Soft Tissue Sarcomas in Dogs
What are Soft Tissue Sarcomas?
Soft tissue sarcomas are tumors originating from structural and connective tissues. They are most often evident as masses in the skin or subcutaneous tissues. Although seemingly diverse in their tissues of origin, these tumors share similar biologic behavior and are therefore considered together. Examples of soft tissue sarcomas include fibrosarcoma, hemangiopericytoma, liposarcoma, nerve sheath tumor and leiomyosarcoma.
Soft tissue sarcomas are locally invasive tumors and readily invade adjacent normal issues with finger-like projections. The rate of metastasis can be predicted by determining the histologic grade of an individual tumor. Low-grade tumors have a low rate of metastasis (10%), while high-grade tumors have a moderate rate of metastasis (40%).
Diagnostic tests are recommended to determine which sites in the body are involved. These tests include:
- Complete blood count (CBC)
- Serum biochemistry panel
- Urinalysis (U/A)
- Regional lymph node evaluation
- Thoracic radiographs
- +/- Abdominal sonogram (indicated for tumors on the caudal portion of the trunk or proximal hindlimbs)
There are several treatment options for soft tissue sarcomas. Ultimately the decision to pursue a particular treatment is based on the tumor location, histologic grade, stage, clients' wishes and consultation with a veterinarian or veterinary oncologist. The following is a list of commonly discussed treatment options:
Option 1 - Surgery
Complete excision with adequately wide margins generally involves resection of approximately 3cm margins laterally and removal of one intact fascial plane deep to the tumor. When these margins can be achieved, surgery is generally considered the treatment of choice.
Option 2 - Surgery + radiation therapy
This involves a combination of surgery to remove the obvious bulk of the tumor (macroscopic disease) + radiation therapy to destroy residual microscopic disease. This combination treatment generally provides a 60-80% chance of controlling the tumor long term. At North Carolina State University , radiation therapy consists of 16 (pre-operative) or 19 (post-operative) treatments given on a Mon-Friday schedule. Potential side effects of radiation include an early, reversible reaction to rapidly dividing tissues (skin, hair) that develops midway through treatment and lasts 2-4 weeks before healing. During this time, patients are treated with anti-inflammatory, analgesic medications and topical medications as needed. There is also the potential, although unlikely, for late irreversible side effects to slowly dividing tissues (bone, muscle, nerves). A CT scan or radiographs are performed prior to radiation therapy to aid the radiation oncologist in planning treatment for the individual animal in a way that optimizes the effect against the tumor and minimizes the impact on adjacent normal tissues.
Option 3 - Chemotherapy
Systemic medication is recommended for dogs with high-grade tumors, given the increased likelihood of metastasis. It may also be considered for patients with incompletely-excised tumors and for whom radiation therapy is not an option or for patients with non-resectable tumors. The drug of choice for treating soft tissue sarcomas is doxorubicin. It is given at 3-week intervals for a total of 4-6 treatments. Chemotherapy drugs work by targeting fast-growing cells; cancer cells divide faster and abnormally compared to normal cells. Because of this, chemotherapy preferentially destroys cancer and spares normal tissues. There is the potential for some normal tissues with rapid growth rates (intestinal lining, bone marrow, hair cells) to be transiently damaged by chemotherapy. However, our goal in treating cancer in animals is quality of life, so the dosages are lower than those used in people, and we do not normally see significant toxicity with chemotherapy. There is always some risk when a drug is given for the first time, and the oncologist will discuss what types of side effects may develop and what to watch for. If the pet has no problems the first time they receive a drug, they should have no problems with subsequent treatments of that drug. If the pet experiences any side effects, we address them as needed and lower the dosage of the causative drug for future treatments to prevent recurrent problems. A unique side effect of doxorubicin is its ability to weaken the heart muscle with multiple doses. A heart ultrasound (called an echocardiogram) is recommended prior to the fourth doxorubicin treatment to monitor for this.
Option 4 - Palliative radiation therapy
If a tumor cannot be removed surgically, cannot be treated with the combination of surgery + radiation therapy, or if distant metastasis is identified, palliative radiation therapy can be considered. Palliative radiation therapy consists of two consecutive twice-daily doses of radiation therapy and is aimed at alleviating pain, inflammation, and swelling associated with the tumor. We recommend that the treatment be repeated in one month if no disease or symptom progression is noted in hopes of extending the duration of response.
We currently have a partially-funded clinical trial investigating physiologic changes associated with hyperthermia. Patient enrolled in this study must have measurable gross disease . The client is responsible for charges associated with initial evaluation and work up. Patients are treated with 25 fractions of radiation therapy and five hyperthermia treatments. The hyperthermia treatments are paid for and clients are given $3000 towards the cost of radiation therapy. Following completion of the radiation therapy and hyperthermia study, surgery or any other treatments can be pursued at the owners' expense.
- Bostock DE , Dye MT. Prognosis after surgical excision of canine fibrous connective tissue sarcomas. Vet Pathol 1980;17:581-588.
- Kuntz CA , Dernell WS, Powers BE, et al. Prognostic factors for surgical treatment of soft-tissue sarcomas in dogs: 75 cases (1986-1996). J Am Vet Med Assoc 1997;211:1147-1151.