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Pet Article
PETS AND BONE CANCER
Medical research carried out at the University of Illinois College of Veterinary Medicine at
Urbana may one day benefit you as well as your pet. Dr. Nicole Ehrhart, veterinarian and
surgical oncology specialist at the Veterinary Medicine Teaching Hospital, is studying bone
growth and repair in dogs receiving chemotherapy. Her research is finding new alternatives
to amputation and intravenous (IV) chemotherapy and improving the accuracy of prognosis
following the treatment of bone cancer.
When dogs get bone cancer in a limb, the traditional treatment is amputation and
chemotherapy. Alternatively, the limb can be saved with a "limb-sparing" technique by
transplanting donor bone from a cadaver. A new form of limb-sparing, known as bone
transport, grows new bone in the gap left after bone tumor removal.
With the bone transport technique, a cross-sectional piece of the remaining normal bone is
cut and moved a short distance from the area it was removed from. The body recognizes
this as a fracture and begins to heal it. A device called an Ilizarov, named after the Russian
scientist who developed it, holds the cut piece of normal bone in place and allows it to be
moved a short distance each day. As the cut piece is moved further and further away from
its original site, new bone grows behind it.
The advantage of bone transport over the use of a donor bone is that the patient's own
bone is growing. Cadaver bone is both expensive and susceptible to infection. Until the
body establishes a blood supply to it, the new bone is a high-risk environment for bacterial
infection. About 35 percent of these patients get infections. Bone transport patients always
have a blood supply to the growing bone, which allows the immune system to take care of
any infection.
"This method has been used successfully in people with bone loss from trauma, such as
motorcycle accidents. It has never been done with chemotherapy. Bone cancer has to be
treated with chemotherapy. Nobody knows the effect of chemotherapy on bone that grows
as you transport the bone," says Dr. Ehrhart. "We are researching this limb-sparing option
for dogs, but it may also benefit humans. Bone cancer affects children more often than
adults, and children are still growing. This technique would allow new bone in kids to grow
out to equal length as the opposite limb."
If it turns out that chemotherapy hinders new bone growth, Dr Ehrhart's research should be
able to find out why. By comparing groups of control dogs and chemotherapy dogs, she
hopes to isolate proteins responsible for bone growth. The next phase will be to give these
proteins to the chemotherapy group to see if it stimulates bone growth.
"We are also studying an alternative to IV chemotherapy," says Dr. Ehrhart. "We are one of
only two institutions with USDA permission for clinical use of a biodegradable polymer
sponge that dissolves over time when implanted in the body, providing a slow-release
chemotherapy." In preliminary trials this method has been shown to work as well as IV
chemotherapy. The slow-release chemotherapy has the potential to control local recurrence
of the tumor as well as metastatic disease (spread of the tumor). This method of
chemotherapy is less toxic than IV chemotherapy and requires fewer doses. Clinical studies
will begin here this fall on dogs with cancer.
"Another study we are doing will enable us to make more accurate prognoses for animals
with bone cancer," Dr. Ehrhart says. "There is evidence that the amount of bone-specific
alkaline phosphatase in the blood before and after cancer surgery is a good indicator of
post-surgical survival time." Patients with higher than normal levels of this enzyme in their
blood before they have surgery have a poorer prognosis than patients with lower levels.
Also, if the amount of this enzyme in the blood does not return to normal after surgery, then
the patient has a lower chance of survival and a lower remission-free interval than normal.
This finding is independent of the stage, the location, and the amount of cancer present and
of metastatic disease, but it is correlated with survival time. This information will provide a
more accurate prognosis than before. Patients with higher bone-specific alkaline
phosphatase levels can be treated more aggressively with chemotherapy after surgery in
order to achieve the same survival rates as patients with lower levels.
"Animal research and human research are very intertwined," says Dr. Ehrhart. "Usually
disease is induced in animals to provide research models for human medicine. Our research
is with naturally occurring bone tumor patients. We work to improve the animal's quality of
life, and the information we get is helping to improve the quality of life of people with bone
cancer, too.
Mark Woodcock
1 Flea Control
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