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Cutaneous Histiocytomas in Dog

"Punch" was a bouncy, exuberant, four-year-old Boxer dog

"Punch" was a bouncy, exuberant, four-year-old Boxer dog.  He was brought into the practice as the owners had noticed the sudden appearance of a red, raised, round, lump on one of his front legs. Punch was not bothered by his lump, he gave it an occasional lick, otherwise he left it alone. It was a lump that had not been noticed before though, and his owners were understandably concerned and wanted to know what this lesion was. 

I advised that this lump was sampled initially using a fine needle biopsy, and the sample was sent to the Laboratory for a Cytological examination.  

The Cytology result came back as a confirmed Cutaneous Histiocytoma.  

A cutaneous histiocytoma in the dog is a common, benign tumour composed of histiocytes. A histiocyte is a cell that is part of the body's immune surveillance system. Histiocytes take up and process foreign antigens, such as pollens and viral, bacterial, and fungal microorganisms. They then they then migrate to the local lymph nodes. Here they present antigens to other immune system cells to stimulate them into a variety of activities to protect the body.  

In their early stages, over the first couple of weeks, Histiocytoma lesions can grow quite rapidly. During this period of rapid growth, they can ulcerate and be self-traumatised, and they may then become secondarily infected. Histiocytomas may then quietly regress and disappear spontaneously over a period of a few weeks. This spontaneous regression is common in these tumours. 

This tumour can occur in any breed of dog, but some breeds appear to be much more susceptible, breeds that may be more at risk include Bulldogs, American Pit Bull Terriers, American Staffordshire Terriers, Scottish Terriers, Greyhounds, Boxers, and Boston Terriers. 

Most commonly, histiocytomas are found in young dogs, although they can occasionally be found in older dogs. Most dogs affected though are less than six years of age, occasionally as young as eight weeks old. They appear as a small, round, solitary, hairless, inflamed lump. They are mostly found on the head, neck, ears, and on the lower limbs, and they are usually less than 2.5 cm in diameter.  

An accurate diagnosis of what the lump is relies upon a microscopic examination of the lump tissue at a Laboratory. Depending on the presentation and location of the lump, your vet may recommend one or more methods of obtaining a tissue sample for a full diagnosis. It is important to sample these lumps as they can look and present similarly to other much more concerning cancerous tumours, so sampling is always advised.  

An initial diagnosis is generally made through Cytological examination of the lesion, this is often used for rapid, preliminary assessment of the lesion. The lump is sampled using a small needle to take some cells. These cells are analysed under a microscope to identify their origin and any indications of any malignancy.  

Sometimes however, it is not always possible to achieve a definitive diagnosis in this way, in which case your vet will recommend removing a larger biopsy sample or removing the whole lump completely for a much fuller tissue analysis by histopathology.  

This is one of the rare types of tumours that the body's own immune system can eventually eliminate. However, lump growth in size, change in structure, ulceration, itching, secondary infection, and bleeding are often problems that then require surgical intervention. If this occurs and the lesion does not spontaneously regress, the treatment then advised is surgical removal of the lump, with histopathology also advised to confirm the diagnosis. Histopathology examination gives an accurate diagnosis, a prediction of the lump’s activity and behaviour and a microscopic assessment of whether the tumour has been fully removed. 

Thankfully, Punch’s lump visibly regressed quickly and resolved spontaneously over a few weeks’ time, and so his Histiocytoma did not require any surgery. Bouncy Punch was then carefully monitored regularly every few months at the practice for any recurrence of his lump, and for any other bumps and lumps. 

Please contact your Vet for an appointment if you are concerned about any lumps you have noticed on your dog’s skin. Not all lumps in dogs are cancerous but having them examined by your vet and appropriately tested is the safest way to monitor any lesions, for your peace of mind, and for the good and long-term health of your beloved pet. 


Alison Laurie-Chalmers, 

Senior Consultant, 

Crown Vets

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