Page 132 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Epithelial Tumours

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8.6 Clear Cell Adnexal Carcinoma (Dog)
VetBooks.ir Adnexal tumour without definitive apocrine, sebaceous or follicular differentiation. It arises in

the dermis and can extend into the subcutaneous adipose tissue.

Clinical features

• Rare tumour described only in dogs.
• Due to the paucity of reported cases in literature, there is no information on age, sex
or breed predisposition and anatomical site predilection.
• Most of the cases described in the literature are slow growing.
• Local recurrence after surgery occurs rarely and metastasis to the draining lymph
nodes is uncommon.

Cytological features
• Cellularity is variable.
• Background: this is one of the most characteristic cytological features of this tumour. It
contains a large amount of lacy, grey to amphophilic to basophilic, amorphous material
representing the cytoplasmic content of the ruptured neoplastic cells. It can be variably
haemodiluted.
• Cells exfoliate individually, in cohesive clusters or loose aggregates.
• Cells are often large. Morphology can vary from polygonal to oval and spindle shaped.
• Nuclei are round, occasionally oval, central and have coarse chromatin. They often contain
one to multiple prominent nucleoli.
• The cytoplasm is variable in amount, often abundant with poorly defined margins. It is
lightly grey-basophilic and may contain eosinophilic stippling, occasionally forming small
needle-shaped pink structures. Cytoplasmic rarefaction can be observed.
• Rarely, the neoplastic cells contain melanin granules.
• Anisokaryosis and anisocytosis are often prominent. Multinucleated cells can be found (up
to 10–15 nuclei).
• Necrosis and calcification might be observed.

Differential diagnoses
• Poorly differentiated sebaceous carcinoma
• Sarcoma (including liposarcoma)
• Balloon cell melanoma

Pearls and Pitfalls
• The name of this tumour derives from the fact that, on histopathology, the cells typically
have a ‘clear’ and vacuolated cytoplasm.
• The misclassification of this tumour in favour of an erroneous diagnosis of sarcoma or mela-
noma can lead to inappropriate case management, as sarcomas and melanomas have a higher
metastatic tendency and may have a worse prognosis.
• In some cases, immunohistochemistry is required for a definitive diagnosis.