Hemangiosarcoma is a type of cancer that arises from blood vessels and can occur almost anywhere in the body. It is a highly metastatic form of cancer, meaning it spreads readily to other tissues. Usually when hemangiosarcoma occurs in bone it is due to metastasis from another site, although rarely, it may actually arise in the bone; the bone is then referred to as the primary site.

This tumor affects the bone much more rarely than osteosarcoma, but when it occurs in bone it can sometimes be very difficult to distinguish from the osteosarcoma. The cause of hemangiosarcoma is largely unknown. In people this type of cancer has been linked to exposure to vinyl chloride, a chemical agent.

The bone form of hemangiosarcoma is rare in cats, but can occur as a local extension of tumors of the soft tissues. It can affect the axial skeleton, which includes the bones of the spine, pelvis and skull, as well as the appendicular skeleton, which includes the arms and legs.

This is a lethal form of cancer in your pet. Average survival rate in animals with this type of cancer, even with treatment, is only months. In most cases, the tumor has already spread widely or will spread widely throughout the body, despite therapy and will continue to grow. When it primarily affects the bone, it can cause lameness and general debilitation of your pet during its development and progression.

What to Watch For

Lameness or pain, especially in the legs

Unexplained swelling of any bone

Broken bones without severe trauma

Bleeding

Diagnosis

Diagnostic tests are necessary to diagnose the tumor and define the extent of disease. Tests that your veterinarian may wish to perform include:

Complete medical history and physical exam

Radiographs (X-rays) of the affected body part

Radiographs of the chest/lungs

Abdominal (belly) radiographs

Abdominal ultrasound

Cardiac (heart) ultrasound

Complete blood cell count (CBC)

Biochemistry profile

Urinalysis

Biopsy of the tumor

Treatment

Treatment may include the following:

Surgical removal of the tumor, which usually involves removing the affected bone

Pain medications

Chemotherapy

Radiation therapy as an alternate form of palliative treatment for pain relief in very select cases

Home Care and Prevention

Your veterinarian will most likely prescribe pain medication to ensure your pet's comfort. These medications may be given prior to definitive diagnosis and/or after surgery. Medication will usually be in the form of pills or narcotic pain patches that are placed on the skin to release a constant level of medication across the skin.

You should limit your cat's activity to minimize pain and to prevent what is called a pathologic fracture, which is an abnormal breaking of the bone due to the cancer weakening the bone. Your pet should not run, jump or play during this time. You should watch your cat carefully and give assistance when he climbs stairs.

Have your veterinarian evaluate promptly any unexplained bump or lameness that develops. Lameness is more likely to be associated with arthritis or injury to ligaments and tendons than cancer, but it is worth having your cat evaluated nonetheless.

If your cat does not improve with rest or anti-inflammatory drugs, radiographs of the affected part of the body may be indicated to exclude bone cancer as a cause of the lameness or pain.

Hemangiosarcoma, like other cancers, is not currently preventable.