The oral cavity is a common site for neoplasia in cats, accounting for about 10% of all feline tumors.1 The most common malignant oral tumor in cats is squamous cell carcinoma.1 The prognosis for this fast-growing, invasive tumor is grave, so it is vital to identify and treat it early. To help you
manage affected patients, this article focuses on the biologic behavior, pathology, etiology, diagnosis, staging, and treatment
of feline oral squamous cell carcinoma.
Figure 1. The typical appearance of a sublingual squamous cell carcinoma with an irregular and ulcerated proliferative mass.
Oral squamous cell carcinoma is a malignant tumor that may occur anywhere within the oral cavity, is locally invasive, infrequently
metastasizes to ipsilateral regional lymph nodes, and rarely spreads to distant sites.1,2 The most common site of oral squamous cell carcinoma in cats is the sublingual region (Figure 1). The maxillary and mandibular gingivae are also sites of primary tumor development. Infrequently, squamous cell carcinoma
may arise from the tonsillar epithelium.
Figure 2. Note the ulceration and necrosis associated with this sublingual squamous cell carcinoma that eroded through the
dorsal aspect of the tongue.
Mucosal ulceration, necrosis, and severe suppurative inflammation are commonly associated with oral squamous cell carcinoma
(Figure 2). Gross tumor proliferation is often evident in the oral cavity. However, the mucosa can also remain intact over a raised
region caused by squamous cell carcinoma invading into deeper tissues (Figure 3). Cats may present for evaluation of an enlarged jaw, as the tumor can make the mandible look prominent or asymmetrical (Figure 4). Gingival squamous cell carcinoma often invades the underlying mandible or maxilla, leading to severe and extensive tumor
involvement of the bone in that area. Local disease is usually the cause of death.
Figure 3. An intraoral view of a left mandibular squamous cell carcinoma demonstrating the widening of the mandible around
the teeth without an obvious raised and proliferative mucosal lesion.
Oral squamous cell carcinomas grow rapidly. On initial presentation, the tumor is often extremely advanced, resulting in a
grave prognosis. The metastatic rate at diagnosis is low, yet the true metastatic potential is unclear because so few cats
have their local disease controlled to permit long-term follow-up for metastatic disease.2
Figure 4. The same cat as in Figure 3 showing rostral and left mandibular enlargement.
In four studies comprising 81 cats with oral squamous cell carcinoma, 12 cats (14.8%) had documented metastasis to the ipsilateral
submandibular lymph node.3-6 The actual rate of metastasis may have been somewhat higher, as not all cases had cytologic or histologic lymph node evaluation.
In eight cats (10%), metastasis was diagnosed at presentation,3-5 while four cats (5%) developed lymph node metastasis after primary tumor treatment.6 Of these four cats, one was euthanized because of the metastasis; the other three were euthanized because of local tumor
progression.6 Thoracic radiographs were evaluated in three of the studies, comprising 74 cats, and no evidence of thoracic metastasis
was present at initial presentation in any patient.3,5,6 In one cat that had lymph node metastasis, follow-up thoracic radiographs 16 months after treatment showed no evidence
of pulmonary metastatic spread.4 These findings are consistent with the belief that feline maxillofacial squamous cell carcinomas have a low metastatic rate
and that local disease is usually the cause of death.
ETIOLOGY AND RISK FACTORS
The average age of cats with oral squamous cell carcinoma is 12.5 years, with a range of 3 to 21 years. No significant sex
or breed predilection is associated with this tumor. Although several environmental risk factors have been recognized, the
cause of feline oral squamous cell carcinoma remains poorly defined. Various potential contributing factors are discussed
One clinical study found that cats exposed to household environmental tobacco smoke appear to have an increased risk of developing
oral squamous cell carcinoma.7 Cats that had ever lived in a household with a smoker had a nonstatistically significant twofold increase in risk of oral
squamous cell carcinoma compared with cats in nonsmoking households. Cats whose owners reported smoking one to 19 cigarettes
a day had a statistically significant fourfold increase in the risk of oral squamous cell carcinoma compared with cats in
Another study of p53 expression in oral squamous cell carcinoma determined that cats exposed to any environmental tobacco
smoke were four and a half times more likely to overexpress p53 in their tumors than were unexposed cats.8 The p53 protein, the product of a tumor suppressor gene, regulates cell growth and proliferation and prevents unrestrained
cell division after chromosomal damage. Abnormal p53 accumulates in the cell, unlike normal, wild-type p53, and can be detected
via immunohistochemistry. The absence of functional p53 increases the risk of developing various cancers, and it is suggested
that p53 may be a possible site for carcinogen-related mutations within some squamous cell carcinomas.8