Kristine M. Conner
Last Modified: November 1, 2001
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).
The "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 surgery, 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.
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.
The 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 benefit humans. 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.