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Bone Cancer in Dogs

Bone cancer in dogs can cause lameness, swelling, and intense pain. Surgery and chemotherapy combined are the best treatment options. Get information on the symptoms, causes, and conventional treatment of dog bone cancer here.

German Shepherds

Canine osteosarcoma is the most common form of bone cancer in dogs. It is estimated to occur in more than 8000 dogs each year in the USA. It is mostly found in the legs and arms (appendicular skeleton). In 75% of all cases, osteosarcoma starts in the long bones of the legs, most often affecting only one single leg. Osteosarcoma can also occur in other parts of the body, such as the spine, ribs, jaw, and skull.

The tumors grow within the bone itself, causing the bone to expand.

Osteosarcoma is very aggressive and is known for local invasion, where the tumor sends cells out into the surrounding bone. It usually grows very quickly, and can cause bone disintegration and/or bone production. Bone cancer in dogs can become very painful within just a few months.

Osteosarcoma is also known for metastasis, especially "micrometastasis" (it means tumor cells have spread but due to their small size they are invisible on x-rays or blood tests). Most cases of canine osteosarcoma (about 90%) have undergone micrometastasis by the time they are diagnosed, making this type of cancer difficult to cure.

Dog bone cancer occurs more frequently in middle-aged to older dogs (average age is 7 years), although osteosarcoma in the rib tends to occur in younger adult dogs.

Causes of Bone Cancer in Dogs

As in all cancers, the exact cause of bone cancer in dogs is not known. However, there are a few risk factors that can trigger development of this cancer in dogs:
  • Breeds: Large breed dogs are more prone to canine osteosarcoma - dogs weighing 75 pounds or over are more than twice as likely to get bone tumors than those weighing less. The bigger the dog, the higher the risk of developing bone cancer.

    Breeds with the highest risk are the Saint Bernards, the Great Danes, Irish setters, Doberman Pinschers, Rottweilers, German Shepherds, and Golden Retrievers.
  • Gender: The risk of bone cancer is slightly higher in male dogs than females.
  • Neutering or Spaying: Surgical sterilization of purebred dogs, especially Rottweilers, also increases the risk of bone cancer. In a study, it was found that castrated purebred dogs were twice as likely to develop osteosarcoma than dogs that had not been neutered. For dogs spayed or neutered before one year of age, the risk seems to be even higher.
  • Prior Injuries: Osteosarcoma tends to occur in areas which have sustained prior injuries, such as bone fractures, or even bullets lodged in the bone. Sometimes, a previous infection can also trigger osteosarcoma.

Symptoms of Bone Cancer in Dogs

Depending on where the cancer occurs, the signs and symptoms of bone cancer in dogs vary and can be non-specific.

One of the hallmark signs of canine osteosarcoma in the limb is pain, causing lameness. As the tumor continues to grow, the bone containing the tumor will expand and this can be felt as a swelling, especially if the tumor occurs in bone without a lot of muscles around it, such as within the lower legs.

In advanced cases, the bone will become weak at the site of the tumor, causing it to fracture even with minor normal weight-bearing activities like walking.

Other symptoms may arise as a result of the pain caused by the tumor, such as:

  • Reluctance to exercise or play
  • Lethargy
  • Behavioral changes (e.g. sudden aggression)
  • Appetite loss
  • Weight loss

Symptoms of osteosarcoma in sites other than the limbs depend on the location affected. For example, osteosarcoma that occurs in the skull or facial bones can cause local facial swelling, trouble opening the mouth and swallowing, and nasal discharge.

Dogs with osteosarcoma in the ribs can have a hard lump in the chest area on the affected rib.

Diagnosis of Bone Cancer in Dogs

Diagnosis is usually based on an evaluation of all the clinical signs, a physical examination and X-rays of the affected site. The X-rays often reveal a characteristic bone pattern that, combined with history and breed, may point to bone cancer.

Various other tests (such as chest X-rays, blood and urine tests) will also be given to see if metastasis (spreading of the cancer to other parts of the body) has occurred.

Conventional Treatment of Bone Cancer in Dogs

  • Surgery: The conventional treatment of choice for bone cancer in dogs that occurs in the limbs is surgery (amputation of the affected limb). Surgery can not only remove the tumor (thus preventing it from spreading), but also lessen the pain caused by the tumor and the threat of bone fractures. However, surgery can only be effective if the cancer has not spread to other parts of the body.

    Survival time after amputation is approximately 4 to 5 months. About 11% of these dog patients can live for one year, and about 2% will survive 2 years.
  • Chemotherapy: Chemotherapy is most useful when combined with surgery. Common drugs used include cisplatin or carboplatin. When combined with surgery, either of these drugs increases the survival time to about 6 to 13 months after surgery.
  • Palliative Radiation: Radiation therapy in dogs with osteosarcoma is used primarily to relieve pain rather than cure. It can reduce the pain and discomfort of about 83% of dogs.
  • Limb-Sparing Surgery: Limb-sparing surgery involves removing the bone and putting in either a metal plate or a piece of bone from a bone bank. The procedure can be done if the affected limb is the front leg, down by the wrist joint.

    In up to 28% of limb-sparing procedures, tumors re-grow in the remaining bone. This tumor recurrence rate can be significantly decreased if a sponge-like material containing the chemotherapy drug cisplatin is added right into the surgery site during the procedure. This sponge-like material is called OPLA-Pt (open-cell polylactic acid that contains platinum). It slowly delivers the drug into the bloodstream and works on any cancer cells that may have re-grown or left unremoved.

Possible New Drugs for Bone Cancer in Dogs

  • Pamidronate: At Cornell University, research is being done to explore the use of pamidronate to control pain caused by osteosarcoma. Pamidronate is one of a group of drugs called bisphosphonates, which block bone breakdown. Besides controlling pain, they may also have anti-tumor effects and help block tumor spread by disrupting the formation of new blood vessels which are used by tumors to feed themselves.
  • Artemisinin: This is an ancient Chinese herb that has been used in Asia for years to cure malaria, and seems to be effective in treating osteosarcoma.

    Cancer cells contain a high amount of iron which they need to reproduce their DNA during cell division. They bring the iron in through small "gates" in their outer cell membranes. Artemisinin can enter the cells and react with the iron, forming free radicals within the cancer cells and destroying the cells from the inside out, while posing little or no danger to the normal cells.

    Artemisinin does not seem to be contraindicated with chemotherapy and the two treatment protocols can be used together. Artemisinin may also be used before radiation treatments. However, it should NOT be used within 20 days of radiation. In addition, usage of the herb should NOT be resumed until two months after the last radiation treatment.

    However, artemisinin may cause neurological side effects in dogs when given in high doses, and it may lessen the effectiveness of some seizure-control drugs. Therefore, it should not be used without professional supervision. If you are interested in using artemisinin as part of the treatment for your dog's osteosarcoma, be sure to discuss with your vet first.
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