Clinical Approach to Soft Tissue Sarcoma

Soft tissue sarcomas (STS) comprise a group of tumors that arise from connective tissue and includes fibrosarcomas, hemangiopericytomas, Schwannomas, peripheral nerve sheath tumors and a number of others. The STS do not include hemangiosarcomas, osteosarcoma and others with an expectation of aggressive biological behavior. The STS are characterized by local invasiveness and low rate of metastasis, but metastatic potential increases with increasing grade of the tumor. The STS are graded as either low, intermediate or high grade based on their degree of differentiation, mitotic cell count, and degree of necrosis. While metastasis of low and intermediate grade STS occurs in fewer than 20% of affected animals, the risk of metastasis increases to around 40-50% for patients with high-grade STS. Because of their locally invasive behavior, the management of STS can prove challenging.

Clinical presentation and staging

The STS are commonly seen as masses on the limbs, trunk and in the oral cavity, although they can appear virtually anywhere, including the thoracic and abdominal cavities. Masses may be soft or firm, moveable or fixed, superficial or deep. When masses in dogs or cats are seen, an important and recommended first step for most is fine needle aspiration cytology, results of which can determine the nature of the mass (e.g. mesenchymal or round cell) and guide the amount of normal tissue to be resected to completely remove the mass and lessen the chance of recurrence. For masses that could prove difficult to remove surgically, an incisional biopsy to determine confirm the tumor type and establish tumor grade can help guide the decision-making process regarding treatment as some patients with high-grade STS, because of the higher risk of metastasis, may not be good candidates for aggressive surgical intervention. Staging is important to define the extent of an STS. To rule out metastatic disease, obtaining thoracic radiographs, and if the mass is on a rear limb or in the pelvic area, abdominal ultrasound to examine intra-abdominal lymph nodes is advised. Needle aspiration cytology of lesions can be accomplished in most patients with ultrasound guidance. For patients with high grade STS that are likely to need aggressive surgical resections, CT scans of the thorax to better exclude pulmonary metastasis may be useful. Additional procedures recommended for animals with STS include a CBC, biochemical profile and urinalysis to assess for the presence of other disease that could alter treatment decisions.

Treatment options

The principle treatment for the STS is surgical resection. It is generally accepted that the first attempt at surgery represents the best chance to cure a patient of a STS, so careful surgical planning is warranted prior to resection of an STS. To reduce the chance of recurrence, the STS need approximately 2-3 cm margins of normal tissue. This recommendation includes the deep margins as these tumors tend to not respect fascial planes. Inking all margins of resected tissue can help a pathologist examine tissue margins for neoplastic cells. For some patients, acquisition of deep margins may require removal of muscle or underlying bone, or could lead to serious compromise of function. The STS are well-known for making a pseudocapsule, a rim of compressed tumor and reactive cells that often creates an easy plane of dissection for the surgeon, but frequently leads to removal of the tumor with dirty margins. Depending on the location of the tumor, advanced imaging (ultrasound, computed tomography or magnetic resonance imaging) may be needed to better define the gross margins of the tumor and influence surgical approach. [...]