Dog Cancers: Osteosarcoma

Osteosarcoma (malignant bone tumor) is one of the most common types of tumors in dogs.  It most commonly affects large breed dogs and the bones of the legs, also termed the extremities.  It is a very aggressive form of cancer, but many dogs can be helped greatly with treatment.

Osteosarcoma signs and symptoms

Most dogs with osteosarcoma present with pain at the site of the lesion.  Since the tumor most commonly affects bones of the leg, most dogs present with lameness.  The tumor causes small fractures and bleeding that can cause pressure on the nerve endings on the surface of the bone.  This results in pain.  At times, the tumor can cause a complete fracture of the bone, which requires immediate treatment.  The tumor can also affect the bones of the spine causing back pain or even paralysis or other neurological dysfunction.

Osteosarcoma pre-treatment work-up

Dog Cancers: OsteosarcomaPrior to treatment of a dog with osteosarcoma, a diagnosis needs to be made.  A diagnosis of osteosarcoma is typically made with radiographs (x-rays) of the affected site and obtaining a tissue sample.  Sometimes, tissue samples can be obtained with a needle aspirate, in which cells are placed on a glass slide and looked under the microscope.  This is a relatively quick procedure that can be done with or without light sedation.  When this is not possible, a biopsy instrument called a needle-core biopsy instrument (Jamshedi) is used.  Typically, the animal has to be anesthetized for this procedure.  The tissue is placed in a preservative solution of formalin and sent to the lab where sections of the tissue are sliced and looked under the microscope.

Additional tests that are recommended include thoracic radiographs to screen for spread of the cancer (metastasis) to the lungs.  Although osteosarcoma is a highly metastatic tumor, only 10% of dogs with the disease have obvious evidence of spread of the cancer to the lungs that can be observed with radiographs.  Dogs with radiographically detectable lesions at the time of diagnosis do very poorly and tend to survive less than 2 months with their disease.   It is important to understand that dogs without obvious evidence of metastasis to the lungs do have it present microscopically. Without chemotherapy, most dogs will develop radiographically detectable lung lesions within 4-6 months.

Additional tests that are recommended include a complete blood count (CBC) serum biochemistry profile, and urinalysis.  This is primarily recommended to screen for other health issues prior to making decisions regarding treatment.  Some studies have shown that dogs with an elevation of the alkaline phosphatase enzyme do not survive as long with treatment for osteosarcoma compared to dog with normal levels of the enzyme.

Click here for useful information about treatments for osteosarcoma and ongoing clinical trials for new therapies.

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Dr Stephen Atwater

Stephen W. Atwater, DVM, MS, Diplomate ACVIM (oncology) is a board-certified veterinary oncology specialist. His professional interests include utilizing emerging therapies for difficult to treat cancers.

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