Sarcoma in Dogs:
This type of cancer begins in either the bone or in the body’s soft tissues. The word sarcoma is derived from a Greek word and means “fleshy growth”. Sarcomas are a broad category of tumors classified together because of their similarities in their behaviour and outcome.
Sometimes further classification is made between bone sarcoma and soft tissue sarcoma.
Generally, sarcomas are malignant tumors that affect the “connective tissues” in the body. The connectives tissues may refer to nerves, blood vessels, bones, muscles, fat, cartilage, fibrous tissue or deep skin tissue.
Sarcoma accounts for about 15% of canine cancers. It is most common in middle-aged and older dogs, especially large or giant breeds.
The cause of sarcoma is not understood, and therefore, there is no natural way to protect against them. As with all cancers in dogs, early detection is critical.
Initially, there may be no symptoms related to the tumor. The tumor may grow very slowly over months or even years. A wide range of symptoms may present when a dog has one of the types of sarcoma. These may include:
- Enlarged lymph nodes
- Bloated stomach
- Pale gums or bad breath
- Difficulty eating or swallowing
- Issues in the limbs: swelling, limping or signs of pain.
- Unusual growths or lumps that may be soft or firm
- Unusual behavior
- Sudden loss of weight
- Increased thirst
Sarcomas are classified by various sub-types depending on the location of the cells from which they originate.
- Osteosarcoma – primary bone tumour – usually arises in the bones of the limbs
- Hemangiosarcoma (HSA) arises from endothelial cells
- Fibrosarcoma – in fibrous connective tissue
- Hemangiopericytoma – arises from pericyte cells surrounding small blood vessels
- Leiomyosarcoma – arises from smooth muscle tissue
- Liposarcoma – arises from connective tissue
- Lymphosarcoma – arises in lymph nodes and in organs with lymphoid tissue, including the bone marrow, liver and spleen
- Lymphangiosarcoma – arises from lymphatic tissue
- Neurofibrosarcoma – or nerve sheath tumor arises from nerve cells
- Rhabdomyosarcoma – arises from skeletal muscle cells
- Schwannoma – arises from nerve sheaths
- Synovial cell sarcoma – a rare form that may arise near joints
- Myxosarcoma – originates from fibroblast cells
- Malignant fibrous histiocytoma – often seen in skeletal muscles
- Undifferentiated sarcoma – difficult to characterize
Bone Cancer (Osteosarcoma) and Hemangiosarcoma are in the top five of most common dog cancers.
Hemangiosarcoma is a relatively deadly cancer most often classified separately from other soft tissue sarcomas because of its more aggressive behavior.
Osteosarcoma usually arises in the bones of the limbs. Still, it may sometimes develop in the bones of the skull, spine or ribcage.
The most accurate diagnosis is through surgical biopsy. However, fine-needle aspiration, taking a small needle and removing a sample of cells directly from the tumor for examination can produce quicker results and is less invasive. Other tests, namely bloodwork, urinalysis, lung x-rays or ultrasound, may be recommended to search for any potential spread that could inform the staging level.
The most commonly recommended treatment for soft tissue sarcomas is surgical excision with wide margins. These tumors often have “tentacles” extending beyond the tumor, and these must also be removed. Chemotherapy is not usually advised as a primary treatment unless surgery or radiation is impossible due to tumour size or location.
The predicted outcome for dogs with soft tissue sarcomas is highly variable. As described, sarcoma covers a wide range of tumors. Therefore, the prognosis depends on the type of sarcoma, its stage, size and, as in most cancers, and the timing of detection. There may be a positive outcome for many soft tissue sarcomas if the mass can be removed with wide surgical margins.
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