Bone tumors (osteosarcoma) in cats and dogs.

Osteosarcoma (Bone Cancer) in Cats and Dogs

What are bone tumors?
Bones are rigid organs that form part of the skeleton and function to move, support, and protect the various organs of the
body, produce red and white blood cells and store minerals. The most common bone tumor is called osteosarcoma, which
usually affects older dogs or giant breed dogs but has been observed in younger dogs as well. Osteosarcoma seems to be
rare in cats. Osteosarcoma is an aggressive cancer that can develop in any bone of the body but the majority is seen in
the limbs (eg elbow or the knee) where it is referred to as "appendicular osteosarcoma." This is a very aggressive tumor
that can cause lysis (disintegration of bone) and/or bone production, and it becomes more painful as it progresses. The
lameness goes from intermittent to constant over 1-3 months. Obvious swelling becomes evident as the tumor grows and
normal bone is replaced by the cancerous growth.

For osteosarcoma occurring in the oral cavity (mouth), please visit the "Oral Osteosarcoma" section.

Common sites for development of bone cancer.
Source: www.marvistavet.com/assets/images/Osteosarcoma_dog.gif

How common are osteosarcomas in cats and dogs?
Osteosarcoma is estimated to occur in more than 8,000 dogs each year in the United States, but the actual number may
be higher since not all cases are reported. There is a large range in the age of onset. Osteosarcoma typically affects
middle-aged to older dogs with a median age of 7 years, however, osteosarcoma in the rib tends to occur in younger adult
dogs with a mean age of 4.5 to 5.4 years. Increasing weight and height appear to increase the risk of osteosarcoma. The
breeds with the highest risk are Saint Bernard, Great Dane, Irish setter, Doberman pinscher, rottweiler, German shepherd,
and golden retriever.

What are the symptoms of bone cancer?
Dogs with limb osteosarcoma typically show lameness and swelling at the affected site. The cancer-stricken bone is not as
strong as normal bone and can break with minor injury. This type of broken bone is called a “pathologic fracture”, and
account for less than 3% of all fractures. The symptoms osteosarcoma in sites other than the limbs will largely depend on
the exact location. There may be lameness, local swelling, difficulty to open the mouth (if jaw bone cancer), nasal
discharge (if nasal cavity bone cancer) or neurological signs (if spine bone cancer).

How is the diagnosis made?
The initial evaluation of possible osteosarcoma involves X-rays of the affected site. The X-rays often reveal a characteristic
bone pattern that, combined with history and breed, may indicate the presence of an osteosarcoma. While the history,
physical examination and X-ray findings may all point to the diagnosis of osteosarcoma, the only way to confirm the
diagnosis is by tissue biopsy.

Source: www.dogcancer.net/images/osteo.12.jpg

Does cancer cause pain in pets?
Osteosarcoma becomes progressively more painful as the tumor grows and the bone is destroyed from the inside out. The
dogs will generally show signs of intermittent lameness that becomes more frequent and eventually constant within 1-3
months. Removal of the affected limb (amputation) resolves the pain in all the cases although some pet owners choose not
to undergo the procedure due to concerns about the pet's quality of life (see below section).

In addition to pain caused by the actual tumors, pets will also experience pain associated with cancer treatments such as
surgery, radiation therapy or chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from
the illness, treatment or injury. It is, therefore, essential that veterinary teams that are taking care of pets with cancer
should also play a vital role in educating pet owners about recognizing and managing pain in their pets. The best way to
manage cancer pain in pets is to prevent it, a term referred to as preemptive pain management. This strategy anticipates
pain ahead of time and administers pain medication before the pet actually experiences pain, thus ensuring the pet's
maximum comfort.

To learn more about which tumors are likely to cause a lot of pain, how to recognize pain in pets with cancer and what
cancer pain management options are available for your pet, please visit the Cancer Pain Management section.

How important is nutritional support for pets with cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of
the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the Cancer Nutrition section.

How do I find a qualified veterinary oncologist?
To locate a qualified veterinary oncologist in your area who can discuss with you appropriate cancer treatment plan for
your pet's cancer condition, please visit the "Locate a veterinary oncologist" section.

