Managing soft-tissue sarcomas in dogs and cats (Proceedings)
Soft tissue sarcomas (STS) – hemangiopericytoma, fibrosarcoma, neurofibrosarcoma, Schwannoma, peripheral nerve sheath tumor, malignant fibrous histiocytoma, liposarcoma, myxosarcoma, myxofibrosarcoma, spindle cell sarcoma, anaplastic/undifferentiated sarcoma – exhibit similar biological behavior, and hence can be dealt with in most cases with a similar therapeutic approach. Although these tumors are classified as malignant, their metastatic rate is generally low. However, due to a high degree of local infiltration, recurrence after conservative excision is common.
Most animals with STS will present with the complaint of a palpable mass. Occasionally, the presenting complaint may be pain or lameness, or a mass may be detected during a routine physical examination. These masses can occur anywhere on the body, and are usually solitary. They are often firm and can be poorly demarcated. If large, they may be adherent to deep structures and hence not freely movable. Most will be covered by normal appearing haired skin, but some may be ulcerated, or have a softer central area of necrosis.STS may sometimes be tentatively diagnosed based on the results of fine needle aspiration cytology. Given that cells from STS may exfoliate poorly, it may be helpful to use a larger gauge needle (e.g. 18-20g) or employ suction from a 5 or 10-cc syringe if other techniques do not yield an adequate sample. A nondiagnostic sample or the presence of large amounts of blood should be an indication for further evaluation. Cytology of sarcomas will reveal a population of cells exfoliating individually or in disorganized clumps, often admixed with varying amounts of peripheral blood. The cells appear spindle-shaped, and may have trailing cytoplasmic extensions. Nuclear: cytoplasmic ratio is often high, and the nuclei may contain multiple variably sized nucleoli.
If needle aspiration cytology is insufficient to suggest STS, excisional biopsy may be performed if the mass is small and in a surgically accessible area. Alternatively, an incisional (e.g. wedge, punch, or needle-core/Tru-cut) biopsy may be used to attain a histodiagnosis and aid in the planning of further treatment. Many times, Tru-cut or punch biopsies can be obtained using local anesthetic or mild chemical restraint.
Although the metastatic rate of STS is low (generally less than 10% - see exceptions below), it is not zero. Metastatic rate may be somewhat higher (25-45%) in the poorly differentiated STS (anaplastic or undifferentiated), and potentially in liposarcomas, and in sarcomas in younger dogs. Tumors considered histologically "high grade" or "grade III" based on their microscopic appearance may likewise have a higher metastatic rate. Similarly, feline vaccine-associated sarcoma may have a metastatic rate between 5 and 25%, with recurrent tumors perhaps more likely to metastasize. The majority of histiocytic sarcomas in dogs are capable of metastasis. Thoracic radiographs should be offered in any STS case, especially prior to undertaking an aggressive or expensive procedure. These types of tumor metastasize infrequently through the lymphatic system. However, any enlarged lymph nodes should unquestionably be investigated cytologically for evidence of metastasis. Abdominal ultrasound should be offered for known histiocytic sarcomas, as involvement of liver and spleen is common. Standard preanesthetic tests should be performed as for any other surgical procedure.