Exploring pet cancer with veterinary oncologist Stephen J. Withrow

Cancer in companion animals remains one of the biggest concerns of pet owners, but veterinary oncologists are making important strides in research, diagnostics and treatment choices.

Stephen J. Withrow, DVM, Dipl. ACVS, Dipl. ACVIM, director of the Animal Cancer Center at Colorado State University, is a leading expert in cancer research, whose work appears in numerous texts and scientific papers.

Withrow, who earned his DVM degree at the University of Minnesota, joined the faculty of the College of Veterinary Medicine and Biomedical Sciences at Colorado State in 1978 and was honored as Distinguished Professor in 2004.

He developed a limb-sparing technique to treat osteosarcoma in dogs, one that often is used at human cancer centers, especially for children.

Withrow recently answered some questions on cancer issues in a discussion with DVM Newsmagazine.

DVM: What are some of the most insidious cancers in pets?

Withrow: Skin tumors and other cancers on the outside of a patient are easy. Internal cancers — of the brain, spine, chest cavity, lung, spleen, liver — are the ones that are the foolers or that originate in the blood in places you can't see. Those would be the most insidious.

Public awareness and veterinarian awareness have increased the number of diagnoses of cancers in pets, but that doesn't mean there is an epidemic of cancer. The incidence has not increased. Instead, the number of diagnosed cases has increased. That's more about surveillance on the part of veterinarians and clients.

Cancer is not contagious in 99 percent of cases. Unfortunately, there's this public perception that cancer is running rampant in pets. Again, public awareness, veterinarian awareness and surveillance all contribute to the increased number of diagnoses.

DVM: How is the human-animal bond intensified (or not) in cancer patients and their owners? What are some ways DVMs can address this?

Withrow: Animals have become more critical as part of family units. Today there are more latchkey kids and single parents. And, people are living longer. Once the kids leave the house, what do you have? A dog or a cat. In pets with cancer, where they suffer some consequence of the disease, it gets personalized because of the prevalence of cancer in humans.

DVMs can continue to maintain awareness by understanding the warning signs of cancer published through the Veterinary Cancer Society. Lumps or bumps that continue to grow, weight loss, not eating, vomiting, diarrhea are all signs of potential cancer cases. There needs to be an awareness that cancer should be in the differential diagnosis.

DVM: Do you have any diagnostic tips for identifying cancers early?

Withrow: Awareness is important. A fine needle aspirate for level of suspicion is one method. Understand that a lump is not just a lump. In modern days, we're seeing a tremendous increase in imaging, CTs and MRIs. These tools have really expanded our diagnostic armamentarium. It's important to consider that cancer may be a possibility and to approach from the mindset of wanting to rule it out instead of ignoring it.

DVM: Are there any myths related to pets with cancer that you'd like to bust?

Withrow: People need to understand that cancer is controllable, and sometimes it is even a curable disease. However, you don't have to cure to heal. There's always something that can be done to improve quality of life.

Cure rates for malignant tumors in pets are 25 percent to 30 percent. In human medicine, it's 40 percent to 50 percent for adults and 70 percent to 80 percent for children.

We can provide quality of life at the very least if we're unable to cure the pet. In many ways, with treatment of cancer, there are almost too many choices. Know that doing nothing is also a valid choice as long as you are accurately informed of your choices.

DVM: What are some trends in cancer research?

Withrow: One trend is to individualize and customize treatment to the patient and their specific disease. Today, we have surgery by dose, radiation by dose, chemotherapy by dose. The real trend is individualizing patient care.

We're also identifying specific nontoxic targets. Instead of the same chemotherapy with a marginal result, we're moving toward molecularly driven, targeted and possibly individualized therapy.

On the human therapeutic treatment side, Gleevac is a huge molecularly target-based breakthrough. It gives us hope that we can do targeted therapies.

DVM: How about innovative therapies?

Withrow: There are new targeted therapies with mast cell cancer. One comes from Pfizer. These are different approaches to the disease. It gives us hope that if we understand the tumor cell better and understand the Achilles heel of how the tumor cell can be attacked, we can kill the tumor but not the patient. That is therapeutic gain. We have to be sure to balance side effects of treatment vs. benefit. That's where you walk a tightrope.

Cancer often is portrayed as one disease, but in fact it is comprised of hundreds of diseases that respond differently whether you're a dog or cat, a small dog or a larger dog, whether it's in the head or toe and so forth. That's why customized medicine has a different approach. One goal remains to find it early. Early detections go a long way toward potential cure.

DVM: Has the lifespan improved for cancer patients?

Withrow: Yes. I'm old enough to remember the test and slaughter days. If they said it was cancer, the pet would be euthanized. In today's world, it's a far different story with our modern referral centers, advanced radiation, surgical and chemotherapy options. Cure rates 30 years ago were around 10 percent; now they are 30 percent or better.

DVM: What's it like to run the largest animal cancer facility in the world?

Withrow: Every day is inspirational. I'm privileged to work with good people with inquisitive minds. Daily I get to see how research impacts our lives. The teaching, service and research are all intertwined.

DVM: I read where the National Cancer Institute funds you. Do they fund specific research? Is this unusual in the veterinary profession?

Withrow: We've received 25 consecutive years of funding from the NCI. One of the new initiatives funded by them is the Clinical Oncology Trials Consortium. This is comprised of 18 veterinary schools that banded together to do clinical trials on agents likely to impact human and pet animal disease. NCI's endpoint is human-related. Ours is both for critters and people. That's one initiative funded by them with immediate translational impact.

Another funded initiative is the Pfizer-sponsored Comparative Canine Oncology and Genomics Consortia. This is a tissue-archiving tumor bank that has eight schools participating. Participants send tumor tissue to Bethesda, Md., that is going to populate a bank of 3,000 tumor samples. The goal is to have melanoma, bone marrow, etc., ready to study. This is a national archive, but we also run our own tissue bank intramurally. These are very exciting initiatives.

With NCI, to maintain the funding, you have to show progress, that it's translational and that you're producing results.

Here at our center, we are also working on a trial with the COTC that is targeted for osteosarcoma cancer. It is jointly funded by the Morris Animal Foundation and approved and endorsed by a Childrens' Oncology Group. Specifically, it's a study of an agent called rapamycin. It's the story of an old drug taking on a new life.

DVM: What take-home message would you like to share with fellow DVMs when faced with cancer patients?

Withrow: That cancer is treatable. And it's more curable than commonly treated diseases like diabetes and heart failure. Part of this is perception: Some owners and veterinarians think cancer is a death sentence. There is hope for treating cancer and providing good quality of life. It's also important to note that we're getting better at treating it. I'm 61, and I've seen many positive changes over my oncology career. It was barely diagnosed and barely treated when I started. There have been huge strides since then.

Skernivitz is a Cleveland free-lance writer.