Histiocytic sarcoma in dogs is not a very common cancer and therefore there is not much literature about this type of malignancy. This form of cancer has been identified as being more common in certain breeds than others. The most commonly affected breeds include Bernese mountain dogs, Rottweilers, flat coated Retrievers, Doberman pinschers, Golden retrievers and Labrador retrievers, however any breed can be occasionally affected. Most diagnosed dogs are middle aged dogs. Prognosis for this type of cancer is not very good as cancer spread happens in 70 to 91 percent of dogs, but new research shows potential increase in survival times with chemo for good candidates.
Histiocytic is a term that derives from histiocytes, a special type of cell found in animals which plays a role in the dog's immune system.
Histiocytes are immune cells that originate from the dog's bone marrow. Once released from the bone marrow, these cells travel into the dog's bloodstream initially as monocytes which mature into histiocytes only once they have entered different tissues. There are three main subtypes of histiocytes: dendritic cells, macrophages, and Langerhans cells.
The term sarcoma, on the other hand, derives from the Greek word sarx, meaning "flesh." Sarcomas are given various different names based on what type of tissue they originate from and resemble.
For instance, osteosarcomas are sarcomas that resemble bone, liposarcomas are sarcomas that resemble fat, chondrosarcomas resemble cartilage, leiomyosarcomas resemble smooth muscles. Histiocytic sarcomas are sarcomas instead that originate from histiocytes.
Symptoms of Histiocytic Sarcoma in Dogs
The symptoms of histiocytic sarcoma in dogs are quite vague, and since this condition is relatively uncommon, a delayed diagnosis is not unusual. Symptoms may vary from one dog and another and are typically initially related to the area from which the tumor originates.
For instance, in the case of histiocytic sarcoma affecting the dog's lungs, the affected dog will be typically exhibiting respiratory signs such as coughing and trouble breathing. If it involves the nervous system, affected dogs may develop seizures, incoordination and paralysis. When a leg is affected, the dog develops lameness and limping.
More vague, generic signs may be seen in most dogs and these comprise lethargy, loss of appetite and weight loss. Weakness may be seen as a result of anemia (low red blood cells). As the cancer advances, it eventually metastasizes to the lymph node, liver, kidney, and central nervous system
Localized and Disseminated Forms
Histiocytic sarcoma in dogs is a progressive form of cancer than tends to spread. It's therefore important to catch it at its earliest stages for a better prognosis.
When the cancer is localised to only its site of origin, it is referred to as a localized histiocytic sarcoma (LHS). Common areas of origin may include the dog's skin, spleen, lung, bone marrow, central nervous system, tissue around the joints and lymph nodes.
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When this cancer is caught when it is still localized, surgical removal with wide margins is recommended. If the cancer is localized to the tissue of a joint, this may therefore mean amputation of a leg, if it's localized to the spleen it may translate into a splenectomy.
This cancer as it progresses will affect other body parts. In a primary cancer affecting the spleen, the cancer may therefore spread secondarily to the liver ( the splenic vein drains into the liver's portal vein ) or lungs, in a primary cancer affecting the lungs, secondary spread may spread to the lymph nodes and so on.
There is also a disseminated form that affects multiple organ systems at once which is known as s disseminated histiocytic sarcoma (DHS), formerly known as malignant histiocytosis, and an hemophagocytic form which originates from splenic tissue and rapidly progresses.
Treatment of Histiocytic Sarcoma in Dogs
Treatment for this form of cancer varies based on whether the dog is suffering from the localized, disseminated or hemophagocytic form.
In order to check for spread to other organs, an extensive battery of tests may be needed. These test may include blood work, urinalysis, chest x-rays (three views), abdominal ultrasound and bone marrow and regional lymph node aspirates. This process is known as staging.
Staging allows the vet to get a better feel on the effects the cancer has on the dog's body as well as the dog's ability to handle treatment.
If the cancer is found to be localized, then surgical removal of the primary tumor followed up by adjuvant chemotherapy may be recommended. Surgery alone is not productive considering that a study found no improvement in survival times in dogs undergoing surgery when compared to no treatment at all.
However, if the cancer has spread and the dog is in an inoperable state, then that is when chemo is recommended as primary treatment. Sadly, the prognosis for dogs affected by the hemophagocytic form is poor to grave, with mean survival times of 7.1 weeks following diagnosis.
There are different types of chemo used to manage this type of cancer. In particular, lomustine (CCNU) chemotherapy has revealed some promising results in a study.
With a therapeutic response rate approaching 50 percent, 59 dogs administered lomustine every 3 to 4 weeks had a . median survival time of 106 days, while dogs who has partial or complete responses had a median survival time approaching 6 months (172 days). Non-responders on the other hand, had a median survival time of 60 days. Three dogs treated with minimal residual disease following surgery instead went on to live more than 14 months.
" Anemic dogs lived a median of 28 days compared with 163 days in dogs without anemia, and dogs with thrombocytopenia lived a median of 21 days compared with 165 days in dogs without thrombocytopenia. Hypoalbuminemic dogs lived a median of 28 days
compared with 163 days in dogs with normal serum albumin concentration. Dogs with splenic involvement lived a median of 58 days compared with 165 days in dogs with normal spleens."~J Vet Intern Med 2007;21:121–126
- Penn Vet Histiocytic Sarcoma in Dogs Clinical Oncology Service Ryan Veterinary Hospital of the University of Pennsylvania
- Veterinary Hematology - E-Book: A Diagnostic Guide and Color Atlas, By John W. Harvey
- CCNU for the Treatment of Dogs with Histiocytic Sarcoma Katherine A. Skorupski, Craig A. Clifford, Melissa C. Paoloni, Ana Lara-Garcia, Lisa Barber, Michael S. Kent, Amy K. LeBlanc, Aarti Sabhlok, Elizabeth A. Mauldin, Frances S. Shofer,C. Guillermo Couto, and Karin U. Sørenmo