Page 95 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Squamous cell carcinoma (SCC)
VetBooks.ir Malignant tumour arising in the epidermis, with cells showing a variable degree of differentiation
to keratinocytes.

Clinical features
• Common tumour in domestic animals. It accounts for approximately 5% of the
skin tumours in dogs and 15% in cats.
• Age: 6–13 years in dogs and 9–14 years in cats.
• Usually solitary lesion, but multiple SCCs can occur. Masses are often alopecic, ery-
thematous and ulcerated.
• Preferred anatomical sites:
• Dogs: nail bed, scrotum, lips, ventral trunk and legs.
• Cats: nasal planum, eyelids and pinnae.
• In cats, predisposing factors include chronic sun exposure (solar-induced form), light
pigmentation of the skin and lack of hair.
• Cutaneous SCC is locally invasive and destructive but generally with a low meta-
static rate. The highest metastatic tendency is observed in digit SCC in dogs.
• Metastases usually occur to the draining lymph node and rarely to other organs.

Cytological features
• Cellularity is variable, generally medium-high.
• Background: variably haemodiluted, pale basophilic and finely granular (proteinaceous).
• The aspirates are composed of numerous squamous epithelial cells at variable degrees of dif-
ferentiation.
• Well-differentiated SCC exfoliates polygonal squamous epithelial cells with a relatively low
N:C ratio and heavy cytoplasmic keratinization. These cells usually occur individually or in
groups. Bizarre cells can be present.
• Nuclei are round, central to paracentral. The chromatin is clumped or coarsely stippled.
Nucleoli are usually poorly visible.
• The cytoplasm is moderate to abundant, dense, pale to moderately basophilic, with angular
borders. It occasionally contains small, clear vacuoles in the perinuclear area.
• Asynchronous nuclear to cytoplasmic maturation can be observed.
• Poorly differentiated SCC usually exfoliates a population of squamous epithelial cells that
are less keratinized. Neoplastic cells are cuboidal and have a high N:C ratio. They are often
in cohesive clusters, which may be disorganized. Cell crowding and nuclear moulding can
be observed.
• Nuclei are round, central to paracentral. The chromatin is finely clumped to coarsely
stippled and multiple prominent nucleoli are often seen.
• The cytoplasm is scant to moderate, moderately basophilic.
• Mitoses may be found.
• Irregularly shaped cells may be observed (e.g. tadpole cells).
• A prominent neutrophilic inflammation is often present, as a result of the ulceration that
frequently accompanies these lesions.
• Neutrophils can be found within the cytoplasm of the neoplastic cells. This phenomenon is
known as emperipolesis.