What Is a Histiocytoma?

Histiocytoma in a dog © Lianne McLeod DVM
Lianne McLeod DVM

A histiocytoma is a benign (non-cancerous) skin tumor, usually seen in young dogs, that often spontaneously regresses without treatment. It is a common tumor that can occur in any dog breed. Some dog breeds, however, such as boxers, bulldogs, greyhounds, and bull terriers seem to be more susceptible to histiocytomas. 

What Does a Histiocytoma Look Like?

The appearance of a raised, hairless and bright red "angry" looking skin lump on a young dog is characteristic of a histiocytoma. This is often alarming to dog owners, as these lumps often appear suddenly, almost overnight. Histiocytomas are not painful, and most dogs do not even seem to notice them, despite the fact that they lump may be ulcerated. It is unusual for more than one tumor to be present at once. 

Where Do Histiocytomas Appear? 

Histiocytomas generally appear on dogs younger than three years old. The tumors have a button-like appearance and they are most often found on the head, neck, ears, and limbs (though they can appear in other places). Histiocytomas tend to be less than 2.5 cm in diameter. 

Are Histiocytomas Cancerous? 

Histiocytomas are classified microscopically as a round cell tumor, but unlike cancers, they do not grow and are not dangerous to your pet. There are, however, a variety of tumors included in the round cell tumor classification, so it is important to have your dog seen by a vet. While histiocytomas are benign, other tumors in this class may be more serious. It is important to have your veterinarian check out any new lumps and bumps on your pet to be sure.

How Are Histiocytomas Diagnosed?

Definitive diagnosis is established by examining the tumor cells microscopically through cytology or biopsy. Your veterinarian may want to wait and watch the lump, based on the age of your dog and the location and presentation of the lesion. Histiocytomas can often spontaneously regress in 2-3 months. If in doubt, a biopsy will provide an answer as to the nature of the lesion.

How to Care for a Dog With Histiocytomas

Depending on the location of the histiocytoma, a dog may not even be aware of the tumor. Regardless, it is important to prevent your dog from licking, scratching, or biting the tumor. This will help prevent inflammation, infection, and bleeding. 

If a histiocytoma has been surgically removed, it's important for the incision site to remain clean and dry and prevent any rubbing, licking, biting, or scratching at the site. Your veterinarian will provide post-surgery directions on how to care for the wound. Be sure to let your veterinarian know if there is any significant swelling, bleeding, or open stitches. 

Do Histiocytomas Provide Any Risk to Humans or Other Pets?

There are no risks to people or other pets from histiocytomas. They are not contagious and cannot be spread from skin to skin contact. 

If you suspect your dog has a histiocytoma, it's best to speak with a veterinarian, who can quickly provide you with a diagnosis and a treatment plan for your dog. 

Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.