ANSWERING YOUR QUESTIONS ABOUT OSTEOSARCOMA IN DOGS
Usual sites for osteosarcoma development
WHAT IS OSTEOSARCOMA?
Osteosarcoma is by far the most common bone tumor of the dog, usually striking the leg bones of larger breeds. Osteosarcoma usually arises in middle aged or elderly dogs but can arise in a dog of any age with larger breeds tending to develop tumors at younger ages.
HOW DO WE KNOW MY DOG REALLY HAS AN OSTEOSARCOMA?
WHAT IF IT ISN’T REALLY AN OSTEOSARCOMA?
The location and radiographic appearance of the osteosarcoma in the limb are quite classic but there are a few outside possibilities that should at least be mentioned. There are only a few other possible conditions that cause lytic lesions in bone: the chondrosarcoma, or the squamous cell carcinoma, or the synovial cell sarcoma.
CHONDROSARCOMA: Chondrosarcoma is a cartilage tumor, possibly not as malignant as the osteosarcoma. The chondrosarcoma generally occurs on flat bones such ribs or skull bones and is not usually found in the limbs. Still, should a chondrosarcoma occur in the limb, treatment recommendations would still include amputation of the affected bone and biopsy of the tissue after amputation would allow for any adjustments in chemotherapy.
SQUAMOUS CELL CARCINOMA: The squamous cell carcinoma is a tumor of the external coating of the bone (called the “periosteum”). This is a very destructive tumor locally but it tends to spread relatively slowly. Again, a bone suspected of malignant tumor should be amputated and the tissue then analyzed and treatment adjustments made thereafter. The squamous cell carcinoma tends not to arise in the same bone areas as the osteosarcoma; it tends to arise in the jaw bones or in the toe bones.
SYNOVIAL CELL SARCOMA: This is a tumor of the joint capsule lining. It’s hallmark is that it affects both bones of the joint. The osteosarcoma, no matter how large or destructive it becomes, will never cross over to an adjacent bone.
FUNGAL BONE INFECTION: immitis is a fungus native to the Lower Sonoran Life Zone of the South West U.S. It is the infectious agent of the disease called “San Joaquin Valley Fever ” or just plain “Valley Fever”. (More scientifically, the condition is called “coccidiodomycosis.”) (More scientifically, the condition is called “coccidiodomycosis.”) In most cases, infection is limited to a few calcified lymph nodes in the chest and possibly lung disease. In some rare cases, though, the fungus disseminated through the body and can cause a very proliferative bone infection. The bone infection of coccidiodomycosis is proliferative and lacks the lytic lesions that are so typical of the osteosarcoma.
The bottom line is that bone malignancy should be treated with amputation followed by adjunctive treatment. What the adjunctive treatment is, depends on what the bone tumor is.
TREATMENT OF OSTEOSARCOMA INVOLVES TWO ASPECTS:
HOW DO WE TREAT THE PAIN?
Keep in mind that dogs are usually euthanized due to the pain in the affected bone. Treating the pain successfully will allow a dog to live comfortably.
Amputation of the Limb: Removal of the affected limb resolves the pain in 100% of cases. Unfortunately, many people are reluctant to have this procedure performed due to misconceptions.
Here are two videos of dogs with amputated legs: one the back leg, the other the front leg:
Limb-sparing Surgery: Limb-sparing Surgery: Limb-sparing techniques developed for humans have been adapted for dogs. To spare the limb (and thus avoid amputation), the tumorous bone is removed and either replaced by a bone graft from a bone bank or the remaining bone can be re-grown via a new technique called bone transport osteogenesis. The joint nearest the tumor is fused (i.e., fixed in one position and cannot be flexed or extended.)
Radiotherapy for Pain Control: Radiation doses can be applied to the tumor in three doses (the first two doses 1 week apart, the second two doses 2 weeks apart.) Improved limb function is usually evident within the first 3 weeks and typically lasts 4 months. (Our local oncologists report a range of 0 to 19 months.) When pain returns, radiation can be re-administered for further pain relief if deemed appropriate based on the stage of the cancer at that time.
