Histiocytoma in Dogs

Histiocytoma is a characteristic of a common growth that often appears as a raised, hairless, and red lump on your dog. However, despite it looking “angry” and sometimes even ulcerated, these kinds of growths are usually non-painful and usually go unnoticed by the pet.

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Although histiocytomas are benign and harmless, it’s still recommended to see a veterinarian to get the bump examined. There are various cell growth tumors that can be cancerous , so it’s ideal to make sure the lump isn’t harmful.

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.

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Signs of Histiocytomas in Dogs
Histiocytomas most commonly occur in dogs three years of age and younger.3 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 can be as large as 4 cm in diameter but tend to be less than 2.4

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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).5 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.

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.

Treatment
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.

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.5

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.

Why do puppies get histiocytomas?
Histiocytomas come mostly from genetic factors; there’s nothing you can do to prevent them so just know they are benign.

Do histiocytomas scab when they heal?
Yes, often. As they are going away they begin to look like an ulcer, and then they scab over.
How long do histiocytomas last?
Within two to three months, histiocytomas resolve without issue.

How to Treat Tumors, Growths, and Cysts in Dogs
If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet’s health history, and can make the best recommendations for your pet.