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TREATMENT OF OSTEOSARCOMA INVOLVES TWO ASPECTS:TREATING THE PAIN CAUSED BY THE BONE TUMORAND FIGHTING THE SPREAD OF THE CANCER.
HOW DO WE TREAT THE PAIN?
Keep in mind that dogs are usually euthanized due 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.
While losing a leg is very handicapping to a human (who only has two legs total), losing one leg out of four does not restrict a dog’s activity level. Running and playing are not inhibited by amputation (after the surgical recovery period is over).
While losing a limb is disfiguring to a human and has social ramifications, dogs really are not so self-conscious about their image. The dog will not feel disfigured by the surgery; it is his or her owner that will need to adjust to the new appearance of the dog.
Median survival time for dogs who do not receive chemotherapy for osteosarcoma is 4-5 months from the time of diagnosis regardless of whether or not they have amputation. Do you want your dog’s last 4-5 months to be painful or comfortable?
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 (ie fixed in one position and cannot be flexed or extended.)
Limb sparing cannot be done if more than 50% of the bone is involved by tumor or if neighboring muscle is involved.
Limb sparing does not work well for hind legs or tumors of the humerus (“arm” bone.)
Limb sparing works best for tumors of the distal radius (“forearm” bone).
Complications of limb sparing can include: Bone infection, implant failure, tumor recurrence, and fracture.
RADIOTHERAPY FOR PAIN CONTROL : Radiation doses can be applied to the tumor in 3 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 0-19 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. In the Los Angeles area, a course of 3 doses of radiotherapy typically costs $700-$800.)
When pain is relieved in the tumorous limb, there is an increase in activity which can in turn lead to a pathologic fracture of the bone.
Radiotherapy does not produce a helpful response in about 1/3 of patients. (Remember, amputation controls pain in 100% of cases but if amputation is simply not an option, there is a 2 out of 3 chance that radiotherapy will control the pain.)
DRUGS: Analgesic medications such as carprofen, etodolac, aspirin, butorphanol, and fentanyl patches are all available but, unfortunately, they are no match for the pain involved in what amounts to a slowly exploding bone. These medications may be palliative at some stage but generally do not provide meaningful pain relief long term.
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 radiographs in the chest so if chemotherapy is being contemplated, it is important to have chest radiographs taken.
Chemotherapy is the only meaningful way to alter the course of this cancer.
Young dogs with osteosarcoma tend to have shorter survival times and more aggressive disease than older dogs with osteosarcoma.
Elevations of "Alkaline phosphatase," one of the enzymes screened on a basic blood panel, bode poorly. These dogs have approximately 50% of the survival times quoteed below for each protocol.
CISPLATIN (given IV every 3-4 weeks for 3 treatments)
The median survival time with this therapy is 400 days.
Survival at one year: 30-60% (depending on what??)
Survival at two years: 7-21%
Giving less than 3 doses does not increase survival time (ie if one can only afford one or two treatments, it is not worth the expense of therapy)
Cisplatin can be toxic to the kidneys and should not be used in animals with pre-existing kidney disease.
CARBOPLATIN (given IV every 3-4 weeks for 4 treatments)
Similar statistics to cisplatin but carboplatin is not toxic to the kidneys and can be used if the patient has pre-existing kidney disease.
Carboplatin is substantially more expensive than cisplatin.
DOXORUBICIN (given IV every 2 weeks for 5 treatments)
The median survival time is 365 days.
10% still alive at two years.
Toxic to the heart. An ultrasound examination is needed prior to using this drug as it should not be given to patients with reduced heart contracting ability.)
DOXORUBICIN AND CISPLATIN IN COMBINATION (both given IV together every 3 weeks for 4 treatments)
48% survival at one year
30% survival at two years
16% survival at three years.
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 1-2 days of lethargy and nausea. This is often substantially palliated with medications like Zofran® (a strong antinauseal 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 6-12 months of quality life. Hair loss is not a feature of animal chemotherapy.