Soft Tissue Sarcomas
Soft tissue sarcoma is a general term that refers to a group of tumors that form in tissues of mesenchymal origin such as the connective tissue (e.g. fat, smooth-muscle, blood vessels, lymph vessels, skeletal muscle, etc.) They tend to have similar histologic appearance and biological behavior, and can be either benign (noncancerous) or malignant (cancerous). Soft tissue sarcomas can arise in any part of the body although skin and subcutaneous (the layer of tissue directly underlying the skin) tumors are the most commonly observed.
Soft tissue sarcomas (STS) behave in a locally invasive manner. The incidence of metastasis (spread to different sites) varies from about 8% to 20%. This rate is generally lower than other types of tumors in animals; therefore, aggressive local control of the disease is the key goal.
DIAGNOSIS
The individual STS tumor types can be challenging to distinguish between. Fine-needle aspirates or tissue biopsies are required to confirm a diagnosis. Not infrequently, additional pathology tests are required to more precisely determine the tissue of origin. Also, additional tests are performed in order to evaluate how advanced the disease is. The tests will depend on the type of soft tissue sarcoma but generally involve blood and serum biochemical tests, chest X-rays, and imaging.
DISEASE STAGING
Imaging studies of the local tumor may be recommended prior to planning the surgical removal of the tumor and/or radiation therapy, especially in animals with suspected intra-abdominal soft-tissue sarcomas. Advanced imaging techniques such as CT (computed tomography) and MRI (magnetic resonance imaging) are especially useful due to their high level of resolution and detail.
Diagnostic tests that evaluate whether the tumors have spread to other organs include chest X-rays (to check for metastasis to the lungs), abdominal ultrasound (to check for metastasis in the spleen, liver, etc.), and fine-needle aspirates/biopsy of regional lymph nodes (to check for lymph node metastasis). At the very minimum, chest X-rays should be performed prior to initiating treatment since soft tissue sarcomas commonly spread to the lungs. Lymph node metastasis is not common for typical soft tissue sarcoma but their biopsy/cytology should be assessed in animals whose lymph nodes appear abnormal and/or whose specific tumor type is suspected to have a high metastatic potential.
TREATMENT OPTIONS
Surgery
Invasive STS can be challenging to treat as they expand into surrounding structures and require extensive surgery to achieve complete removal. The first surgery is the key opportunity to achieve complete excision. A general principle for removing such tumors is that the tumor should be removed with a significant margin of normal tissue around it (in all directions) to ensure the complete removal of all malignant cells. An experienced, board-certified veterinary surgeon is recommended for STS resections.
Some STS appear in locations in which complete resection is difficult without disturbing normal tissue. Depending upon the tumor location, such surgeries as limb amputation, rib resection, and nasal/jaw reconstructions may be required. It is important to note that veterinary patients recover quickly and cosmetically even from these more extensive surgeries.
Radiation Therapy
Radiation therapy can be combined with surgery in either a pre or post-surgical manner. If given prior to surgery, the tumor may decrease in size and be subsequently easier to remove. If radiation therapy is given after surgery, it is intended to eradicate tumor cells that may have been left behind during an incomplete excision.
Veterinary patients are quite tolerant of this form of cancer treatment and it can increase the chances for successful long-term disease management. This is a highly specialized form of cancer treatment and is provided by veterinary radiation oncologists at:
- New England Veterinary Oncology Group (NEVOG), Waltham, MA. 781-684-8688
- Angell Memorial Animal Hospital, Boston, MA. 781-522-7282
- Tufts University School of Veterinary Medicine, N. Grafton, MA. 508-839-5395
Chemotherapy
The benefit of chemotherapy in the treatment of soft tissue sarcomas has not been quantified. However, recent research has shown that chemotherapy can delay the regrowth or spread of aggressive soft tissue sarcomas. Chemotherapeutic agents used include doxorubicin, carboplatin, and certain alkylating agents. Low-dose daily metronomic chemotherapy is also showing promise as treatment for STS. In general, chemotherapy is recommended in patients deemed to have an aggressive tumor (high grade), metastatic disease, and/or intra-abdominal tumors.
PROGNOSIS
The prognosis for soft tissue sarcoma is variable, though long-term control or cure is possible. Local control of the tumor is very challenging and local tumor recurrence rates after surgery (with or without radiation) range from 7% to 32%. Poor prognostic factors for local tumor recurrence include large tumor size, incomplete surgical removal, and high histologic tumor grade (high grade corresponds with aggressive tumor behavior). Management of recurrent soft tissue sarcomas is usually more difficult than the original tumor, emphasizing the need for aggressive treatment of the initial tumor. Because the median time for tumor recurrence is 368 days, the pets should undergo long-term follow-up and frequent check-ups. The metastatic rate for soft tissue sarcomas varies from 8% to 17% with a median time to metastasis of 1 year, depending on the tumor’s properties. The median survival time for dogs with soft tissue sarcomas is 1416 days with surgical treatment and 2270 days with surgical and radiation treatment. Overall, up to 33% of dogs eventually die of tumor-related causes.
Types of Soft Tissue Sarcomas |
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| Tissue of origin | Benign tumor | Malignant tumor | Primary sties | Risk of malignant tumor metastasis | Organ of metastasis |
| Adipose (fat) tissue | Lipoma | Liposarcoma | Limbs, abdominal or chest cavity | Low to moderate | Lungs, liver, spleen, bone |
| Fibrous tissue | Fibroma | Fibrosarcoma | Limbs, oral cavity | Low to moderate | Lungs |
| Histiocytic cells | Histiocytoma | Histiocytic sarcoma | Limbs | Moderate to high | Lymph nodes, lungs, spleen, liver, kidneys |
| Lymph vessels | Lymphangioma | Lymphangiosarcoma | Limbs | Moderate | Lymph nodes |
| Blood vessels | Hemangioma | Hemangiosarcoma | Spleen, heart, liver, muscle, bone, kidneys | High | Lungs, liver, lymph nodes, distant dermal sites |
| Nervous tissue | – | Peripheral nerve sheath tumor | Limbs | Low to moderate | Lugns |
| Skeletal muscle | Rhabdomyoma | Rhabdomyosarcoma | Tongue, larynx, heart, bladder | Low to moderate | Lungs, liver, spleen, kidneys |
| Synovial tissue | Synovioma | Synovial cell sarcoma | Joints | Moderate to high | Lymph nodes, lungs |
| Myxoma tissue | Myxoma | Myxosarcoma | Limbs, joints | Low to moderate | Lungs |
| Source: Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology, St. Louis: Saunders Elsevier, 2007. | |||||