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Canine Osteosarcoma
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THE PET HEALTH
LIBRARY
Osteosarcoma
(Canine)
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.
Osteosarcoma can develop in any bone but the limbs are the most
common areas affected.
Osteosarcoma develops deep within the bone and becomes progressively
more painful as it grows outward and the bone is destroyed from the
inside out. The lameness goes from intermittent to constant over 1 to
3 months. Obvious swelling becomes evident as the tumor grows and normal
bone is replaced by tumorous bone.
Tumorous 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 may be the finding that confirms the diagnosis of bone tumor. Pathologic
fractures will not heal and there is no point in putting on casts or
attempting surgical stabilization.
How Do we Know my Dog Really Has an Osteosarcoma?
Radiographs: One of the first steps in evaluating a persistent
lameness is radiography (x-rays). Bone tumors are tender so it is usually
clear what part of the limb should be radiographed. The osteosarcoma is
creates some characteristic findings:
The lytic lesion - it looks like an area of bone has been eaten
away.
The sunburst pattern - it shows as a corona effect as the tumor
grows outward and pushes the more normal outer bone up and away.
A pathologic fracture may be seen through the abnormal bone.
Osteosarcoma does not cross the joint space to affect other bones
comprising the joint.
In most cases, radiography is all that is needed to make the diagnosis
but sometimes there are ambiguities.
Biopsy: A tiny section of bone can be removed for laboratory
analysis. This type of analysis is considered to be absolute proof of
diagnosis.
The procedure is associated with some pain and our local oncologists
have suggested that biopsy is not needed if the radiographs show an
obvious bone tumor. If there is any question about the lesion on the
radiographs, a bone biopsy should provide clear results.
Sometimes a bone tumor is surrounded by an area of bone inflammation
and it may be difficult to get a diagnostic sample and several samples
must be taken. These samples are too small to cause a pathologic fracture.
Amputation of the affected bone is recommended for any tumor involving
bone. When the malignant structure has been removed, it is submitted
for biopsy and the diagnosis confirmed at that time. Biopsy before amputation
is felt to simply add a painful procedure to the patient and, if possible,
is reserved for tissue already amputated.
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 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: Coccidioides 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 coccidioidomycosis.)
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 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: Treating the pain
caused by the bone tumor and fighting the spread of cancer.
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.
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 to 5 months from the time of diagnosis regardless of
whether or not they have amputation. Do you want your dog's last 4 to 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 (i.e., 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 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.
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 chest radiographs, 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 quoted below for each protocol.
The presence of tumor in lymph nodes local to the leg being amputated
also bodes poorly. In the study by Hillers et. al published in the April
15th, 2005 issue of the Journal of the AVMA, median survival was significantly
longer (318 days vs. 59 days) in dogs where the tumor was not evident
in local lymph nodes at the time of amputation.
Cisplatin (given IV every 3 to 4 weeks for 3 treatments)
The median survival time with this therapy is 400 days.
Survival at 1 year: 30% to 60%
Survival at 2 years: 7% to 21%
Giving less than 3 doses does not increase survival time (i.e.,
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 by IV every 3 to 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 2 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 four treatments)
48% survival at 1 year
30% survival at 2 years
16% survival at 3 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 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.
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. Your veterinarian can refer you to
an oncology specialist or do your own search at www.vetquest.com.
Date
Published: 3/29/2002
Copyright
2002 - 2007 by the Veterinary Information Network, Inc. All rights reserved.
This work was originally published by Veterinary
Information Network, Inc. (VIN)
and is republished with VIN's permission.
Join
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Bonecancerdogs
List
A Yahoo list group for owners of dogs with bone cancer, a great
source for information and support
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.