What evaluation is needed for a pet with bone cancer?
In order to prepare a treatment plan for the pet, it is important to evaluate whether the cancer has spread to other organs.
Osteosarcomas are known to metastasize to the lungs so chest X-rays are typically done to check if such spread occurred.
Recently, advanced imaging techniques such as CT and MRI are being used to assess lung metastases and to evaluate
the pet's condition in more detail. To assess whether osteosarcoma is present in additional bone sites, the veterinarian will
conduct bone survey X-rays, which include all bones in the body. The malignant growth in the bone may also be due to
cancer that spread from other parts of the body. Common sites for these metastases are the lumbar and sacral vertebrae,
pelvis and the shaft of long bones. Assessment of the overall health and any co-existing medical conditions is critical to
determine appropriate course of treatment. For example, prolonged anesthesia and chemotherapy may not be well
tolerated by pets whose organs do not function well or who suffer from certain heart conditions.

What are the treatment options for osteosarcoma?
Depending on your pet's unique condition, there are several treatment options, including surgery, chemotherapy and
radiation. There are also some clinical trials exploring new ways of treating osteosarcoma (listed at the end of this section).

Surgery
The options for appendicular (limb) osteosarcoma are to either amputate the cancer-stricken leg or try to treat the leg
without amputation. Amputation of the diseased limb is the standard local treatment and dogs will usually function well.
Dogs with severe preexisting orthopedic or neurological conditions may not be good candidates for amputation and in
these cases, the veterinarians will perform the limb sparing surgery. There are many surgical methods to spare the limb, all
of which are complicated and require the coordination of several doctors, including the surgeon, oncologist, radiologist,
and pathologist.

Chemotherapy
Chemotherapy is administered to pets following amputation to kill any remaining cancer cells that might have escaped from
the bone tumor. There are several commonly used chemotherapeutic agents such as cisplatin, carboplatin, doxorubicin,
lobaplatin and OPLA-Pt.

Radiation
Currently, the role of radiation therapy in dogs with appendicular (limb) osteosarcoma is reserved primarily for relieving
bone pain and discomfort rather than cure. Stereotactic radiosurgery (gamma knife therapy) is a new procedure adapted
from human studies that precisely delivers radiation therapy to tumors while avoiding normal tissues. The advantage of this
technique is the ability to avoid surgery but unfortunately, it is not widely available yet.

What are the treatment associated risks?
There are side effects associated with chemotherapy, however, the risk of toxicity may be outweighed by its benefits in
many cases. The side effects will differ for each drug and your veterinarian should spend time going over these depending
on which chemotherapy protocol (s)he will deem appropriate.

Are there any clinical trials investigating new treatments for dogs or cats with osteosarcoma?
There are some available clinical trials investigating new treatments for bone cancer in pets, which are either fully or
partially funded by the institutions. To learn more about these clinical trials, please visit the Clinical Trials for Dog B one
Cancer section.

Additionally, there are several clinical trials available for cats and dogs with any tumor type for which your pet may qualify.
To learn more these trials (which are partially or fully funded by the institutions), please visit the Dog Clinical Trials (any
tumor type) or C at C linical Trials (any tumor type ) section.

To learn more about veterinary clinical trials in general, please visit the Pet Clinical Trials section.

What is the prognosis for osteosarcoma in cats and dogs?
The prognosis of a pet diagnosed with bone cancer will depend on several factors such as the location of the tumor(s), the
extent of the disease, whether it spread to other organs and the overall health of the pet. In general, pets whose cancer
has spread to other organs have a very poor prognosis compared to those with local disease. Several studies indicate that
dogs with limb osteosarcoma whose blood tests showed increased levels of serum alkaline phosphatase tend to face
poorer prognosis

What is the quality of life for my pet after amputation?
Having a leg amputated due to osteosarcoma does not have to diminish quality of life for your dog but will depend on your
individual dog. If you would like to hear the story of other owners whose pets underwent amputation and the life after,
please visit Tripawds.com. Tripawds is a three legged tripod dog resource and help center where people share their story
and learn from others about amputation for dogs and life after.

Additional online resources:

Sources:

www.marvistavet.com/osteosarcoma.pml
Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998.