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Soft Tissue Sarcoma in Dogs

What is a soft tissue sarcoma?

Soft tissue sarcomas are a group of malignant cancers that arise from the skin and subcutaneous connective tissues, such as fat, muscle, cartilage, fibrous connective tissue, nerves and the “pericytes” of small blood vessels in the subcutis. These tumors are often considered collectively because of their similarity in clinical behavior.

Soft tissue sarcomas may arise from any site. They tend to appear discrete and well encapsulated, but are actually very invasive into the surrounding tissues. As such, local regrowth of the tumor is common after conservative surgical removal. Soft tissue sarcomas are graded low, intermediate or high grade. Most are low to intermediate grade and have a relatively low chance of spreading.

How are soft tissue sarcomas diagnosed?

A fine needle aspirate is an easy, non-invasive test that can often confirm the presence of a sarcoma. A biopsy may be necessary if fine needle aspirates are non-diagnostic. Biopsies can also be used to classify the specific type of soft tissue sarcoma.

Once a diagnosis is made, staging is recommended to rule out the spread of the disease and to evaluate your pet’s overall health. Staging for sarcomas typically involves:

  • Chest radiographs
  • Abdominal ultrasound
  • Evaluation of regional lymph nodes
  • Blood work

How are soft tissue sarcomas treated?

  • Surgery is the mainstay treatment for soft tissue sarcomas. Surgical excision must be wide and deep in order to remove all of the tumor tissue. When tumors are excised surgically with “clean” surgical margins, no further treatment may be necessary. If the tumor was not removed with adequate margins, a second surgery may be recommended to ensure adequate removal of all tumor cells.
  • Radiation therapy is used to prevent or delay regrowth of the tumor. Side effects are transient and limited to the site where radiation therapy is performed. Radiation therapy may also be used for large tumors that cannot be surgically removed.
  • Chemotherapy is often recommended for high grade sarcomas to prevent or delay the onset of metastasis. It may be given alone or combined with other chemotherapy drugs.

What is the prognosis?

Soft tissue sarcomas that are low to intermediate grade and can be removed completely with aggressive surgery have an excellent long term prognosis. Control rates for low grade soft tissue sarcomas that are incompletely excised and followed by radiation therapy are also very good. Approximately 85% of these patients are tumor free three years after treatment. By comparison, the majority of dogs with incompletely excised soft tissue sarcomas that receive surgery without follow-up radiation will regrow by one year.

For high-grade sarcomas, the long-term prognosis is more guarded. Chemotherapy is indicated to help delay the onset of metastasis, however, the median survival time for these patients is approximately one year.

The best time to treat a soft tissue sarcoma is the very first time it occurs.