Histiocytoma in Dogs: Histiocytoma in dogs refers to a common benign skin tumor that forms on the surface of the skin. It is caused by an overgrowth of histiocytes, a type of white blood cell found in connective tissue.
The exact cause of histiocytomas is unknown. However, they are believed to be an immune system response to inflammation or skin injury. Certain breeds, especially boxers, cocker spaniels, and collies tend to be prone to developing these tumors. Young dogs between 4 months to 2 years of age are most commonly affected.
The most common signs of a histiocytoma include:
- A raised, firm nodule on the skin that may ulcerate. They are often described as looking like a “button” on the skin.
- Usually a solitary nodule, but some dogs may have multiple nodules.
- Most often found on the head, ears, and limbs.
- The nodules are usually 0.5 to 3 cm in diameter.
- They are often hairless and may have a pink, fleshy appearance.
- They are usually not painful and do not bother the dog.
Causes and Risk Factors of Histiocytoma
Histiocytomas are benign skin tumors that commonly affect young dogs. Several factors may increase a dog’s risk of developing these growths:
Histiocytomas typically affect dogs between 4 months to 2 years of age. They are most commonly seen in puppies and adolescent dogs as their immune systems are still developing. The good news is that most histiocytomas will spontaneously regress as a dog’s immune system matures, usually within 3 to 6 months.
Certain breeds appear more prone to histiocytomas, including Retrievers, German Shepherds, Doberman Pinschers, and Cocker Spaniels. Their higher risk could be due to genetics, but more research is needed to confirm any links between breed and histiocytoma development.
3. Immune system
A puppy’s naïve immune system may have trouble recognizing and responding to the initial development of histiocytoma cells, allowing the tumors to form. As a dog’s immune system strengthens with age and exposure, it gets better at identifying and eliminating these abnormal cells, leading to spontaneous regression of most histiocytomas.
4. Allergies or skin inflammation
Anything that irritates a dog’s skin or causes an overactive immune response could potentially increase the risk of histiocytomas. Conditions like atopic dermatitis, flea allergy dermatitis, or other skin allergies may play a role in some cases. Reducing skin inflammation and properly treating any underlying allergies may help prevent histiocytoma recurrence.
While the specific cause of most histiocytomas remains unknown, age, breed, immune system development, and skin health may all contribute to a dog’s likelihood of developing these common and usually benign skin tumors. With time and age, most dogs will outgrow their tendency for histiocytomas.
Recognizing the Symptoms of Histiocytoma
As a dog owner, it’s important to regularly check your dog for any unusual lumps or skin changes. Histiocytomas, though typically benign, can appear quickly and grow rapidly. The sooner you detect them, the sooner you can have them diagnosed and treated.
You’ll most likely first notice histiocytomas as solitary, firm nodules that seem to pop up overnight, ranging from 0.5 to 3 centimeters in diameter. They have a characteristic “button-like” appearance, growing outward from the skin. Histiocytomas are often found on the head, neck, legs or trunk of young dogs, usually less than two years of age.
Some common signs of histiocytomas include:
- Round, raised lumps on or under the skin that seem to appear rapidly
- Lumps that are dome-shaped and grow outward from the skin
- Masses that are usually pink to red in color, though some may be bluish
- Lumps that are typically not painful or itchy for your dog
- Lesions that range from 0.5 to 3 centimeters (about 0.2 to 1.2 inches) in size
- Lumps found most often on the head, neck, legs or torso of dogs under two years old
Though histiocytomas are usually harmless, noncancerous masses, they can sometimes resemble more serious tumors. It’s best to have any new lumps or growths examined by your vet, especially those that are larger than 0.5 cm, ulcerated or bleeding, or don’t disappear within 4 to 6 weeks. Your vet can examine the lump, perform tests like fine needle aspirates or biopsies if needed, and determine the best course of treatment to remove the histiocytoma and ensure your dog’s health and comfort.
Treatment Options for Histiocytoma
If your dog has been diagnosed with histiocytoma, the good news is there are several treatment options available. The course of treatment will depend on factors like your dog’s age, health, and the size, location and number of tumors.
For small, localized tumors, surgical removal is often the preferred method. A vet will anesthetize your dog and cut out the tumor, as well as a margin of healthy tissue surrounding it. The wound is then closed with stitches or staples. Surgery has a high success rate for fully eliminating the tumor. However, it may leave a small scar and does come with risks associated with anesthesia.
2. Steroid injections
Corticosteroid injections, such as prednisone, can be very effective for shrinking histiocytomas. The steroids work by reducing inflammation and suppressing the immune system. Injections are often used for tumors on the head or other areas where surgery may be difficult. Multiple injections are usually needed to fully eliminate the growth. This method avoids scarring but may cause temporary side effects like increased thirst, hunger and restlessness.
3. Topical medications
For small, superficial tumors, topical creams or ointments containing corticosteroids may be applied directly to the skin. These creams, such as triamcinolone, work similarly to steroid injections. They are very safe but may take weeks or months of regular application to shrink the tumor completely. The tumor often returns once treatment is stopped.
4. Wait and see
If the tumor is small and not bothering your dog, the vet may recommend just monitoring it for changes. Many histiocytomas will spontaneously regress and disappear on their own within a few months. However, some may persist or get larger, in which case other treatment may be recommended.
By understanding the options, you can discuss with your vet which approach is right based on your dog’s unique condition. With proper treatment, most histiocytomas can be eliminated, allowing your dog to return to full health and enjoyment of life.