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Canine cutaneous histiocytoma is a common, usually benign tumour of dogs. It is thought to be derived from epidermal Langerhans cells.

These tumours are seen mostly in younger dogs, and the incidence drops drastically after 3 years of age. There are no apparent breed or sex predilections.

Clinical Signs

Histiocytomas generally arise on the head, ears and limbs of dogs, and appear as rapidly-growing, erythematous, dome-shaped nodules less than 2.5cm in diameter. They are usually solitary, though multiple lesions can appear in a short period of time.

Alopecia and ulceration are common.

Lymphadenopathy can occur due to migration of histiocytoma cells to the draining lymph nodes.


A cytology sample should be taken by fine needle aspiration. A cytological diagnosis is not always easy to make for these tumours, and they can be confused with granulomatous inflammation, mast cell tumors, plasmacytomas, and cutaneous lymphosarcomas.

On cytology: the cells appear round, with moderate anisocytosis and anisokaryosis. Nucleoli may vary from inconspicuous to prominent.


The tumour should be considered benign, and in the majority of cases will resolve spontaneously within 2-3 months without treatment.

If present, the lymphadenopathy will usually regress at the same time as the lesion.

Surgical excision can also be an option if the mass does not regress or it causes bleeding or discomfort to the animal.

Histiocytoma Learning Resources
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Cytology Q&A 09


Merck and Co (2008) Merck Veterinary Manual Merial

Gross, T. (2005) Skin diseases of the dog and cat Wiley-Blackwell

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