Localized histiocytic sarcoma,  disseminated histiocytic sarcoma and malignant histiocytosis are fairly rare tumors overall but occur with high incidence in Bernese Mountain dogs, Rottweilers, Flat Coated Retrievers, and Golden Retrievers. Histiocytic sarcomas are very aggressive tumors, and can therefore become very invasive (destroy normal surrounding tissues) as well as have a high rate of metastasis (spreading to other areas of the body). Localized histiocytic sarcoma lesions most commonly are found in the spleen, lymph nodes, lung, bone marrow, skin, brain, and joints of the limbs. Disseminated histiocytic sarcoma and malignant histiocytosis are multi-system, rapidly progressive diseases in which there is simultaneous involvement of multiple organs such as the spleen, lymph nodes, lung, bone marrow, and skin.
 

What causes this cancer in dogs?

• The cause of this group of diseases is largely unknown.

What are the most common clinical signs of this disease?

•  Dogs with histiocytic sarcoma typically have non-specific signs such as anorexia, weight loss, and decreased energy.

• Other signs depend on the organs involved and are usually a consequence of destructive mass formation. For example, if there is a large mass in the lungs, a dog may experience coughing or difficulty breathing. If the brain is involved, you may see seizures, incoordination, and paralysis. If a joint is involved, lameness or limping is often seen.

How is histiocytic sarcoma diagnosed?

• Most histiocytic sarcomas can be diagnosed via cytology (needle aspiration; where a small needle is inserted into the mass and cells are removed and evaluated under a microscope) or biopsy (a piece of tumor tissue is removed under sedation). Occasionally, a histiocytic sarcoma tumor can look identical to other types of tumors, so additional tests may be recommended to get a definitive diagnosis.
• Due to the high risk of dissemination (spreading throughout the body) we typically recommend blood work, radiographs of the chest, and an ultrasound of the abdomen to look for evidence of disease spread. An evaluation of your pets’ bone marrow may also be recommended, especially if your pet is anemic. A bone marrow evaluation does require mild sedation, but is typically not painful for your pet. 

How is this cancer treated?

• If your pet has a localized histiocytic sarcoma, surgery or radiation therapy may be recommended as part of the treatment protocol. If the lesion is periarticular (in the joint tissue of a limb), amputation of that limb may be recommended or radiation therapy to the joint may be recommended.
• If your pet has disseminated histiocytic sarcoma, surgery will likely not be recommended.
• Due to the high rate of metastasis (spreading), some form of chemotherapy is usually recommended. There are several chemotherapy medications that have shown effectiveness in patients with histiocytic sarcoma, such as lomustine and doxorubicin.
  
  • Will chemotherapy be recommended?

If there is spread of the disease at diagnosis or there is a high chance of the disease spreading then chemotherapy will be recommended.

• Will radiation therapy be recommended?

If the disease is mostly localized, then radiation therapy will be recommended.

What is the prognosis for my dog with histiocytic sarcoma?

• Longer survival times have been seen in dogs that have microscopic disease or have localized tumors that have been surgically removed. Disseminated histiocytic sarcomas and malignant histiocytosis are both aggressive diseases that have a generally poor response to therapy. There are individual animals that can, however, do well.

What is on the horizon for this cancer?

• New drugs are currently being investigated for their effectiveness in the treatment of this disease. There is some indication that some drugs used to treat women with osteoporosis may be of benefit.