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Advancing cancer treatment
A Q&A with small-animal oncologist specialist Dr. Stephen Withrow


DVM: You're the only veterinarian who's been admitted as a member to the Musculoskeletal Tumor Society. What are the advantages to joining a human medicine association?

Withrow: About 20 years ago, I was doing a sabbatical at Massachusetts General Hospital in Boston where they really embraced the idea that animal studies, when conducted humanely, can be beneficial to human medicine. At the time there were fewer than 100 people worldwide conducting concerted osteosarcoma research in humans.

I was doing a fellowship with Dr. Henry Mankin, and he was a member of the society. I attended a meeting as a guest. Henry nominated me for membership, and the group voted me in as the sole veterinarian in the group. From the society, I met Dr. Ross Wilkins, a Mayo Clinic-trained researcher who was doing very similar work with osteosarcoma in people as I was doing with animals. And he was based here in Colorado. We began a long friendship, and, through the years, we've collaborated on a lot of work. Through the society, I met the players in the field of sarcoma research and got access to intellects and ideas. And I was their check and balance with ideas relating to animals and pet animal studies. So it's been beneficial both ways.

DVM: The Animal Cancer Center (ACC) is the largest such facility in the world, and it's received 25 consecutive years of funding by the National Cancer Institute. Can you tell us about the center?

Withrow: When I came to Colorado State in 1978, I had an interest in cancer, but there was not much work being done in the field. At first I was doing orthopedics and neurosurgery. Eventually, I met Dr. Ed Gillette, a radiation researcher, and we built a partnership with me as the clinician. We were able to get the center started with some multiple and diverse funding sources. In time, I devoted myself exclusively to cancer.

The Animal Cancer Center grew into a full-service cancer treatment center, offering chemotherapy, radiation, surgery and clinical trials. By 2002, it had grown, and we moved into a 35,000-square-foot cancer research facility. Today, we have teaching facilities; we offer clinical services; and we conduct research and public outreach. We do about 3,000 consultations worldwide annually. And we have 10 labs and employ about 100 people. It's a small business with a diverse funding base. Our core areas of research include pharmacology, nutrition, immunology, genetics, imaging, trials, pathology, physics and musculoskeletal biology.

DVM: Are most of your clients from your area?

Withrow: Yes, about 75 percent of our patients are from Colorado, and about 25 percent of our patients come from all over the world. We see about 5,000 oncology appointments annually.

DVM: How prevalent is cancer in the pet population? Is that number growing or declining? Are certain breeds at risk?

Withrow: We make educated guesses about pet cancer numbers. In human medicine, cancer is a reportable disease, so researchers can get real numbers on incidence, location, type of cancer and that sort of thing. But we don't have that registration requirement yet in veterinary medicine.

The general numbers are these: one in two men, one in three women, one in four dogs and one in five cats will develop cancer at some point in their lives. That said, there are some breeds of animals in which we expect up to 50 percent to contract cancer. It's a moving target, with one of the highest-risk breeds being golden retrievers. We see more cancer in purebred dogs, but we're unsure if the causes are genetic, environmental or nutritional. There also seems to be a higher prevalence of cancer in breeds such as greyhounds, Bernese mountain dogs and flat-coated retrievers.

DVM: Are certain types of cancer more common now than in the past?

Withrow: We're not seeing an epidemic of any individual cancer. That said, we're seeing more vaccine-associated sarcomas in cats, but we're unsure if they're newly developed or they're just newly recognized. We've been able to make some recommendations for cats that get vaccinated regularly, such as using an alternate site or adjusting the timing of the vaccination. And in those cases, the incidence of feline vaccine-associated sarcomas has declined.

For a while, thyroid cancer in cats was seemingly epidemic, but in recent years, those numbers have fallen off. We're still unsure of what triggered the spike. Was it environmental? We don't know. We need more research on that. It's interesting to note that bone cancer is almost identical in dogs and people, but it's practically benign in cats. Certain mouth cancers are curable in dogs and humans, but not in cats.

DVM: What are the most difficult types of cancer for veterinarians to treat and why?

Withrow: Advanced and invasive local disease is hard to treat. These are cases when the pet owner didn't bring the animal in soon enough, or the veterinarian didn't recognize the lump as a problem and by the time we get them, the tumors are big and potentially bad. In addition, cancers we detect late and have spread beyond the initial site are always hard to treat.

DVM: When should a veterinarian recommend surgery for cancer patients?

Withrow: My challenge as a surgeon is to figure out how to stop the tumor growth at the initial site. This is often a formidable challenge. But we've found, as in human medicine, that individualized, customized treatments tend to work best. For example, while surgery is the cornerstone of veterinary oncology, we're also seeing more use of radiation, which is now limited only by the lack of training programs and equipment. Chemotherapy is gaining in popularity and accessibility and is limited only by the cost and potential for toxicity.

Then there are more experimental therapeutics available for clients to purchase and clinical trials that pet owners can enroll their pets in. This is a promising field. Currently, we have 22 clinical trials going at ACC, and two or three show real promise. Of course, it generally takes us one to two years to complete each one, and the trials themselves are not cheap.


Source: DVM360 MAGAZINE,
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