Drugs: At the present time there are numerous analgesic medications available for dogs with this tumor. No single medication, however, is a match for the pain involved in what amounts to a slowly exploding bone. A combination of medications is needed to be reasonably palliative and should be considered only as a last resort if amputation or radiation therapy will not be pursued. There are several types of drugs that can be combined:
These different drugs are often given together to create meaningful analgesia to the osteosarcoma patient when amputation and radiotherapy are not going to happen.
HOW DO WE TREAT THE CANCER?
Osteosarcoma is unfortunately a fast spreading tumor. By the time the tumor is found in the limb, it is considered to have already spread. Osteosarcoma spreads to the lung in a malignant process called metastasis. Prognosis is substantially worse if the tumor spread is actually visible on chest radiographs, so if chemotherapy is being contemplated, it is important to have chest radiographs taken.
Cisplatin (given IV every 3 to 4 weeks for 3 treatments)
Carboplatin (given by IV every 3 to 4 weeks for 4 treatments)
Doxorubicin (given IV every 2 weeks for 5 treatments)
Doxorubicin and Cisplatin in Combination (both given IV together every 3 weeks for four treatments)
WHAT EXACTLY IS “MEDIAN” SURVIVAL TIME?
When a population is evaluated statistically, there are a number of ways the central tendency of the group can be evaluated. The median is the value at which 50% of the group falls above and 50% of the group falls below. This is a little different from the average of the group, though more people are familiar with this term. When one evaluates median survival times one is looking at a 50% chance of surviving longer than the median (and a 50% chance of surviving less than the median).
WHAT EXACTLY DOES CHEMOTHERAPY PUT MY DOG THROUGH?
Most people have an image of the chemotherapy patient either through experience or the media and this image typically includes lots of weakness, nausea, and hair loss. In fact, the animal experience in chemotherapy is not nearly as dramatic. After the pet has a treatment, one should expect 1 to 2 days of lethargy and nausea. This is often substantially palliated with medications like Zofran® (a strong antinausea drug commonly used in chemotherapy patients). These side effects are worse if a combination of drugs is used but the pet is typically back to normal by the third day after treatment. Effectively, you are trading 8 days of sickness for 6 to 12 months of quality life. Hair loss is not a feature of animal chemotherapy.
While osteosarcoma of the limbs is the classical form of this disease, osteosarcoma can develop anywhere there is bone. "Axial" osteosarcoma is the term for osteosarcoma originating in bones other than limb bones, with the most common affected bones being the jaws (both lower and upper). Victims of the axial form of osteosarcoma tend to be smaller, middle-aged, and females outnumber males two to one.
In the axial skeleton the tumor does not grow rapidly as do the appendicular tumors, thus leading to a more insidious course of disease. The tumor may be there for as long as two years before it is formally diagnosed. An exception is osteosarcoma of the rib, which tends to be more aggressive than other axial osteosarcomas.
Treatment for axial osteosarcoma is similar to that for the appendicular form: surgery followed by chemotherapy. There is one exception, that being osteosarcoma of the lower jaw. Because of the slower growth of the axial tumor and the ability to remove part or all of the jaw bone with little loss of function or cosmetic disfigurement, it has been reported that 71% of cases survived one year or longer with no chemotherapy at all.
For more details on treatment and expectations, we encourage our clients to see a veterinary oncology specialist. Do not consider the Internet as a replacement for the specifics you can receive in a one-on-one consultation with an expert.
IN OUR AREA WE REFER ONCOLOGY CASES TO THE EXPERTS AT THE VETERINARY CANCER REFERRAL GROUP AT THE CITY OF ANGELS VETERINARY COMPLEX:
TO LOCATE A VETERINARY ONCOLOGIST
NO ONCOLOGIST IN YOUR AREA? ON-LINE CONSULTATION AND CHEMOTHERAPY DRUGS ARE AVAILABLE TO ANY VETERINARIAN THROUGH
For more on-line support visit
Page last updated: 9/5/2013