What Is a Histiocytoma?

A histiocytoma is a benign (non-cancerous) skin tumour commonly seen in young dogs, typically under three years of age. It arises from a type of immune cell called a Langerhans cell, which normally helps protect the skin from infection.

These growths are not contagious and not cancerous, although they can sometimes look alarming to owners.

Typical Appearance

The normal appearance of histiocytomas in young dogs include the following features:

• Usually appear as a small, round, raised lump on the skin

• Often pink to red in colour and smooth or hairless on the surface
• May look ulcerated, crusty or sore, especially if the dog licks or scratches at it
• Generally firm to the touch but not painful

Histiocytomas often grow rapidly over a few weeks before stabilising. They may shrink and disappear on their own within 1–3 months.

Common Locations

Histiocytomas can appear anywhere on the body, but are most frequently found on:

• The head and face (especially ears and muzzle)
• The limbs and feet
• Occasionally on the trunk or neck

They can occur singly, but some dogs may develop multiple lesions at once.

Diagnosis

Although histiocytomas are benign, they can resemble other types of skin lumps, some of which may be more serious. For this reason, your veterinarian will often recommend diagnostic testing such as:

• Fine Needle Aspirate (FNA): Collects cells from the lump for examination under a microscope
• Biopsy or Surgical Removal: Occasionally required if the diagnosis is uncertain or if the lesion does not regress

Microscopic examination confirms whether the lump is indeed a histiocytoma and rules out other possibilities such as mast cell tumours or infections.

Treatment and Management

Most histiocytomas do not require treatment and will regress spontaneously within a few months. However, veterinary monitoring is important to ensure it behaves as expected.

Treatment may be recommended if:

• The lump becomes ulcerated, infected or irritated
• The dog licks or chews at it excessively
• The histiocytoma does not regress within 2–3 months
• Diagnostic tests suggest a different type of growth

In these cases, surgical removal may be performed, both to confirm the diagnosis and to prevent self-trauma or infection.

Your vet may also prescribe anti-inflammatory medication or an Elizabethan collar to reduce irritation and protect the area while it heals.

Prognosis

The prognosis for histiocytomas is excellent. Once removed or resolved, they rarely recur in the same location. Some dogs may develop others in the future, but this is uncommon.

When to Seek Veterinary Attention

You should have any new lump checked by your vet, especially if:

• It is growing quickly
• Your dog is licking, scratching or bleeding from it
• It shows no sign of improvement after a few weeks
• Your dog is older, as other tumour types are more common in mature dogs