Defining Soft Tissue Sarcomas
Sarcomas are malignant tumors that arise from a variety of different tissues, including bone, cartilage, muscle, nerves, blood vessels, connective tissue and lymph tissue. They are classified together as “soft tissue sarcomas” because of their similar biological behavior and treatment protocols. Sarcomas are fairly common in domestic dogs and account for roughly 15 percent of all canine cancers. The most common soft tissue sarcomas in dogs are:
- Fibrosarcoma – arises from fibrous connective tissue
- Fibrous histiocytoma
- Hemangiopericytoma – arises from cells surrounding small blood vessels
- Hemangiosarcoma – arises from cells that line small blood vessels; often classified separately from the other categories of soft tissue sarcomas due to its aggressive biological behavior
- Leiomyosarcoma – arises from smooth muscle tissue
- Liposarcoma – arises from connective tissue
- Lymphoma (Lymphosarcoma) – arises in lymph nodes and in organs with lymphoid tissue, including the bone marrow, liver and spleen
- Lymphangiosarcoma – arises from lymphatic tissue
- Neurofibrosarcoma – arises from nerve cells
- Osteosarcoma – arises from bone
- Rhabdomyosarcoma – arises from muscle cells
- Schwannoma – arises from nerve sheaths
- Synovial cell sarcoma
Some soft tissue sarcomas have been associated with metal implants, exposure to radiation, implanted microchips and certain parasitic infestations. Sarcomas at the site of injections (shots) are uncommon in dogs but do occur more commonly in cats. Most sarcomas arise spontaneously. Genetics and environmental conditions may play a role in the development of soft tissue sarcomas in dogs, but research in this area is still in its infancy. Because we don’t understand what causes them, there is no real way to prevent soft tissue sarcomas. Early detection and treatment are the best ways to address these tumors.
Soft Tissue Sarcomas – Symptoms and Signs
Soft tissue sarcomas typically develop either on the body surface or inside organs (kidneys, liver, lungs, spleen, heart, others). They usually grow slowly and then metastasize (spread) after they have become well-established in one location. Sarcomas inside body organs often are quite large before they are discovered. The liver and lungs are the most common sites of metastasis. Some soft tissue sarcomas are well-defined and appear to be enveloped or encapsulated, while others are invasive and infiltrate surrounding tissues, having no distinct borders. They are most common in middle-aged and older dogs, especially in large and giant breeds. In most cases, these tumors are diagnosed when a dog’s owner brings it to the veterinarian because of a noticeable and progressively enlarging superficial mass. The location of the sarcoma will guide its signs. For example, dogs with soft tissue sarcomas in their mouth may have bad breath (halitosis), difficulty eating or swallowing and/or nose bleeds (epistaxis). Dogs with these tumors in their gastrointestinal tract often present with vomiting and diarrhea.
Soft Tissue Sarcomas – Diagnosis and Test
Soft tissue sarcomas can only be definitively diagnosed by microscopic examination of tissue samples taken from the tumors by tissue biopsy. This is called histopathology. Radiographic imaging (X-rays) can often be helpful to define the nature and extent of the tumor. Chest X-rays can also be helpful to identify any metastasis to the lungs or thoracic cavity. Cell samples taken by a procedure known as fine needle aspiration can be evaluated to identify the type of soft tissue cells that are creating the mass. More advanced diagnostic procedures, including computed tomography (CT scan) and magnetic resonance imaging (MRI), can be used to delineate the exact nature and extent of the tumor and assist the veterinarian in planning the best surgical approach to remove it.
Soft Tissue Sarcomas – Treatment and Prognosis
The goal of treating soft tissue sarcomas is to completely eradicate all cancerous tissue – in other words, to get rid of the tumor. If the tumor cannot be eliminated entirely, the goal becomes preventing or at least delaying the spread of cancerous cells to other tissues. Aggressive surgical removal of soft tissue sarcomas is reported to be the best way to treat this condition. The surgeon will try to get very wide margins around the tumor, because soft tissue sarcomas tend to invade nearby tissues. Palliative therapy, including radiation and general supportive care, can be used to help alleviate the pain and discomfort that usually accompany this condition. In some cases, radiation may be recommended before surgical resection, especially if the tumor is located in an area that isn’t easily surgically accessible for removal. Chemotherapy, which is treatment with injectable or oral anti-cancer medications, is available for dogs with high-grade tumors or those with metastatic disease. A number of different drugs, including doxorubicin, mitoxantrone, platinum drugs and ifosfamide, and combinations of these medications, have been used with some degree of success to treat soft tissue sarcomas in dogs.
The outlook for dogs with soft tissue sarcomas is highly variable. Tumors located in the belly cavity tend to be metastatic – which means that they tend to spread to other locations. Sarcomas in the mouth (oral cavity) are difficult to treat surgically or with radiation because of their location. Dogs with soft tissue sarcomas that have metastasized at the time of diagnosis usually have a poor prognosis. However, many dogs with soft tissue sarcomas can be successfully treated if the mass can be removed with wide surgical margins.