Page 198 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Round Cell Tumours
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10.5 Transmissible Venereal Tumour (TVT)
VetBooks.ir Largely benign, contagious venereal neoplasm of probable histiocytic lineage. It is also known as

Sticker’s sarcoma.

Clinical features

• Cutaneous neoplasm occurring in intact stray and wild dogs that exhibit unrestrained
sexual activity. It is transmitted most commonly by coitus.
• It can develop at any age.
• Variably sized, cauliflower-like, pedunculated, nodular, papillary or multilobulated
masses, firm but friable. The surface is often ulcerated and infected.
• Almost always located on the external genitalia; it may also occur in adjacent skin and
oral, nasal and conjunctival mucosae.
• Spontaneous regression within a few months is common.
• Prognosis is generally good. Metastatic spread is occasionally described, in which
case the prognosis is poorer. Metastasis is usually observed in dogs with compromised
immunocompetency.

Cytological features

• Cellularity is variable, often high.
• Background: often basophilic and variably haemodiluted.
• Neoplastic cells are round and discrete with distinct cytoplasmic borders.
• Nuclei are almost perfectly round, paracentral to eccentric, with coarse chromatin. Single
or multiple round nucleoli may be seen.
• The cytoplasm is moderate to abundant and lightly basophilic. It often contains punctate
clear vacuoles. These are often located along the cell borders.
• Cytological features of atypia are variable, up to moderate. They include anisocytosis,
anisokaryosis and presence of mitotic figures.
• Small lymphocytes are often observed in the regressing phase. Reactive fibroblasts associated
with collagen bundles may also be found.
• Neutrophils may be present in ulcerated lesions.

Differential diagnoses
• Other round cell tumours
• Amelanotic melanoma

Pearls and Pitfalls
If the tumour arises deep in the prepuce or vagina, it may be difficult to find without careful
physical examination; this may lead to misdiagnosis if bleeding is confounded with oestrus,
urethritis, cystitis or prostatitis.