The Importance of Veterinary Oncology
Kristine M. Conner, OncoLink
You may have noticed that OncoLink recently added a
veterinary oncology section to its menu of specialty information. Edited by
Lili Duda, VMD, a radiation oncologist at the Veterinary Hospital of the
University of Pennsylvania, the section is designed as a resource for pet
owners who have an animal diagnosed with cancer or are concerned about that
possibility. The traffic on this area of the site and the response from pet
owners suggest that it is filling a previously unmet need. However, some
OncoLink visitors have expressed concerns about the appropriateness of
including veterinary information on a site that deals primarily with cancer
in humans. This article will explain OncoLink's commitment to veterinary
oncology, drawing on the expertise of Penn's Dr. Duda as well as Stephen
Withrow, DVM, Chief of Clinical Oncology at the College of Veterinary
Medicine and Biomedical Sciences, Colorado State University, who is an
expert on cancer in dogs and co-author of the textbook Small Animal
Clinical Oncology (W.B. Saunders, 1996).
"cancer problem" that many people think of as a human phenomenon also affects
the animals that live among us. Roughly half of U.S. households are home to
companion animals. Like people, more and more companion animals (i.e., dogs and
cats) are living longer due to better
quality of life, preventive medical care, and vaccinations. And longer
life means an increased chance of developing cancer the early 1980s indicated
that nearly half of dogs that lived past age 10 were likely to die of cancer.
Just as most of us can expect to have a personal experience with cancer, whether
it affects our friends, relatives, or even ourselves, many of us are likely to
encounter this disease through our pets as well.
While veterinarians have been treating and studying
cancer for some time, it was just a decade ago that veterinary oncology was
approved as a board-certified discipline under the American College of
Veterinary Internal Medicine. In 1994, radiation oncology was approved as a
specialty. At least in part, this was a response to the increasing
prevalence of cancer in animals and pet owners' desire for treatment options
besides euthanasia (putting the animal to sleep). The three standard
treatments for cancer in humans —
radiation therapy, and
chemotherapy — have been adapted successfully to help animals with
cancer. While the goal in treating people is to cure the cancer, treatment
for animals focuses on alleviating pain and suffering and extending life, as
long as the quality of that life can be preserved. Dr. Lili Duda puts it
this way: "We're not willing to undertake an aggressive treatment that might
cure half of our patients if it is very likely that it will make the other
half suffer from serious and even fatal complications." Therefore, treatment
is typically much less aggressive than in humans, where the usual goal is
curing the cancer.
Treatment goals may differ, but
cancer in companion animals and humans is essentially the same disease. Both Dr.
Duda and Dr. Stephen Withrow point out that "cancer is cancer," regardless of
whether it develops in a person, dog, or cat. Dr. Withrow notes that roughly 80%
of animal cancers — breast, brain, and bone especially — are a "direct
correlate" to human cancers, and he spends as much of his time delivering
lectures at medical meetings devoted to human topics as at those that are
veterinary-related. Thus, any work that extends our knowledge about cancer,
whether focused on humans or animals, is extremely important.
Veterinary oncology deserves our attention, primarily for the following
To their owners, companion
animals are real family members.
Numerous studies have shown that the emotional bond between human and animal
is just as real as the bond between humans. Dr. Lili Duda points out that, for
many people, pets are "surrogate family members," and even more so for those who
are widowed or live away from family and friends -- an increasingly common
phenomenon in today's mobile society. The mental anguish and anxiety experienced
by owners of pets with cancer are an undeniable part of cancer's impact on
people. A cancer diagnosis is traumatic, but it is less traumatic if the owner
can be given options besides euthanasia. Veterinary oncologists offer pet owners
the chance to alleviate any pain or suffering while extending the animal's life
or even saving it. While not every pet owner can or will choose to treat an
animal's cancer, having that choice is important. As in the case of human
cancers, education and choices are empowering.
study and treatment of cancer in animals takes no resources away from the study
and treatment of cancer in people.
Veterinary cancer treatment and research programs are usually housed in
schools of veterinary medicine and veterinary hospitals affiliated with
universities, separate from human cancer programs. Furthermore, people use their
own discretionary income to pay for the treatment of cancer in animals animals —
money that might otherwise go toward a vacation, home improvement, savings, or
other leisure activity. As Dr. Duda points out, this is not money that would
otherwise go to research on or treatment of human cancers.
When veterinary cancer researchers receive funding
from an organization like the National Institutes of Health, as Dr. Stephen
Withrow and his colleagues at Colorado State University do, it is often because
their research has direct applicability in better understanding or treating
cancer in people. Some clinical trials that involve cats and dogs with cancer
are not only meant to benefit the animals, either by giving them access to a
promising new treatment or learning something new that can help other animals,
but also help people with cancer. These trials produce data and other
information that may then be used to shape the design of trials that enroll
people. Pet owners often are asked to cover just a part of the cost of the
animal's participation. Thus, their money may be facilitating new discoveries
that eventually will be applied to human cancers. In this way, resources devoted
to the study and treatment of cancer in animals may actually contribute
to the study and treatment of cancer in people.
