Page 96 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Epithelial Tumours
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Variants
VetBooks.ir Some of the variants listed below can be recognized on cytology (e.g. spindle cell variant) or their
cytological presentation has been described in literature (acantholytic variant). The others
require histopathology for recognition.

• Acantholytic squamous cell carcinoma:
• Cytologically, this variant is characterized by a heterogeneous population of round to
spindle- shaped cells that exfoliate individually or in small clusters.
• Nuclei are round with finely stippled to hyperchromatic chromatin.
• The cytoplasm is amphophilic and finely vacuolated.
• Spindle cell squamous cell carcinoma:
• Rare variant of poorly differentiated SCC.
• Cells vary from polygonal to spindle shaped.
• Spindle-shaped cells have round to oval nuclei and two cytoplasmic tails that project away
from each side of the nucleus.
• The cytoplasm is dense, pale to moderately basophilic and often has well-defined
margins.
• A transition from the spindle-shaped cells and the more classical polygonal cells usually
helps in the diagnosis.
• Verrucous and papillary variants:
• Rare variants.
• Cytologically they are not distinguishable from the more classical form of SCC.

Differential diagnoses
• Keratinizing basal cell carcinoma
• Basosquamous carcinoma
• Papilloma

Pearls and Pitfalls
In cats, a multicentric form of squamous cell carcinoma in situ has been described. The neo-
plastic cells are confined to the epidermis and do not invade through the basement membrane.
This form is characterized by the presence of multifocal plaques or verrucous lesions that can
occur at any site and with no relationship to sun exposure.