Histiocytic Sarcoma in Dogs: Symptoms, Causes, and Treatment

What Is Histiocytic Sarcoma in Dogs?

Histiocytic sarcoma in dogs is a type of cancer that occurs when abnormal cells develop in various areas of a dog’s body, such as the cartilage, bone, or fat. The dog’s immune system becomes overreactive and leads to these cancerous areas forming.  

Histiocytic sarcomas are labeled as localized, disseminated (spread throughout the body), or hemophagocytic (primarily affecting blood and immune cells).

Affected dogs can have a variety of symptoms such as fever, joint pain, and difficulty breathing, depending on what type of histiocytic sarcoma is present and how advanced it is.

Histiocytic sarcoma in dogs is an aggressive cancer, but fortunately, it’s quite rare in dogs. It can occur in dogs of all ages but is most common in middle-aged and senior dogs.

While the disease itself is not an emergency, many of the symptoms that can develop because of histiocytic sarcoma should be treated as such.

For example, a dog with severe anemia due to histiocytic sarcoma would have noticeable weakness and pale gums, both of which should be treated immediately by a veterinarian.

Similarly, dogs whose cancer has already spread to multiple organs would be having concerning symptoms and this should be treated as an emergency.

If you notice any unusual behaviors or new symptoms in your dog, it is important to schedule an appointment with a veterinarian to get the right diagnosis and figure out proper treatment.

Symptoms of Histiocytic Sarcoma in Dogs

Symptoms of histiocytic sarcoma in dogs vary widely depending on which type of histiocytic sarcoma the dog has, but they may include:

• Decreased appetite

• Lethargy

• Weakness

• Weight loss

• Fever

• Joint pain

• Limping

• Coughing

• Breathing difficulties

• Vomiting

• Diarrhea

• Bruised skin

• Bleeding from nose

• Jaundice (yellowing of the skin or eyes)

• Pale gums

• Skin lumps

Causes of Histiocytic Sarcoma in Dogs

It’s unknown what causes histiocytic sarcoma in dogs, but it’s thought that there may be a genetic component, since Bernese Mountain Dogs, Flat-Coated Retrievers, and Miniature Schnauzers all have higher rates of histiocytic sarcoma.

How Veterinarians Diagnose Histiocytic Sarcoma in Dogs

A veterinarian will start with a thorough physical exam to find obvious abnormalities, such as a skin lump or difficulty breathing.

A complete history will be taken so the veterinarian knows when symptoms began and if they are getting worse.

Diagnosis of histiocytic sarcoma in dogs can be done using the following tests:

• Fine needle aspirate (FNA): A veterinarian inserts a small needle into the affected area and gently moves it around to collect a sample of cells. The cells are put on a glass slide, stained, and viewed under a microscope to determine the type of cells.

• Biopsy: A veterinarian takes a section of tissue from the sample area and sends it to a laboratory for testing. This test provides information about cancer type, grade, and management approach. This usually requires sedation or anesthesia.

• Cadet® HM assay: A sample of tissue from the affected area can be DNA-tested to provide a correct diagnosis of histiocytic sarcoma. This test is done at a specialized laboratory and may be costly.

More testing may be done to figure out the dog’s overall health and ability to handle any cancer treatment. This may include blood work, urinalysis, and imaging (X-rays, ultrasound, CT/MRI).

Treatment of Histiocytic Sarcoma in Dogs

There are treatment options for histiocytic sarcoma in dogs, but responses to treatment vary depending on how advanced the cancer is and the dog’s overall health.

Treatment options include:

• Surgery: If the cancer is localized to one part of the body, the dog may be able to have surgery. This procedure needs anesthesia, so it may not be an option for some dogs, such as those with underlying health conditions like severe heart disease.

• Chemotherapy: Dogs with histiocytic sarcoma that has spread throughout the body need chemotherapy to kill the cancer cells and slow the progression of disease.

• Corticosteroids: Steroids such as prednisone may be used alongside chemotherapy or on their own for dogs who cannot have additional treatment or whose pet parent wishes to take a palliative approach.

The veterinarian will work with the pet parent to decide which treatment option is best for each dog.

Recovery and Management of Histiocytic Sarcoma in Dogs

Unfortunately, because of the aggressive nature of histiocytic sarcoma and poor response to treatment, most dogs die from this disease within four months of diagnosis.

Keeping a dog comfortable whether they are undergoing treatment or receiving palliative care is important following diagnosis. Reducing stress in the environment, managing any other medical conditions, and recognizing signs of worsening symptoms are all important.

Humane euthanasia may be discussed by the veterinarian if the affected dog’s quality of life has become poor or if the disease is advanced at the time of diagnosis.

While this is never an easy decision, pet parents can work alongside their veterinarian to decide the most appropriate time to end your dog’s life.

Prevention of Histiocytic Sarcoma in Dogs

Because the cause is unknown, it’s difficult to know the best way to prevent histiocytic sarcoma.

However, predisposed dog breeds can be watched more closely for concerning symptoms so that if this cancer develops, it can be caught and treated early.