Histiocytoma in Dogs, Symptoms and Treatment

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dog looking sad
Dog Looking Sad

You are relaxing at home with your dog, and you feel a raised, hairless, red growth that seems to have appeared out of nowhere. Seeing a lump on your dog is never a good thing and can be alarming. However, now that you have noted it, you can let your veterinarian know.

A lot of owners of young adult dogs may find a small, hairless, red lump on their dog that wasn't there the day before. This is very characteristic of a common growth called a histiocytoma. Despite looking 'angry' and sometimes even ulcerated, these kinds of growths are usually non-painful and usually go unnoticed by the pet.

What Is a Histiocytoma?

A histiocytoma is a type of benign, or non-cancerous, growth typically seen in young dogs. They classically present as small, hairless, raised red lumps that seemingly pop up out of nowhere. They originate in the Langerhans cells (also called histiocytes), which are part of a dog's immune system to protect against foreign 'invaders' on the skin such as pollen, bacteria, etc. It is not uncommon for them to resolve on their own. Histiocytomas can occur in any breed of dog, but some breeds that they are more commonly seen in include boxers, bulldogs, and Flat coated retrievers.

Signs of Histiocytomas in Dogs

Histiocytomas most commonly occur in dogs three years of age and younger. They are raised and usually smooth-surfaced, giving them a button-like appearance. They typically present on the head, neck, ears, or limbs of a dog but can appear elsewhere. They also tend to be less than 2.5 cm in diameter.

Are Histiocytomas Cancerous?

While histiocytomas themselves are non-cancerous, on a microscopic level, they belong to a broader classification of growths known as round cell tumors. Histiocytomas are not a dangerous type of growth for your dog to get, but there are some varieties of round cell tumors that are malignant (cancerous). As with any new growth or lump you find on your dog, a trip to the vet to have it checked over is needed to ensure that it isn't something more serious.

selective focus photography of tan Labradoodle
selective focus photography of tan Labradoodle

How to Diagnose a Histiocytoma

If your dog suddenly develops a lump or you suspect your dog may have a histiocytoma, it’s important to see a veterinarian.

Your veterinarian will start by performing a thorough exam and obtaining a history on your dog.

As with all growths, definitive diagnoses of the type of growth is done by looking at the cells microscopically. This is accomplished either by surgically removing the growth and biopsying it or performing something called a fine needle aspirate, or FNA. An FNA is performed by collecting cells from the growth on a needle and then transferring them to a slide to look at under the microscope. It is minimally invasive and can be done the same day as your initial exam for the growth. If the growth is located in an area that would make aspirating or biopsying difficult and there is a high suspicion for a histiocytoma, your vet may opt to wait on performing any diagnostics and watch the lump instead to see if they resolve on their own.


Once your vet has definitively diagnosed your dog's new lump as being a histiocytoma, they can then discuss with you removal options. Your vet may opt to wait and see what the growth does in the next few months. If after three months it is still there, your vet may recommend surgical removal. If your dog's histiocytoma is small enough and if your vet office has the capability, your vet may opt to remove your dog's histiocytoma through cryosurgery. This involves a local anesthetic to the area and freezing the growth off. If your dog's histiocytoma is on the larger size, cryosurgery may be less of an option and your dog might need to have it surgically removed with a scalpel and suture.

brown and white dog sitting on green grass
brown and white dog sitting on green grass
brown and white long coated dog lying on green grass during daytime
brown and white long coated dog lying on green grass during daytime

How to Care for a Dog with a Histiocytoma

Although these types of growths are rarely painful or irritating to a dog, it is important to prevent them from licking, chewing, or scratching at it as that can further irritate it and create secondary infections.

If your dog has a histiocytoma surgically removed, as with all post-surgery care, it is of the utmost importance to prevent your dog from licking, chewing, or scratching at the incision to prevent him/her from opening up the incision and/or creating a secondary infection. Your vet will provide specific post-surgery instructions to keep the incision area clean. If you notice any significant redness, swelling, missing stitches, or if the incision feels warmer than the surrounding tissue, be sure to notify your vet immediately.

Do Histiocytomas Provide any Risk to Humans or Other Pets?

Histiocytomas are not contagious and cannot be spread through skin to skin contact. They do not pose any threat to any humans or any other animals that your dog may come into contact with.

If you suspect your dog to have a histiocytoma, it is best to schedule an exam with your veterinarian so that they can provide you with a diagnosis and a treatment plan that best suits you and your dog.

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