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Updated May 19, 2026 — 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 are found in 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. Because histiocytes are located all over the body, histiocytic sarcoma can arise almost anywhere in the body and spread quickly.

What Dog Breeds Are at Risk for Histiocytic Sarcoma? 
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
  • 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. Researchers are studying the genetics behind the disease and working to identify potential genetic markers, which could 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 histiocytic sarcoma in the previously affected joint.

What Are the Signs, Diagnosis and Treatment Options for Histiocytic Sarcoma in Dogs? 
Unfortunately, the most common signs or symptoms of histiocytic sarcoma are similar to 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 tools 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:

  1. 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.
  2. 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.
  3. The most aggressive subtype is hemophagocytic, characterized by cancerous histiocytes destroying blood cells. No effective treatments exist, and dogs with this form of histiocytic sarcoma only live one to two months (on average) after diagnosis.

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

What Research Is Morris Animal Foundation Funding on Histiocytic Sarcoma? 
Morris Animal Foundation has invested more than $500,000 in histiocytic sarcoma research over the past 18 years and our active studies represent some of the most promising science to date.

Studying Genetic Drivers of Histiocytic Sarcoma Tumors — Researchers at Colorado State University know that about half of dogs with histiocytic sarcoma share the same genetic code error in their tumors. This study is conducting a genome-wide screening to identify what is happening in the other half — mapping genetic changes and testing cell lines for drug sensitivity to help predict how this cancer progresses and which treatments may work best for individual dogs.

Studying the Genetics of Histiocytic Sarcoma in Golden Retrievers — A team at the Rennes Institute of Genetics & Development is using whole-genome sequencing of 90 golden retrievers to identify the predisposing genetic variants that make the breed more vulnerable to histiocytic sarcoma. For Bernese mountain dogs, this type of research has already led to a genetic risk test that breeders can use to reduce the number of affected dogs. This study is the first step toward a similar tool for golden retrievers.

Evaluating a Promising Cancer Drug — Dogs diagnosed with histiocytic sarcoma have median survival times of just weeks to months — which is why researchers at Colorado State University are evaluating Parthenolide (PTL), a plant-based drug that has already shown promise against histiocytic sarcoma, mast cell tumor, and lymphoma cells in the laboratory. This study will determine which canine cancers respond best to PTL, both alone and in combination with standard chemotherapy, with findings intended to inform future clinical trials.

Investigating the Use of a Cutting-Edge Immunotherapy Platform to Treat Histiocytic Sarcoma in Dogs — Researchers at Michigan State University are evaluating an innovative immunotherapy approach using engineered intracellular bacteria called quasiorganelles to deliver proteins directly into histiocytic sarcoma cells and the surrounding immune cells. The goal is to stop uncontrolled cancer growth and direct the immune system to eliminate cancer cells. If the initial pilot study shows safety and effectiveness, the team plans to expand to a multi-center clinical trial for dogs with advanced disease.

And we can’t forget the Golden Retriever Lifetime Study! Histiocytic sarcoma is one of the top five cancers diagnosed within our Study dogs — as of May 2026, 66 Study dogs have been diagnosed — a striking finding for a cancer considered rare in the general dog population. Our team is actively sharing all GRLS data with the research community, with the hope that more researchers will use this unique dataset to examine this cancer more deeply.

Science to Save Animals Starts With YOU 
Sadly, an estimated 6 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 fund lifesaving science for dogs and animals everywhere. 

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