Laboratory tests to identify concurrent disease
A complete blood count, a serum chemistry profile, urinalysis, and feline leukemia virus and feline immunodeficiency virus
testing are recommended to detect concurrent or paraneoplastic disease. While an infrequent finding in cats with oral squamous
cell carcinoma, hypercalcemia has been reported in cats with this tumor.4,11,12 In a recent study of 71 cats with hypercalcemia, seven had oral squamous cell carcinoma, and six of the seven showed radiographic
evidence of bone lysis.12 Hypercalcemia in these cases is thought to be a direct result of the bone lysis by the local tumor.4,11,12
Figure 6. An intraoral radiograph of a cat with left rostral mandibular squamous cell carcinoma. Note the severe osteolysis;
missing teeth; free-floating, displaced teeth; and periosteal reaction in the affected mandible.
Imaging to determine the extent of invasion
Obtaining intraoral radiographs is critical because many structures overlap within and outside the oral cavity on standard
skull radiographs. Dental radiographs can reveal invasion of underlying bone with sclerotic, periosteal proliferation and
displacement of associated teeth (Figures 6 & 7). Marked osteolysis may also be identified because of tumor invasion and is seen in up to 70% of affected cats.13 Severe osteolysis may result in secondary pathologic mandibular fractures.13 In one study, radiographs demonstrated that osteolysis affected a much greater area than was suspected based only on physical
examination in 46% (24 of 52) of cats. This crucial information led to changes in the treatment plans for these patients.5
Figure 7. An intraoral radiograph of a cat with a maxillary squamous cell carcinoma. Note the marked osteolysis distal to
the maxillary left canine tooth extending around the maxillary left fourth premolar.
Computed tomography is a more sensitive way to define the extent of the tumor before surgery or radiation therapy. Ultrasonography
may also be used to help delineate the soft tissue margins of lingual squamous cell carcinoma.14
Fine-needle aspiration to assess the primary lesion and regional lymph nodes
The primary lesion may be aspirated to provide a rapid preliminary assessment via cytologic examination. If sedation is required
to obtain the aspirate, be prepared to also do an incisional biopsy (see below).
While rare, the most common sites of metastasis for oral squamous cell carcinoma in cats are the mandibular or retropharyngeal
lymph nodes. Regional lymph nodes, whether enlarged or not, need to be assessed via fine-needle aspiration and cytologic examination.
Physical examination alone is a poor indicator of lymph node metastasis. In a study of seven cats and 37 dogs with a variety
of solid tumors, six out of 27 (22%) animals in which lymph nodes were normal-sized or only slightly enlarged had metastatic
disease identified via cytology.15 The sensitivity of cytologic evaluation of fine-needle aspirates was 100% (no false negative results), and the specificity
was 96% (13 of 14 that had cytologic evidence of metastasis to regional lymph nodes also had histologic evidence), signifying
that fine-needle aspiration is a consistent method of assessing the regional lymph nodes.15
Just as normal-sized nodes may contain tumor cells, enlarged nodes may not. In a study of seven cats treated with mandibulectomy
and ipsilateral lymph node excision, two nodes noted to be large and firm on physical examination were histologically free
of tumor cells, while one nonpalpable node had metastasis.4 In another study of 52 cats with oral squamous cell carcinoma, 15 (29%) cats had enlarged regional lymph nodes, but only
seven (13%) of the cats had evidence of squamous cell carcinoma in the node on cytologic examination of a fine-needle aspirate.5 These findings provide further support that physical examination alone is insufficient to determine lymph node status in
these patients and that all locoregional lymph nodes need to be microscopically assessed for metastasis.
Biopsy for definitive diagnosis
Histologic examination of an incisional biopsy sample is required to definitively diagnose feline oral squamous cell carcinoma.
It is important to obtain a large sample since feline oral squamous cell carcinomas are frequently infected, necrotic, or
inflamed. Large samples that include healthy tissue at the edge and also include deeper areas of the lesion will increase
the diagnostic yield. Feline oral squamous cell carcinoma should never be biopsied through the skin but rather through an
intraoral incision. An intraoral biopsy prevents seeding of the tumor into the surrounding normal external tissues; these
tissues are required for local reconstruction after oral tumor excision and, thus, need to be preserved without tumor contamination.2
Table 2 TNM Clinical Staging System for Oral Tumors
Squamous cell carcinoma is usually a straightforward histologic diagnosis. The typical histologic characteristics of squamous
cell carcinoma include irregular cords of pleomorphic epithelial cells with abundant eosinophilic cytoplasm, prominent intercellular
bridges, and keratin pearls.1
Clinical tumor stage can be assessed by using the World Health Organization's TNM (tumor, nodes, metastasis) system (Table 2). The diameter of the primary tumor at its greatest dimension is classified as T1, T2, or T3. Bone invasion (determined radiographically)
is described as either a (absent) or b (present). Regional lymph node involvement is categorized as N0, N1, N2, and N3. Distant metastasis is described as either
M0 (absent) or M1 (present).5