This Rare yet Aggressive Malignancy Mostly Strikes Big Dogs

Analysis by Dr. Karen Shaw Becker

histiocytic sarcoma in dogs

Story at-a-glance -

  • Canine histiocytic sarcoma (HS) is a rare but aggressive cancer to which certain dog breeds are predisposed
  • HS is the result of excessive and abnormal proliferation of specialized immune cells found in the tissues of almost every organ in the body; there are three subtypes of the disease
  • Symptoms of HS depend on the tissues or organs affected, and are often nonspecific and common in a wide range of other diseases
  • Response rates to treatment for HS (surgery, radiation and/or chemotherapy) are poor in a majority of affected dogs, and survival times are short

Histiocytic sarcoma (HS) is, thankfully, an uncommon cancer in dogs. However, it's an aggressive disease when it occurs, and as is the case with several other types of canine cancers, Golden Retrievers are at higher risk than other breeds. The Golden Retriever Lifetime Study is in its eighth year, and so far nine dogs enrolled in the study have developed histiocytic sarcoma.1 

Other breeds predisposed to this type of cancer are the Bernese Mountain Dog (the breed in which the disease was first discovered in the late 1970s), Rottweilers, Flat-coated Retrievers, Labrador Retrievers, Miniature Schnauzers, and Pembroke Welsh Corgis.

Histiocytic sarcoma is seen more often in middle-aged or older dogs, though there are reported cases in dogs as young as three years old. Males and females are affected equally.

How Histiocytic Sarcoma Develops

Histiocytes are a type of white blood cell found in the tissues of almost every organ in the body. They play an important role in the function of the immune system by helping the body rid itself of invading pathogens.

Occasionally, these specialized white blood cells begin dividing uncontrollably; histiocytic sarcoma is the result of the excessive and abnormal proliferation of these immune cells. Because this type of cell is found in so many different tissues of the body, the sarcomas can develop almost anywhere and spread quickly.

There are three forms or subtypes of histiocytic sarcoma: localized, disseminated and hemophagocytic.

  • The localized form is confined to one organ. Conventional treatment typically involves surgery followed by chemotherapy. In many cases, dogs with this subtype can live more than a year and occasionally longer.
  • As the name suggests, disseminated HS affects many different organs. Chemotherapy is sometimes used to slow disease progression, but most dogs with this form live only a few months.
  • Hemophagocytic HS is the most aggressive subtype. There are no effective treatments and survival times are only one to two months.

The underlying cause for histiocytic sarcoma has yet to be determined; however, it may be in part inherited based on the breed predispositions mentioned above. Other factors may include genetic and molecular mutations, and immune system dysregulation.

The only other risk factor identified to date is a history of orthopedic disease and inflammation when HS is localized to a joint.

Symptoms to Watch For

Symptoms of HS depend on the tissues or organs affected, and are often nonspecific and common in a wide range of disorders, e.g., lack of appetite, weight loss, lethargy, or depression.

In dogs in which the cancer affects the limbs or joints, there's often an obvious mass, as well as lameness. If the lungs are involved, symptoms can include coughing, difficulty breathing, exercise intolerance and lethargy.

Diagnosis, Conventional Treatment Options and Prognosis

Histiocytic sarcoma can be difficult to diagnose. A fine needle aspirate of the mass and cytologic analysis is typically performed, however, often a tissue biopsy is also required along with, in some cases, special stains.

The most common sites for metastatic (disease spread) as well as the disseminated form of the disease are the lungs, lymph nodes, bone marrow, spleen, liver and brain. Often veterinary oncologists will also recommend chest x-rays, abdominal ultrasound, blood work, urinalysis, and, in certain cases, advanced imaging with MRI or CT-scan.

Complete staging is also required to determine how far the cancer has spread and where — especially if conventional treatments are planned — so the integrative veterinary oncologist can design an appropriate protocol and monitor the effectiveness of treatments. Integrative oncologists also use nutraceuticals and supplements to reduce drug side effects and modulate the immune system before, during and after cancer therapy.

Adjunctive integrative protocols that can often be used concurrently with standard of care include ozone therapy, hyperbaric oxygen therapy, IV vitamin C, mistletoe and curcumin therapy, as well as dietary interventions.

