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New Treatments for Cancer in Dogs Helps Human Cancer Research

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In the ongoing effort to develop new and more effective treatments for the many cancers that affect humans, medical researchers have traditionally used laboratory mice as experimental subjects. Newly developed chemotherapy drugs are first tested on mice, and those that show promise may be approved for use in clinical trials on small numbers of human patients.

Although this method of testing often produces favorable results, it has its limitations. Mice do not spontaneously develop the same cancers that afflict humans, so researchers must artificially induce the disease in the test animals. Drugs that are effective in treating these cancers in mice are not necessarily effective in treating humans with the same cancers.

Significantly, some of the most common naturally occurring canine cancers – lymphoma, brain cancer, stomach cancer, bladder cancer, breast cancer, and osteosarcoma – are also quite common in humans. Timothy Rocha, DVM, DAVCIM, a veterinary oncologist at NYC Veterinary Specialists, sums up the problem this way: “Lab mice are human creations. Tumors that develop in them are far different from reality. Dogs get real-life tumors.”

For these reasons, researchers have turned to man’s best friend for a better approach to the development of more effective animal models of human cancers. This approach carries the promise of significant new therapies for both dogs and people.

‘Comparative Oncology’: A new approach to cancer research

Like people, dogs and cats develop cancer quite often. According to the Colorado State University Animal Cancer Center, “cancer is the most common natural cause of death in dogs and cats in the United States. Close to 50 percent of dogs and cats will develop cancer if they live ten years or longer.” The American Veterinary Medical Association reports that cancer accounts for nearly half of the deaths in pets more than 10 years of age. Dogs develop the disease at roughly the same rate as humans, while the incidence is lower in cats.The more research that is done with dogs and cats, the better we understand how to care for and treat pets with cancer.

With the dog population in the U.S. now at 65 million, there is an unprecedented opportunity for researchers to study new and innovative treatments in dogs, many of which will likely benefit humans as well.

Recognizing this opportunity, in 2004, the National Cancer Institute – a research arm of the federal government – established The Comparative Oncology Program (COP), a research initiative whose purpose is to use naturally occurring cancer models in dogs as the basis for understanding and developing new treatments for human cancers.

Clinical trials: benefits for both species

In order to advance the development of new cancer drugs, the COP established the Comparative Oncology Trials Consortium (COTC) to conduct clinical trials in pet dogs with cancer. COTC-initiated trials enable pets with cancer to receive new experimental therapies, overseen by board-certified veterinary oncologists at veterinary colleges around the nation. Among the 18 institutions participating in these trials are the University of California-Davis, Colorado State University, the University of Tennessee, the University of Illinois (Urbana-Champaign), Cornell University, and Tufts University.

In a recent interview with WebVet, Melissa Paoloni, DVM, DACVIM, the Deputy Director of the COTC, explained that the program’s methodology is to “use the comparative approach as a model for the study of human cancer.”

Paoloni points to the mapping of the canine genome – which was completed in 2005 – as a critical development that researchers hope will enable them to describe canine cancers with the same degree of sophistication as they do human cancers. 

But developing new drugs that will kill cancer cells – as essential as that is – is only half the battle; getting those drugs to deliver their punch where it’s needed is another challenge altogether. As Paoloni explains, that’s where the field of ‘pharmacodynamics’ comes in. Pharmacodynamics is the study of how drugs react with and affect targets in tumors when actually administered to patients, and is an important component in COP’s research program.

Tangible results I: limb-sparing cancer surgery

Although the comparative oncology approach is relatively new, the use of dogs as a model for human cancer treatment has already shown results.

Using a surgical technique first developed by Stephen J. Withrow, DVM at Colorado State University's Animal Cancer Center for the treatment of dogs with osteosarcoma – a kind of bone cancer that also attacks teenagers – the affected portion of bone is removed and replaced by a bone graft and metal implant. The technique is now commonly used in humans as well. Previously, the only treatment with a promise of cure was amputation of the affected limb.

What made the treatment “translatable” from dogs to humans is the fact that both develop osteosarcoma spontaneously; in fact, it is the most common bone cancer of large and giant breed dogs and shows a very similar pattern of aggressiveness and skeletal location in both species.

Tangible results II: a cancer vaccine

Another exciting development has been the creation of a “therapeutic vaccine” for canine melanoma, an aggressive form of cancer that usually appears in a dog’s mouth, but may also appear in other areas of the body. The prognosis for dogs with this type of cancer is generally poor.

Unlike the kind of vaccines that most people are familiar with – which are used to immunize us against disease – a therapeutic vaccine is used to treat cancer that has already spread beyond its original site by stimulating the body’s own immune system to attack and kill cancer cells. 

The canine melanoma vaccine was developed through a collaboration between Memorial Sloan-Kettering Cancer Center (MSKCC), the Animal Medical Center (AMC) of New York, and Merial, an animal health-care company. As reported by the AMC, an inquiry by Phillip J. Bergman, DVM, to Drs. Alan Houghton and Jedd Wolchok – both of MSKCC – into their research toward a human melanoma vaccine led to parallel clinical trials at the two institutions. Studies at AMC’s Donaldson-Atwood Cancer Clinic have demonstrated “significantly longer life spans even in dogs with advanced stages of melanoma.”

And more advanced treatments do not necessarily mean more time spent in hospitals.  Advancements in both Human and Veterinary medicine allow for people and pets undergoing cancer treatment to spend more time at home, and less time in the hospital.

A new approach brings new hope

Dr. Wolchok sums up the significance of the canine/human cancer connection this way: “Both humans and dogs develop this cancer in exactly the same way. The disease occurs spontaneously through an interaction of genes with the environment. By conducting trials in humans and in animals that live in the same surroundings as humans, there can be a synergy that we hope will result in improved cancer treatment for all.”

Based on the results achieved thus far – and the solid science behind the comparative approach – that hope seems well founded.

 

Credit: Reviewed by Amy Attas, VMD
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