Cutaneous histiocytoma in young dogs: operate or wait?
14-month-old Boxer with a solitary 1.5 cm button-like nodule on the pinna, erythematous, hairless and slightly eroded on the surface. It appeared 3 weeks ago and grew quickly.
Cytology shows histiocytic round cells without granules and some small lymphocytes. What is the most appropriate management?
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A. Excision with 3 cm lateral margins and one deep fascial plane
Those are the margins considered for mast cell tumours or sarcomas, not for a benign tumour that usually regresses. On the pinna they would also be very disfiguring.
B. Monitor: it usually regresses within 1–3 months; excise it if it does not, ulcerates or bothers the dog
Correct. Histiocytoma is a benign proliferation of Langerhans cells typical of dogs under 3 years of age. Infiltrating T lymphocytes mediate spontaneous regression (their presence on cytology is a good sign).
C. Oral prednisolone to speed up regression
Regression depends on T lymphocytes; corticosteroids can slow it and are not indicated. Corticosteroids should also never be given for a mass without a clear diagnosis (it could be a mast cell tumour or lymphoma).
D. Full staging (thoracic CT and lymph node aspirates) before deciding
A solitary histiocytoma in a young dog is benign and needs no staging. The diagnosis should be reconsidered with multiple or persistent lesions, or in older dogs.
lightbulb Key takeaway
The head, pinnae and limbs are its typical locations. On cytology, the absence of metachromatic granules distinguishes it from a mast cell tumour. If it does not regress within about 3 months, or the dog is older, excise it and submit it for histopathology to rule out other round cell tumours.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.