Soft-tissue sarcomas (STSs) account for 15 percent of all skin and subcutaneous cancers reported in dogs. The cause of most sarcomas remains unknown, though trauma, parasites and chemotherapy are all associated with an increased risk. There is no breed that is more prone to sarcomas than another. Synovial (joint) sarcomas occur twice as much in male dogs as female dogs. No other variety of STSs have a gender link.
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Tumors
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STS tumors form from mesenchymal cells. Mesenchymal are the "generic" stem cells that can eventually become specific cells (e.g., bone or blood cells). STS tumors are usually slow-growing, but can sprout suddenly. The tumors are typically firm masses under the skin. STS tumors can appear anywhere on the dog's body, but are most common to the extremities, neck, head or trunk. Most STS tumors occur singly and only metastasize (spread) in about 25 percent of cases.
Diagnosis
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If you find a lump on your dog, you will need to take him to the vet. The vet will perform a physical exam to determine the margin of the tumor. This refers to the vet's ability to feel how well defined the tumor is (i.e., can the vet feel the edges distinctly separate from healthy surrounding tissue). Your vet will also perform a biopsy or a fine-needle aspiration (withdraw fluid from the tumor) to see what cells compose the tumor. The vet might also order a full-body X-ray, CT scan or MRI to check for the presence of tumors inside the body.
Surgery
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The most common treatment for STSs is surgical excision. The surgeon will remove the tumor, along with a generous swath of healthy tissue surrounding the growth. Removing healthy tissue is standard in an attempt to eliminate all cancer cells from the area. If the surgeon successfully removes the complete tumor and any stray cancer cells, your dog might not need further treatment.
Radiation and Chemotherapy
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When surgical removal isn't an option due to the tumor's size or location, radiation is attempted. Radiation is used at the site of the tumor to shrink it, prevent it from growing larger or kill it. Radiation is usually more successful in smaller tumors. Radiation treatment is generally well tolerated by dogs, and the side effects are limited to the area of treatment. They can include skin abrasions and burns.
Chemotherapy is used when the STS tumor is high-grade, meaning it is growing quickly and risks metastasizing to other sites in the body. Chemotherapy might restrict the growth of the tumor or slow its spread, but it isn't a cure for STSs.
Prognosis
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With most STSs, prognosis is very good. If surgery and/or radiation are successful in removing or controlling the tumor, the dog has a 50 percent chance of living at least three more years. The most important element is treating the tumor when it first appears and getting rid of it then. Tumors that regrow are more aggressive, making them more difficult to treat.
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