Soft Tissue Sarcomas in Dogs
Sarcomas are malignant tumors that arise from various sources, including connective tissue, fat, blood vessels, nerve sheaths, and muscle cells. Collectively they account for about 15 percent of all cancers in dogs. There is a genetic disposition among German Shepherd Dogs, Boxers, Saint Bernards, Basset Hounds, Great Danes, and Golden Retrievers.
Sarcomas occur on the surface of the body and within organs. They tend to grow slowly and metastasize only when they have been present for some time. Metastases usually involve the lungs and liver. Some sarcomas are well defined and appear to be encapsulated; others infiltrate the surrounding tissue and have no distinct margins. Sarcomas within body cavities often grow to a large size before being discovered.
Soft tissue sarcoma is diagnosed using X-rays, ultrasonography, CT scan, and tissue biopsy.
The most common sarcomas found in dogs are:
- Hemangiopericytoma, arising from cells surrounding small arteries
- Fibrosarcoma, arising from fibrous connective tissue
- Hemangiosarcoma, arising from cells that make up the lining of small blood vessels
- Schwannoma, a tumor of nerve sheaths
- Osteosarcoma, a tumor of bones
- Lymphoma, arising in lymph nodes and in organs that contain lymphoid tissue, such as the spleen, liver, and bone marrow
Treatment: The World Health Organization has established a staging system for canine soft tissue sarcomas similar to that described for mast cell tumors. Depending on the type of sarcoma and the extent of local involvement, treatment may involve surgical excision with a margin of normal tissue, radiation therapy, hyperthermia, and chemotherapy. A specific treatment plan often uses a combination of therapies. The prognosis depends on the stage of the tumor at the time of treatment.
Lymphoma, also called lymphosarcoma, is a type of cancer that arises (often simultaneously) in lymph nodes and in organs that contain lymphoid tissue such as the spleen, liver, and bone marrow. The disease affects middle-aged and older dogs. It should be suspected when enlarged lymph nodes are found in the groin, armpit, neck, or chest. Affected dogs appear lethargic, eat poorly, and lose weight. The liver and spleen are often enlarged.
Chest involvement results in pleural effusion and severe shortness of breath. Skin involvement produces itchy patches or nodules on the surface of the skin that mimic other skin diseases. Intestinal involvement causes vomiting and diarrhea.
A complete blood count may show anemia and immature white blood cells. The serum calcium is elevated in 20 percent of dogs with lymphoma. Blood and liver function tests are usually abnormal. A bone marrow biopsy is helpful in determining if the disease is widespread.
Chest and abdominal X-rays and ultrasonography are particularly valuable in identifying enlarged lymph nodes, organs, and masses. A diagnosis can also be made by fine needle aspiration of an enlarged lymph node. In questionable cases, the entire lymph node should be removed for more complete evaluation.
A company in Great Britain called Pet Screening offers a genetic screening test for canine lymphoma, based on genetic markers in a blood sample. They suggest periodic screenings to detect lymphomas early on.
Treatment: Lymphoma localized to a single lymph node may be cured by surgical removal of the involved node. However, in most dogs the disease is widespread and a cure is unlikely. Chemotherapy using several agents offers the best chance of remission, which may last a year or longer. When a dog comes out of remission, chemotherapy “rescue protocols” may be used to induce a second or even a third remission.
Hemangiosarcoma is a tumor of the vascular tissues. This cancer may be noticed as a lump on a rib or an abdominal swelling, but can progress unnoticed while growing on the heart, liver, or spleen. The cancerous growths are quite fragile and often break off, “seeding” cancer throughout the body. Alternatively, the first sign may be sudden death as a large area of tumor ruptures and the dog bleeds to death internally.
Treatment: Surgery and chemotherapy may help prolong survival times but cures are virtually never seen, even with surgery done before there are detectable metastases.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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