant cells of the tooth-forming apparatus. They often produce bone. Excising the mass may be curative, or the POF may regrow slowly. Complete cure requires en bloc resection (including the tooth and surrounding bone associated with the POF). Because these are slowly growing, non-destructive and non-painful, we often choose periodic excision rather than en bloc resection if the POF is at a structurally or functionally important tooth.
In cats, nearly all oral tumors are malignant, and very few are surgically curable. The most common oral tumor in cats is squamous cell carcinoma, which has a grave prognosis: the median survival time is 2 months. Fibrosarcoma, osteosarcoma, and melanoma are less common, and may be surgically treatable if detected at a very early stage.