Sadly, the only conventional medicine treatments available for this terrible cancer are the usual menu of surgery, radiation therapy, and/or chemotherapy, and the prognosis is considered "guarded to grave" for most dogs. According to North Carolina State University Veterinary Hospital:

"Untreated, the clinical course of disseminated histiocytic sarcoma is rapid and fatal. Localized histiocytic sarcoma is sometimes more slowly progres­sive but can be extremely painful and cause a poor quality of life. Overall, response rates to treatment are poor and survival times are short (3-4 months).

A subset of dogs with localized histiocytic sarcoma treated with aggressive surgery and chemotherapy can enjoy long term survival, on average between 1.5 to ~ 3 years.

The prognosis for hemophagocytic histiocytic sarcoma is considered grave (< 2 months)."2

As you can see, histiocytic sarcoma is a disease no dog parent wants their pet to be diagnosed with. Hopefully, the Golden Retriever Lifetime Study, sponsored by the Morris Animal Foundation, might one day provide important clues to understanding more about this disease.

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5 Ways to Reduce Your Dog's Cancer Risk

1. Don't allow your dog to become overweight — Studies show that restricting the number of calories an animal eats prevents and/or delays the progression of tumor development across species. Fewer calories cause the cells of the body to block tumor growth, whereas too many calories can lead to obesity, and obesity is closely linked to increased cancer risk in humans.

There is a connection between too much glucose, increased insulin sensitivity, inflammation, and oxidative stress — all factors in obesity — and cancer. It's important to remember that fat doesn't just sit on your pet's body harmlessly. It produces inflammation that can promote tumor development.

2. Feed an anti-inflammatory diet — Anything that creates or promotes inflammation in the body increases the risk for cancer. Current research suggests cancer is actually a chronic inflammatory disease, fueled by sugar (carbohydrates). The inflammatory process creates an environment in which abnormal cells proliferate.

Cancer cells require the glucose in carbohydrates to grow and multiply, so you want to eliminate that cancer energy source. Carbs to remove from your pet's diet include processed grains and legumes, fruits with fructose, and starchy vegetables like potatoes.

Keep in mind that all dry pet food contains some form of starch. It may be grain-free, but it can't be starch-free because it's not possible to manufacture kibble without using some type of starch.

Cancer cells generally can't use dietary fats for energy, so high amounts of good quality fats are nutritionally beneficial for dogs fighting cancer, along with a reduced amount of protein and no carbs.

Another major contributor to inflammatory conditions is a diet too high in omega-6 fatty acids and too low in omega-3s. Omega-6s increase inflammation while the omega-3s do the reverse. Processed pet food is typically loaded with omega-6 fatty acids and deficient in omega-3s.

A healthy diet for your pet — one that is anti-inflammatory and anticancer — consists of real, whole foods, preferably raw. It should include high-quality protein, including muscle meat, organs and bone.

It should also include high amounts of animal fat, high levels of EPA and DHA (omega-3 fatty acids), and a few fresh cut, low glycemic veggies. This species-appropriate diet is high in moisture content and contains no grains or starches.

I also recommend making sure the diet is balanced following the ancestral diet recommendations, which have much more rigorous standards (higher amounts of minerals and vitamins) than our current dietary recommendations for pets (AAFCO).

A few beneficial supplements like probiotics, medicinal mushrooms, digestive enzymes, and polyphenol-rich super green foods or herbs can also be very beneficial to enhance immune function.

3. Reduce or eliminate your pet's exposure to toxins — These include chemical pesticides like flea and tick preventives, lawn chemicals (weed killers, herbicides, etc.), tobacco smoke, flame-retardants (most commonly found on nonorganic pet beds), and household cleaners (detergents, soaps, cleansers, dryer sheets, room deodorizers).

Because we live in a toxic world and avoiding all chemical exposure is nearly impossible, I also suggest offering a periodic detoxification protocol to your pet.

4. Especially if your dog is a large or giant breed, hold off neutering or spaying until the age of 18 months to 2 years — Studies have linked spaying and neutering to increasing cancer rates in dogs. Even better, investigate alternative ways to sterilize your pet without upsetting his or her important hormone balance.

5. Refuse unnecessary vaccinations — Vaccine protocols should be tailored to minimize risk and maximize protection, taking into account the breed, background, nutritional status, lifestyle, and overall vitality of the pet.