Free Zoobiquity by Barbara Natterson-Horowitz Page B

chemicals, infections, and medications during their tours of duty. §
    Where we don’t overlap might be telling, too. Dogs rarely get colon cancer. Lung cancer is also atypical, although short- and medium-nosed dogs living in homes with smokers are susceptible. Canine breast cancer is rare in countries that promote spaying but quite common where most female dogs remain reproductively intact. In humans, too, oophorectomy (removal of the ovaries) and premature ovarian failure dramatically reduce breast cancer risk.
    But beyond their possible use as canine canaries in our domestic coal mines, dogs may be ideal proxies for studying the actual biology of how cancer works in our own bodies.Currently, the vast majority of cancer studies are done on mice. So-called humanized mice have been specially bred to mimic our gene patterns. Often their immune systems have been altered to allow the cancer to grow. Most lab mice are “given” cancer; usually it doesn’t arise spontaneously in their bodies. For decades, this “artificial” cancer has yielded useful insights into tumor biology—how cells divide, how tumors form, how they metastasize and spread to other parts of the body. But the genesis of the disease, its complexity, how it becomes resistant to therapy, and how it recurs are really not answerable in mouse models. Even side by side, under a microscope, mouse tumors are very different from human tumors.
    Our human tumors, it turns out, are remarkably similar to those of the animals with whom we live: our pet dogs.Dog cancer cells and human cancer cells are nearly indistinguishable. Dogs live longer than mice, so researchers can observe the cancer—and the treatments—over the long term. And, unlike most lab mice, pet dogs’ immune systems are intact, allowing oncologists to study how a cancer acts when challengedby natural defenses. Dogs are also simply much bigger than mice. This has implications, both practical—the tumors are physically easier to see—and philosophical (think of Peto’s paradox).
    Here I must pause to make absolutely clear that I’m
not
talking about experimenting on dogs in labs. I’m talking about the opposite. Observing cancer while caring for companion animals—pets—who develop cancer spontaneously and receive treatment from veterinarians.
    This novel approach is known as comparative oncology. Recognizing that studying naturally occurring cancers in the animals that share our homes might unlock some of cancer’s mysteries, the National Cancer Institute launched the Comparative Oncology Program (COP) in 2004. One of the COP’s early innovations was to pool the brain trusts of twenty top-tier veterinary teaching hospitals in the United States and Canada. This network, called the Comparative Oncology Trials Consortium, conducts clinical trials in pet dogs, searching for new anticancer drugs and treatments for human patients. (The trials are sponsored by pharmaceutical companies hoping to bring new human therapies to market.) But while pet health may not be the intended goal of the program, some of the advances that benefit humans will come back full circle to enhance the health of animals, too.
    Comparative oncology has already improved the health of many animals, including us. It’s not a stretch to say that new cures have come out of cross-species cancer comparisons (although physicians and veterinarians alike tend to manage expectations with more clinical terms like “novel therapeutic strategies” and “positive survival rates”).For example, the limb-sparing technique that human doctors use today to save teenagers with osteosarcoma from amputations was pioneered in dogs by a veterinary oncologist, Stephen Withrow, and his team at Colorado State University, working jointly with physicians. And a potential cure for malignant lymphoma using transplanted stem cells was first successful in twelve pet dogs under treatment at Fred Hutchinson Cancer Research Center in Seattle, paving the