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Fibrosarcoma in Dogs

Fibrosarcoma in Dogs

“This cancer is seen most commonly in older male dogs except for a certain variety that is seen in the mouths of younger dogs.”

Fibrosarcoma is a type of cancer that arises from the fibrous connective tissues of the skull, spine, pelvis, and ribs but can arise from any bone. This cancer is a part of a group of tumors that would be termed non-osteosarcomas of bone and can sometimes be very difficult to distinguish from the far more common osteosarcoma. The cause of fibrosarcoma is largely unknown. It is a rare tumor in comparison to osteosarcoma. This cancer is seen most commonly in older male dogs except for a certain variety that is seen in the mouths of younger dogs. Most commonly it affects the bones of the spine, pelvis, and skull but can less commonly affect the legs.

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What to Watch For

  • Signs of lameness or pain especially in the legs
  • Unexplained swelling of any bones
  • Difficulty swallowing and eating
  • Bleeding from the mouth and/or a bad mouth odor


  • Complete physical exam
  • Radiographs (X-rays) of the affected body part
  • Radiographs of the chest/lungs
  • Complete blood cell count (CBC)
  • Biochemistry profile
  • Urinalysis
  • Biopsy of the tumor


  • Surgical removal of the tumor usually involves a resection of the affected bone
  • Radiation therapy can be attempted as an alternate form of pain relief in very select cases
  • Pain medications
  • Chemotherapy to treat the very rare case of spread of the cancer

Home Care

Your veterinarian will likely prescribe pain medications to assure your pet’s comfort prior to definitive diagnosis and/or in the aftercare period from surgery. You should limit activity of your pet to prevent further pain and to prevent what is called a pathologic fracture which is an abnormal breaking of the bone due to weakening by cancer prior to definitive therapy. Your pet should not run jump or play during this time and you should watch him carefully or help him when climbing stairs or getting in and out of the car.

Any unexplained bump, lameness or problems with your pet’s mouth should be promptly evaluated by your veterinarian. Most forms of lameness are likely to be associated with arthritis or injury to ligaments and tendons. Likewise, most problems with your pet’s mouth are related to tooth decay and gum disease rather than cancer. But if your pet is not getting better with rest, anti-inflammatory drugs, or treatment of bad teeth then radiographs of the affected body part should be taken to rule-out bone cancer.

If fibrosarcoma occurs in an area of the body that can be completely removed with surgery the prognosis can be good for 1 to 2 years or more as it is a type of cancer that rarely spreads.