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Synovial Sarcoma in Dogs

Synovial sarcomas are soft tissue sarcomas – malignant cancers – that arise from the precursor cells outside the synovial membrane of the joints and bursa (the fluid-filled, sac-like cavity between joints that helps to facilitate movement). The synovial membrane itself is the layer of soft tissue that lines the surfaces within the joints.

Precursor cells have the ability to differentiate into one or two closely related  forms: epithelial cells (skin cells) or fibroblastic (connective tissue) cells. Therefore, the tumor may have cancer resembling both cancers of the skin and of the connective tissue.

Synovial sarcomas are aggressive and highly locally invasive, spreading in greater than 40 percent of cases. They most often spread to the elbow, knee, and shoulder blade regions.  They are more common in large-breed rather than small-breed dogs.

Symptoms and Types

• Limping
• Slowly progressive lameness
• Palpable mass
• Weight loss
• No appetite (anorexia)

Causes

• Unknown

Diagnosis

You will need to give a thorough history of your dog's health and onset of symptoms. Your veterinarian will then perform a complete physical exam and order standard laboratory tests, including a biochemical profile, a complete blood count, a urinalysis and an electrolyte panel to rule out other non-cancerous causes for your dog's symptoms.

Visual diagnostic techniques will show abnormalities around the affected joints. X-rays of the mass will show that the tumor is involved in both the bone and the joint. To obtain a definitive diagnosis, a biopsy of the soft and bony tissue of the tumor is necessary for histologic evaluation (microscopic analysis of the tissue sample). Using fine-needle aspirates (removal of fluid), the regional lymph nodes (i.e., the lymph nodes of the groin, armpits) should also be sampled and tested for evidence of metastasis (spread).