Unknown Breed – Canine

Species: Canine
Breed: Unknown
Age: 20M
Gender: Female, Spayed

Source/History: Subcutaneous, firm, 1.1 cm mass below right carpus.

Image 1: Mass aspirate 20X
Image 2: Mass aspirate 50X
Image 3: Mass aspirate 100X
Click here for the IDEXX Pathology Report on this case.

Microscopic Description:

Three slides, one pre-stained are received and evaluated. They range from moderate to high cellularity and consist of superficial squamous epithelial cells in a mild blood background with a possible mild increase in neutrophils with few lymphocytes, monocytes and eosinophils. Squamous epithelial cells have round to angular cell borders, round to oval variably pyknotic nuclei that are occasionally undergoing karyolysis and cytoplasm that is basophilic, often with fine vacuolation, and pink often fibrillar granulation. Mild atypia including anisocytosis, anisokaryosis, occasional binucleation and perinuclear vacuolation is appreciated. No infectious organisms are seen.

Cytologic Interpretation:

Squamous epithelial proliferation with evidence of mild neutrophilic inflammation (please see comments)


The slides are similar with moderate to high cellularity consisting of squamous epithelial cells. The cells are generally nucleated and have bright pink cytoplasmic granulation. Similar cells referred to as koilocyte-like or hypertrophied keratinocytes can be seen with viral papillomas or less commonly squamous papillomas. The cells lack prominent features of malignancy, but other less likely considerations include a well-differentiated squamous cell carcinoma or other follicular/adnexal lesions. Biopsy and histopathology of the lesion is indicated for a definitive diagnosis.

Viral papillomas are generally found in young dogs and are induced by papillomaviruses. These viruses are double-stranded DNA viruses that have a tropism for squamous epithelium. Exophytic  papillomas are found on the face, ears, and extremities while inverted/endophytic papillomas are generally found on the ventrum.  Exophytic papillomas may regress; however, malignant transformation could also rarely occur.

Squamous papillomas occur less commonly than their viral counterparts and are suspected to be of non-neoplastic and possibly traumatic origin. These lesions are often pedunculated and noted on the face and feet.

Reference/Additional Information:

Gross TL, Ihrke PJ, Walder EJ, et al: Skin Diseases of the Dog and Cat, Clinical and Histopathologic Diagnosis. 2nd ed. Oxford UK, Blackwell Science, 2005; pp 567-571.

Moore RM, Libby AL, Khanal S, et al. Is this cell hollow? Yesterday, Today, Tomorrow. Vet Clin Pathol 2016; 45: 8–9.

Sprague W, Thrall MA. Recurrent Skin Mass from the Digit of a Dog
. Vet Clin Pathol 2001; 30:189-192.



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