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Aging Lessons

Dogs get the same cancers as humans: prostate, lung, breast/mammary, head and neck, soft tissue sarcomas, melanoma and the bone cancer osteosarcoma, making them a good model for cancer studies in people. The treatment options are also similar: surgery, chemotherapy and radiation. Statistics compiled by the National Cancer Institute, the American Veterinary Medical Association and the American Cancer Society are dramatic: Each year, some 6 million of the 65 million dogs in the U.S. will be diagnosed with cancer. Cancer is the major lifespan glitch, causing nearly half the deaths of dogs age 10 years and over. There are also more than 11 million Americans living with cancer, and over one million new diagnoses each year.

 

Canines offer a unique opportunity to explore the gene-environment interactions that lead to the disease. Because dogs share many of the same environments and living conditions as humans, veterinary pathologists at Tufts’ Cummings School of Veterinary Medicine are studying how commonly used environmental chemicals may cause cancer in dogs.

 

Comparative oncology—studying animals with cancer in the context of how people get the disease and respond to treatment—is an emerging field, and one that has caught on with vets, medical oncologists and universities involved in cancer research. At Tufts, vets are collaborating with oncologists at Massachusetts General Hospital to gain insights into osteosarcoma, the most common bone malignancy in humans. According to Dr. Lisa G. Barber, a veterinary oncologist at the Cummings School, limbsparing surgeries used to treat children with cancer were first developed in dogs.

 

Comparative oncologists are working on three fronts: understanding environmental risk factors such as exposure to pesticides and tobacco smoke, unraveling cancer’s genetic footprints and finding new treatments. Other efforts include the Animal Cancer Foundation’s (acfoundation.org) focus on furthering research in this field, the National Canine Cancer Foundation’s (wearethecure.org) creation of a detailed library of every cancer known to affect dogs and the mapping of the canine genome, which was funded by the National Institutes of Health.

 

Gene mapping will also help Purdue researchers unwrap the treasures of the Old Grey Muzzle Tour—the stuff that makes a Rott a Rott, and an old Rott a longevity scientist’s workhorse. The breed is prone to a particularly aggressive form of cancer, and Waters’ team thinks they may know why. Though it goes against everything vets have been advising for years, recent research conducted by Waters and others indicates that delaying sterilization may increase a dog’s lifespan. Needless to say, the work is controversial. 

 

Study of the non-reproductive effects of sex hormones is in its infancy, but Waters’ work adds to the uncertainty felt by vets who are beginning to question what to tell clients about “fixing” their dogs. For one thing, there’s a higher incidence of testicular and mammary cancer in intact animals. But testicular cancer responds to castration, while castrated dogs have up to a four times greater risk of developing prostate cancer. Sterilized dogs also have a 1.5 to 3 times greater chance of developing bladder cancer.

 

In his blog post, “Spaying, Neutering and Cancer in Rottweilers,” veterinarian Demian Dressler discusses something he says has been “kept under wraps, or hasn’t been spread in the veterinary community.” He cites statistics included in an article in Cancer Epidemiology Biomarkers and Prevention (Nov. 2002 11:1434–1440) to explain why Rotts may be vulnerable to osteosarcoma, an aggressive bone cancer common in large dogs: If a male Rott is neutered before one year of age, his risk of osteosarcoma almost quadruples. For a female Rott spayed before one year of age, the risk more than triples. (For other purebreds spayed or neutered before a year of age, the risk more than doubles.) So, those sterilized before their first birthdays had a roughly one-in-four lifetime risk for osteosarcoma and were far more likely than intact animals to develop a tumor. Dressler’s conclusion? “It’s my viewpoint that Rotts should be spayed and neutered after a year of age.”

 

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