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June 25, 2019 – Sometimes it starts with a misstep, or subtle lameness. Sometimes it starts with a small lump on the leg that becomes tender to the touch. Sometimes it starts dramatically with a sudden fracture.

Osteosarcoma (OSA) is the most common primary bone of dogs and nearly 10,000 dogs are diagnosed with this cancer each year. The signs of osteosarcoma can be subtle and it’s important for owners to know how to recognize the signs and understand the risk factors for this devastating form of cancer.

Osteosarcoma can affect any dog, but it is most commonly found in:

  • Large and giant dog breeds.
  • Males slightly more than females
  • Young dogs between 18 and 24 months old
  • Older dogs between 7 and 9 years old
  • Long bones of the limbs

Signs of osteosarcoma include:

  • Lameness
  • Swelling
  • Sudden bone fracture

X-rays are very helpful in making a diagnosis and to rule out other common causes of lameness. Unlike bacterial or fungal infections, which can affect both bones of a particular joint, OSA does not cross a joint – this can be a tip-off that a patient has a bone tumor and not an infection.

Despite physical examination findings and X-rays suggestive of cancer, it can still be unclear if a bone abnormality is due to osteosarcoma, a different type of cancer, or another disease simply affecting bone, such as infection. A bone biopsy often is necessary to make a definitive diagnosis and sort out among these possibilities.

The treatment of osteosarcoma almost always begins with amputation of the affected limb. Although many owners are understandably upset and concerned about amputating a limb, most dogs do very well with surgery. Because osteosarcoma is a painful disease, amputation also provides relief from unrelenting discomfort that is hard to control with pain medication alone. However, the prognosis remains poor with surgery alone; 90% of dogs will die of this disease within one year if surgery is the only treatment attempted.

Chemotherapy can help prolong remissions, with some dogs living years after amputation and chemotherapy. But these success stories tend to be the outliers, not the norm, and odds are still poor for long-term survival. Osteosarcoma spreads quickly, usually to the lungs, and nearly 90% of dogs have metastases by the time of diagnosis, even if there are no obvious signs of disease spread.

Morris Animal Foundation has been a leader in trying to find new, innovative therapies to treat osteosarcoma. We recognized that more work needed to be done on all aspects of osteosarcoma, from understanding the basic mechanisms of tumor spread to better treatments. Although we’re making steady progress, we’ve got a long way to go to unlock the secrets of this painful and deadly cancer. Learn more about ways you can help ensure that dogs live healthier, happier and longer lives!