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Spindle Cell Tumors in Dogs

| Updated September 26, 2017

Spindle cell tumors in dogs arise from the connective tissues of the body. Also referred to as soft tissue sarcomas or mesenchymal tumors, they most commonly arise just under the skin. Spindle cell tumors may arise from a variety of different tissues. As a general rule, spindle cell sarcomas are locally invasive at the site where they occur, but they have a low rate of spread.

Clinical Presentation

All dog breeds can be affected by spindle cell sarcomas. Affected dogs often present a mass or swelling under the skin on the body, limbs or head. These tumors are usually not painful, but some may grow to sizes that cause irritation to the skin over the tumor. Sometimes tumors that have been present for years suddenly begin growing in size. Such a circumstance should prompt a visit to your veterinarian.

Diagnostic Tests

One test your veterinarian may conduct is a needle aspirate, which suctions cells into a syringe. However, spindle cell tumors are known for not shedding cells very readily, so the aspirate may not yield results.

A more accurate test is a biopsy, in which a small sample of tissue or the entire tumor is removed and submitted for analysis. A biopsy will diagnose the tumor type and assign a grade to the tumor. The tumor grade indicates how likely a tumor is to spread to other locations in the body such as the lungs. While low- and intermediate-grade tumors spread less than 25 percent of the time, up to 40 percent of high-grade tumors do spread, or metastasize.

Treatment Options

The most common initial treatment for spindle cell tumors is surgery to remove the mass. These tumors can grow extensions into surrounding tissue, so it is necessary to remove a wide margin of tissue around the mass to ensure it is completely eliminated. Spindle cell tumors will commonly grow back in the same location if they are not removed completely by surgery.

If a veterinary surgeon cannot remove tumors completely due to location, other treatment options your veterinarian may recommend include radiation therapy and medication to prevent or slow tumor growth. Since high-grade tumors are more likely to spread to other locations in the body, chemotherapy is often recommended to delay the onset of metastasis.

Expected Outcome

Fortunately, many dogs diagnosed with spindle cell sarcomas that undergo treatment will have long survival times. In fact, dogs whose low- or intermediate-grade spindle cell sarcomas are completely removed with surgery are expected to have a normal life span. Dogs diagnosed with high-grade tumors that are treated with surgery and chemotherapy live for approximately one to two years.

In contrast, tumors that are not treated with any of these methods may grow to a size large enough to cause a problem within months of the diagnosis by your veterinarian. Your veterinarian will make the best recommendation for treatment based on the type, location and grade of your dog's tumor in order to achieve the best outcome.


  • Any mass has the potential to be malignant. Inform your veterinarian of any new masses that you find on your dog so the appropriate diagnostic test can be performed.