Bone Cancer (Fibrosarcoma) in Dogs

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Fibrosarcoma of the Bone in Dogs

Fibrosarcoma is a result of the abnormal division of fibroblast cells – the cells that are most prevalent in the connective tissue of the body, and normally this type of tumor originates in the soft tissue. In some rare cases, however, a fibrosarcoma tumor originates in the bone, weakening the structure of the bone, and possibly leading to fractures, and even amputation of the limb. In most cases fibrosarcoma of the bone is benign and non-metastasizing, but there are cases where the tumor is malignant and metastasizes throughout the body, into the organs, lymph nodes and skin.

Clinically, fibrosarcoma of the bone is similar to osteosarcoma, a more common form of bone cancer. The main differences are in the make-up of the tumors. Where an osteosarcoma is made up of bone material, a fibrosarcoma is made up of fibrous collagen material. Fibrosarcoma is confirmed when a biopsy of the tumor shows no production of bone material. The rapidly dividing nature of a sarcoma is the real danger, as it invades and threatens the stability of the bone. In general, tumors of the bone are benign, and are frequently misdiagnosed as cysts and muscular problems.

Age, breed or gender dispositions have not been determined for this diseased condition.

Symptoms and Types

There are two main types of fibrosarcoma of the bone:

Central fibrosarcomas:

  • Appear in the long bones, vertebral column, and mandible

Periosteal fibrosarcomas:

  • Appear in the skull bones


  • Loss of motion and inability to walk
  • Mass can be palpated (examined by touch) at the affected bone
  • Swelling at the site
  • Swelling of the face when tumor originates in the skull bones
  • Pain when area is touched
  • Fractures of the bone without other evidence of trauma


The exact cause for fibrosarcoma of the bone is still unknown.


You will need to give a thorough history of your dog's health, onset of symptoms, and possible incidents that might have led to this condition, such as any accidents or illnesses, and your dog's regular exercise routine. The more detail you can provide, the better equipped your veterinarian will be to diagnose the condition. Standard laboratory tests include urinalysis, a complete blood count, and a chemical blood profile.

The presence of higher than normal white blood cells can indicate that the body is warding off a diseased condition, and the other tests will show whether the organs are functioning well. Often, however, laboratory tests will return as normal. Because of the relative rarity of a fibrosarcoma of the bone, unless an x-ray image is taken it may be diagnosed as a cyst or a swelling in the muscle. Therefore, an x-ray examination will be an important factor in the definite diagnosis. X-rays will also help to diagnose the exact location of the primary tumor, as well as detecting whether there has been metastasis to other parts of body. A computed tomography (CT) scan is another useful diagnostic viewing tool that may help in determining the extent of problem.

For a more conclusive diagnosis, a biopsy of the tumor will need to be taken for analysis. A biopsy of the bone is a more invasive procedure than most, but this is the only way to confirm whether a tumor is benign or malignant. Your dog will need to be anesthetized for this procedure.

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A neoplasm made up of bone, malignant in nature


The prediction of a disease’s outcome in advance


An in-depth examination of the properties of urine; used to determine the presence or absence of illness


The growth of pathogens away from the original site of the disease


A type of neoplasm that occurs in connective tissue


Something that becomes worse or life threatening as it spreads


Not being able to cause harm; the opposite of malignant.


The process of removing tissue to examine it, usually for medical reasons.

lymph nodes

Small structures that filter out the lymph and store lymphocytes


The process of removing all or part of a body part; usually refers to a limb (arm or leg) and is done for medical reasons.


The term for the lower jaw bone; this is the only bone in the skull that has the ability to move

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