Hstiocytic sarcoma (HS) is a malignant disease found most often in Bernese Mountain dogs, retrievers and rottweilers. Males are more commonly affected than females and it can occur at any age. It is also called Histiocytic sarcoma complex, malignant histiocytosis and disseminated histocytic sarcoma. There are two forms of the disease, localized or disseminated. The localized disease occurs when a lump or lumps are found in one specific area, usually on the legs and these have not spread to the lymph nodes. Localized HS tends to invade skin, subcutaneous tissue and joints. The disseminated disease occurs when tumor cells spread beyond the local lymph nodes to the lung, liver, spleen, gastrointestinal system, eyes, central nervous system, skin, muscles, bone and/or the bone marrow. The tumor is thought is arise from interstitial dendritic cells that become malignant.
The signs of HS vary widely due to the many different organs that can be involved. In the early stages of localized disease, most dogs have no clinical signs of disease. Usually, they come in for an examination after a lump is found. As the disease progresses, lethargy, anorexia, lameness and coughing are the most common clinic signs. Unless a mass is found and biopsied, diagnosis can be difficult due to the nonspecific clinical signs. Anemia is the most common abnormality on general lab work. Dogs may also have decreased numbers of white blood cells, increases in liver enzymes and an increased number of histiocytes in the blood and bone marrow. X-rays may show masses in the lung or mediastinum. These masses leak fluid causing pleural effusion affecting the dog’s breathing. X-rays may also show destruction of bone or joints.
Surgical removal of solitary nodules is the treatment of choice at this time. Dogs without evidence of cancer spread who underwent amputation of the affected limb lived 6 months. Dog who had chemotherapy with amputation lived an average of 19 months. Dogs with disseminated disease fare far worse. In one study, half of the dogs with HS responded to chemotherapy and lived an average of 6 months. Dogs who responded poorly to chemotherapy only survived for about 2 months.
To clarify, HS is not the same as cutaneous histiocytoma. Histiocytomas are benign tumors of young dogs. These pink raspberry looking masses occur in thinly haired areas on the legs, head and neck. They grow quickly and can resolve on their own. I see them most often in Boxers and Dachshunds although Cocker Spaniels, Great Danes, Shetland Sheepdogs and Bull Terriers are also reported in the literature.
-Shell, Linda. ‘Malignant Histocytosis/Histiocytic Sarcoma’ Associate Database, VIN, last updated 12/11/2003.
-Skorupski, Katherine. ‘The Histiocytic Diseases: A Clinical Perspective’ Canine Medicine Symposium 2009, UCDCM2009, VIN