"At worst, it's neutral," stresses Dr. Duda, meaning
that veterinary oncology takes nothing way from human oncology. "At best, it not
only provides a societal service but is also a potential source of information
that can help people with cancer."
Studying cancer in companion animals has and will continue to shed
important light on cancer in humans.
As Lili Duda points out, for a long time the prevailing model has been for
new anti-cancer agents to be tested in laboratory rats or mice first.
Researchers artificially induce cancer in these lab animals or transplant it
into them. If the agent shows promise in the lab, it can progress to
clinical studies involving people. Often, though, the treatment does not
produce the same promising results, possibly because rodents are so
different from humans, or maybe because the cancer was induced and did not
occur spontaneously or naturally. Says Dr. Withrow, "It's a far cry from
what happens in nature."
Cats and dogs with cancer
provide a better model for what happens in people, both because their cancer
occurs spontaneously, and they are more similar to humans physiologically.
"These cancers better mimic what happens in people," says Dr. Duda. "Pets live
in our homes and share our environment humans. Dr. Duda says that she and other
veterinary oncologists would like to see this model turned around, with the most
promising new treatment approaches being used in companion animals first. Of
course, these clinical trials must be designed to ensure that the animal is not
subjected to any unnecessary risks or pain, just as human clinical trials are.
But well-designed studies of treatments in companion animals stand to benefit
both pets and their owners and
possibly people with cancer.
Dr. Withrow's work on
osteosarcoma in dogs is one of the best examples of how veterinary oncology can
Osteosarcoma is a type of bone cancer that is extremely common in dogs.
While relatively rare in people, it does affect roughly 1,000 to 1,500 young
adults between the ages of 10 and 20 each year. The cancerous lesions usually
are located in the knee region, but they can be found in any bone. At one time,
the standard treatment was amputation of the limb techniques for resecting the
tumor and reconstructing the limb, amputation is no longer the only option. Dr.
Withrow and his colleagues contributed to the improvements in treating
osteosarcoma by conducting clinical trials with dogs, in which they evaluated
different ways of using surgery in conjunction with chemotherapy to treat the
disease. They also evaluated different surgical techniques for removing the
tumors and rebuilding the
limb. "Dogs are a tremendous model for human osteosarcoma," Dr. Withrow
says. "The histology is the same, it spreads the same way, and it responds to
chemotherapy like it does in people." Treating these tumors in larger dogs, he
adds, parallels their treatment in young adults, which is why their results are
useful to physicians. Furthermore, while he is likely to see about 150 cases of
osteosarcoma in a year, a physician would be more likely to see one or two at
most. Thus, a veterinarian is in a better position to study the disease from all
angles than a physician would be. The same goes for non-Hodgkin's lymphoma, he
says, which is also much more common in dogs than in people.
Companion animals are a useful model for another reason: time. Cancer progresses
much more quickly in animals than it does in humans, and therefore clinical
trial data is available much faster. For instance, notes Dr. Withrow, it only
takes eight to nine months for breast cancer to spread in dogs, versus roughly
five years in women. "You might have to follow a child for 20 years after a
trial to see if the cancer recurs," says Dr. Lili Duda, "but you would know this
within a few years with an animal." Thus, veterinary oncologists know sooner if
the cancer is going to spread or recur, and how long the animal can survive. In
this way, animals with cancer are a potential source of relatively quick data
that may help shape human cancer research.
Coordinating research on companion animal cancers with human cancer
research, often called "parallel research" or "comparative oncology," is a
relatively new direction. However, it holds forth great promise. For
example, cancers of the mouth and throat, which are routinely treated in
veterinary hospitals, may help us better understand human oral cancer.
Photodynamic therapy, which involves using a drug to make a tumor sensitive
to light and then exposing it to laser light, is now being evaluated in
animals (as well as in human clinical trials). It is being used to treat
skin cancers in cats at the University of California, Davis, Center for
Companion Animal Health, as well as prostate cancer in dogs at the
University of Pennsylvania. Perhaps these studies will build on our
understanding of how this therapy can help people.
Other veterinary oncologists are investigating how pets may serve as
"sentinels" for the changing patterns of cancer development in humans. Since
dogs and cats share our environment, they may help us to pinpoint some of
the factors that may be contributing to cancer rates.
Thus, veterinary oncology is helping pets with cancer to
live better, more comfortable lives, while also seeking to advance treatment
methods. Pet owners have more options than they ever did before. And if
money is an issue, they may be able to gain access to treatment through a
clinical trial. The trial's sponsoring organization usually covers part or
all of the treatment cost. Furthermore, veterinarians' work is producing a
body of new information about cancer that stands to benefit all of us —
human and animal.
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