osteosarcoma

Canine Osteosarcoma (OSA)

Osteosarcoma is the most common primary bone tumor, accounting for over 85% of all the bone tumors that occur in limbs (known as appendicular). It is an aggressive condition in dogs and may also occur in the spine, jaw, skull and ribs. There is no known cause of osteosarcoma. Some possible explanations for the development of OSA include repetitive bone injury, previous fractures, underlying bone disease, viral infections, genetic predisposition and previous radiation, but none of these theories have been proven.

Osteosarcoma occurs primarily in large and giant breeds of dogs. Smaller breeds are 20 times less likely to develop this type of cancer, but it can occur. Size and height seem to be more important risk factors than breed. Most dogs afflicted with osteosarcoma are either young, between 1 and 2 years of age, or older, between 7 and 9 years of age.

Dogs with osteosarcoma tend to develop pronounced swelling of the bone around the site of the cancer. This is often painful, red and hot to the touch. Most develop around the elbow or knee joints, at or near a bone growth plate. This swelling appears on X-rays, but owners should be aware that fungal infections of the bone may produce similar results. Owners should always ask for a biopsy before assuming that a swelling indicates bone cancer. Tumors often produce pain at or around the joint that causes dogs to limp or develop an unusual gait. Nearly all dogs with osteosarcoma will become lame in the affected limb, but most do not show it in the early stage of the disease. Lameness may not be continuous at first, but as the tumor grows, it will become more obvious and more frequent. The lemeness may respond to standard doses of pain killers initially but rarely for more than a week or so. In later stages, osteosarcoma may weaken the affected bone, causing it to become brittle and fracture easily. Dogs with late-stage osteosarcoma may be subject to bone fractures. Even if the tumor has been successfully treated, the bone may remain weak. The majority of canine osteosarcoma cases also suffer from metastasis, or spreading, to the lungs. Unfortunately, lung tumors caused by metastatic bone cancer are generally very small. They may not appear on initial X-rays. Most vets treat all cases of osteosarcoma as metastatic, regardless of evidence, because of this high incidence of metastasis. Advanced lung metastases may result in breathing problems and coughing.

This disease usually develops deep within the bone on one of the legs, usually below the joint. Tumours may be seen near the growth plates, and becomes progressively more painful as it grows outward and consequently the bone is destroyed from the inside out. There may be swelling, and lameness of the affected leg. This disease spreads easily and in many cases the cancerous cells have moved into the lungs by the time of diagnosis.

Treatment usually involves both chemotherapy and amputation directed at removing the primary tumour and the pain associated with it. In effect, slowing and preventing the occurrence of metastatic disease. With amputation on its own, most dogs will have a comfortable life for 4-5 months. Amputation coupled with drug therapy the survuval time is aproximately 6 months with some patients alive after two years. Amputation invariably has a tremendous impact on the state of mind of the patient. While it is clearly a major operation, these patients seem to be so relieved to be free from the pain that they recover extremely quickly. Without therapy life expectancy is approximately 2 months.

In the event that amputation is considered inappropriate there are other options. For osteosarcomas of the distal radius (this is the lower front limb just above the wrist joint equivalent in dogs) an operation can be performed in which the affected piece of bone is removed and replaced by a special implant. Limb sparing surgery is considered as effective as amputation for local disease control but can be expensive and only a few bone tumours based on location and radiographic appearance may be suitable. Following this treatment there is a risk of the cancer returning in the same bone at some point. More importantly, this procedure is associated with a high risk of complications, worst of which is infection associated with the metal implants.

For the patients in which amputation and the so-called limb-conserving surgery are not appropriate, palliative therapy can be administered in the form of radiotherapy (weekly on 3 out of 4 weeks) and chemotherapy in conjunction with the first and final doses of radiation. Other radiotherapy treatment protocols are described and this is an active area of research so it would pay to consult an oncologist if further detail is required. Palliative radiation therapy will never treat nor control the tumor, but it will alleviate pain. Patients receiving palliative radiation and chemotherapy have an average life expectancy of six months.

Metastatic tumor treatment controls include

Cisplatin alone – The median survival time with this treatment is 12 months with 10% of dogs alive 2 years after starting treatment. Cisplatin treatment takes an entire day to administer, but side effects occur in only 10 – 15% of dogs. This treatment is given once every 3 weeks for 4 doses.
Carboplatin alone – This treatment is as effective as the first option, but side effects are very rare with this treatment plan. Carboplatin is given every 3 weeks for 4 – 5 treatments, with an average survival time of about 10 – 12 months.
Alternating carboplatin and doxorubicin – We give 3 carboplatin treatments and 3 doxorubicin treatments in an alternating 3/2 week pattern. Survival times in small studies are similar to carboplatin alone.
Doxorubicin alone – This option gives an average survival time approaching 12 months. The treatment is given every 2 weeks for 5 treatments and an echocardiogram would be necessary before the first and fourth treatment. Some gastrointestinal side-effects can be associated with this treatment. Chemotherapy without primary tumor control is not helpful.

Alternative treatments may include:-

Pamidronate – a “bone hardening” drug given intravenously, is showing some promise in experimental studies as a pain controlling/fracture preventing drug; and also as an adjuvant to chemotherapy and/or radiation.
Triple pain therapy – with an anti-inflammatory, narcotic and neurologic pain blocker all given by mouth at home can improve comfort for several months. Watch for pain, fracture, lethargy and cough as signs of tumor progression

Canine Osteosarcoma Symptoms Provided by eHow.com
http://www.southpaws.com/topics-of-interest/canine-osteosarcoma/

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The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.