What is Histiocytoma in dogs
Histiocytoma is a type of benign skin tumour that tends to arise on the skin of young dogs. While young dogs (under three years of age) are more likely to develop these types of tumours (especially on the face and extremities), histiocytoma in dogs can happen at any age, in any location. These masses are benign and generally will resolve if left untreated, within two to three months or less.
The exact underlying cause isn’t fully understood. Histiocytomas are made up of a special type of immune cell, and it is likely that an inability to regulate within the immune system plays a role in their development.
There may also be a genetic component because several breeds have a higher risk of developing histiocytomas. This type of tumour can occur in any breed, but some breeds appear to be more susceptible, including Boxers, Great Danes and Dachshunds.
Written by Dr. Mariella Roberts, Veterinary Surgeon, Animal Trust Vets CIC | Published April 2025 | Review date April 2027 | This advice is for UK pets only and is not a replacement for seeing a vet
Symptoms
Dogs with histiocytomas may experience the following:
Hairless, raised, red skin bump
Bleeding from the lump
Itching
Open sore with pus (if infected)
Swelling around lump (if infected)
When to contact your vet
It’s best to have your vet check for any lumps on your dog so they can advise you on what to monitor, or if testing is necessary.
In addition, if you notice any of the following in a pre-existing lump:
The lump becomes irregular in shape or texture
The skin over or around the lump becomes red or black
The lump starts growing rapidly or swelling develops around it
Your dog starts paying attention to the lump
There is discharge coming from the lump
Diagnosis
Unfortunately it is not possible to diagnose a histiocytoma from examination alone and histiocytomas can have a similar appearance to other types of skin tumour.
Your vet might suggest considering investigations such as:
FNA (fine needle aspirate) which consists in gently inserting a needle into the skin mass to collect a sample of cells. This sample is placed onto a glass slide, stained, and then viewed under a microscope to identify the type of cells present.
Biopsy, a small portion of the mass (or the entire mass) is removed and sent to a laboratory for testing.
Treatment
In most cases, histiocytomas in dogs generally don’t require treatment. They usually regress on their own within two to three months, as the immune system controls their growth.
If the histiocytoma is in an area with frequent contact, or your dog repeatedly licks or scratches it, it may bleed and ultimately become infected. This is quite common for histiocytomas on a dog’s paw. In these cases, creams or other medications may be used to help to resolve the issue.
If the histiocytoma doesn’t regress or causes discomfort, surgical removal may be recommended by your vet for a permanent solution.
Prevention
Because it’s not fully understood what causes histiocytomas, it’s difficult to determine the best prevention strategies.
However, because histiocytomas are generally not harmful to a dog’s health, pet owners can focus on preventing irritation and infection while waiting for them to regress. This can be done through close monitoring and promptly bringing up any concerns to your vet.
Outlook
The outlook for histiocytomas of the skin is usually excellent as most of them will resolve on their own, or be completely cured by removing surgically, with a very small percentage (less than 1%) potentially growing back.