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Updated May 23, 2024 – For many dog owners facing a diagnosis of histiocytic sarcoma in their pet, it can be a frightening and confusing time. The cancer is rare in dogs, and information is scarce. Owners need to know the latest information to make the best decisions for their dogs and their families.  

What is Histiocytic Sarcoma?  
Histiocytic sarcoma is an aggressive cancer in dogs. Histiocytes are a type of white blood cell that reside within the tissues of almost every organ in the body and are an essential part of the immune system. They help get rid of invading pathogens and stimulate other cells of the immune system.  

Histiocytic sarcomas develop when these specialized white blood cells begin dividing uncontrollably. White blood cells in many tissues allow HS to arise almost anywhere and spread quickly.  

Risk Factors and Dog Demographics  
In the late 1970s, researchers first described histiocytic sarcoma in Bernese mountain dogs, but it has now appeared in many other breeds, including: 

  • Flat-coated retrievers  
  • Miniature schnauzers  
  • Rottweilers  
  • Labrador retrievers  
  • Pembroke Welsh corgis  
  • Golden retrievers  

Histiocytic sarcoma is more common in middle-aged and older dogs, although there are reports of the disease in dogs as young as 3. Males and females are affected equally.  

Given the strong breed predisposition for this cancer, it seems reasonable to suspect genetics play a role in disease risk. Many researchers are studying the genetics behind the disease and homing in on potential genetic markers, which could, in turn, provide the basis for genetic testing and possibly even treatment.   

In addition to genetics, the only other risk factors identified to date are a history of orthopedic disease and joint inflammation and the subsequent development of localized HS in the previously affected joint.  

Signs, Diagnosis and Treatment  
Unfortunately, the most common signs or symptoms of HS are like many other diseases and include:  

  • Lethargy  
  • Poor appetite  
  • Swelling and lameness (in cases of bone or joint involvement)  
  • Coughing  
  • Breathing difficulty  
  • Vomiting  
  • Diarrhea  

Veterinarians usually diagnose based on signs, bloodwork results, biopsy, or a fine needle aspirate of abnormal tissue. Additional tests, such as ultrasound or X-ray, are often used as adjunctive diagnostic tests to assess the extent of disease.  

Histiocytic sarcoma can take many forms, and symptoms and prognosis vary greatly depending on the subtype. The three recognized subtypes are:  

  • Localized disease, confined to one organ, usually undergoes treatment with surgery followed by chemotherapy. In many cases, patients can live more than one year (and occasionally longer), depending on the success of the surgery.    
  • Disseminated disease affects many different organs. Although chemotherapy can be used to slow the progression of the disease, the prognosis remains poor, with most patients only living a few months after diagnosis. 
  • The most aggressive subtype is hemophagocytic, characterized by cancerous histiocytes destroying blood cells. No effective treatments exist, and dogs with this form of HS only live one to two months (on average) after diagnosis.  

Sadly, most dogs are euthanized shortly after diagnosis because of the awful prognosis.   

Morris Animal Foundation Takes a Stand  
In the last 13 years, the Foundation has invested nearly $350,000 in studies focused on histiocytic sarcoma.  

Study topics we are focusing on include:   

  • Searching for new therapeutic targets  
  • Testing a new drug, trametinib, in dogs diagnosed with HS   

And we must remember the Golden Retriever Lifetime Study! Histiocytic sarcoma is one of the top five cancers diagnosed within our study dogs, a shocking statistic.  

Our team is spreading the word about the data we’ve collected on HS to the research community. We hope more researchers will use this unique dataset to examine this terrible cancer more deeply.  

Science to Save Animals Starts with YOU  
Sadly, an estimated six million dogs are diagnosed with cancer each year, and cancer is a leading cause of death in dogs. Veterinarians have limited treatment options due to a lack of funding for research focused on the many cancers that take our dogs’ lives too early.  

DONATE TODAY to support science that saves animals.

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