Issue Description Osteosarcoma is the most common primary bone
tumor in dogs and cats. Approximately 80-85% of all canine skeletal
tumors are diagnosed as osteosarcomas. Other Names Osteosarcoma, Canine Osteosarcoma
Risk Factors Osteosarcoma is the most common bone tumor in
dogs and typically afflicts middle-age large and giant breed dogs such
as Irish Wolfhounds, Greyhounds, German Shepherds, Rottweilers,
Doberman Pinschers and Great Danes. It has a ten times greater
incidence in dogs than humans. A hereditary base has been shown in St.
Bernard dogs. Spayed/neutered dogs have twice the risk of intact ones
to develop osteosarcoma. Infestation with the parasite Spirocerca lupi
can cause osteosarcoma of the esophagus.
Symptoms 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 1-3 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.
Diagnosis One of the first steps in evaluating a
persistent lameness is 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" - looks like an area of bone has been eaten
The "sunburst" pattern - 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.
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
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.
Treatment 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.
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"
Complications of limb sparing can include: Bone infection, implant
failure, tumor recurrence, and fracture.
Prognosis 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