Soft-tissue sarcomas (STS) are common for a practitioner to see as they compromise up to 15 percent of all skin tumors in dogs.
The terms spindle-cell tumors and mesenchymal tumors have also been used to describe these tumors. STS are considered to be
a family of tumors given that they are all derived from connective tissues and have a similar biologic behavior regardless
of the histologic type (see Table 1). Histiocytic sarcomas, oral sarcomas, hemangiosarcoma and synovial cell sarcoma are generally
not included given that these tumors have a different biologic behavior.
These tumors are considered to be locally invasive tumors that will grow along tissue planes. Invasion into bone is uncommon.
The potential for metastasis depends on the grade of the tumor with low- to intermediate-grade tumors having a metastatic
rate of less than 15 percent and high-grade tumors having a metastatic rate of up to 45 percent (Kuntz 1997, Selting 2005).
The most common site of metastasis is the lung followed by lymph node.
Most dogs are older to middle-aged with no sex or breed predilection. These tumors present as solitary masses in the subcutaneous
tissues and can occur anywhere on the body (Figure 1). In some cases, these tumors have been present for a prolonged period
of time without changing but some can grow rapidly, particularly if they are high-grade tumors. Typically these tumors are
solid but some can have a fluid component (i.e. myxosarcomas).
Figure 1 Typical appearance of soft-tissue sarcoma in a dog.
Initial therapeutic plan
Initial evaluation should include an aspirate of the mass, thoracic radiographs (three views) and an aspirate of the draining
lymph node if indicated. Radiographs should not be taken under anesthesia if possible as atelectasis of the lung may prevent
identification of smaller lesions. Sarcomas may not exfoliate well, so it is possible for an aspirate to be non-diagnostic.
On cytology, the cells appear as elongated, spindle-shaped cells with indistinct margins and occur singly (Figure 2). If a
sarcoma is suspected but not confirmed on cytology, an excisional or incisional biopsy is indicated. An incisional biopsy
is recommended if the tumor cannot be easily excised with a wide margin.
Figure 2 Cytologic appearance of a soft-tissue sarcoma. Cells are spindle shaped with indistinct margins.