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Do Environmental Pollutants Cause Cancer in Dogs?

Other studies have shown that area of residence can increase the cancer risk. “The same study out of Italy showed that dogs that lived in the industrial areas had an 8.5 times higher risk of developing lymphoma than those living in urban areas,” says Moore. Similarly, a study published in 1971 in Archives of Environmental Health found that tonsillar squamous cell carcinoma was 10 times more common in animals living in cities than in those living in more rural environments. Both findings imply that urban living exposes animals to more environmental pollutants; however, they do not quantify an amount of urbanization or industrialization that significantly increases risk, or which anatomical characteristics put some individual dogs at greater risk than others. As Moore explains, other factors come into play, including long-nosed vs. short-nosed, or Scottish Terrier vs. other breeds, amount of exposure, and obesity.

The Biology of Cancer
This interplay of factors can in part be explained by the mechanism of cancer. Normally, cells have a set lifespan. They die and are replaced by new cells. During the cells’ lifespan, mutations in their DNA commonly occur, and though many are repaired, others are not, which often leads to early programmed cell death (apoptosis). Some mutations, however, result in prolonged cell survival, because mutations in the cell repair mechanisms or in the mechanisms that normally lead to programmed cell death have already taken place. In other words, these cells avoid apoptosis and divide in an uncontrolled manner. As they do so, they form an enlarging mass of cells that can invade local tissues as well as spread to other locations. Thus, cancerous cells are the result of multiple mutations occurring in the right combinations.

Because of these interactions, it can be difficult to appreciate some cancer risks. “Everyone knows about a 90-year-old guy who smoked all his life,” Moore says. “While smoking increases the risk of cancer, it may be that this person just doesn’t have the changes in his cells that can combine with the mutations caused by smoking to result in cancer.” More information is necessary. “It’s possible that the genome project will help identify genes related to getting cancer or being more at risk for getting cancer, but the risk may not present until the animal is exposed to the right environmental factors, such as herbicides, or becomes obese.”

Genes Play a Role
Clearly there are genetic factors. Says Glickman, “In the average breed, 20 to 30 percent of dogs die of cancer, but in other breeds, such as Golden Retrievers, it is probably 60 percent.” In some animals, the very traits that make them desirable as pets or especially skilled at certain tasks make them prone to certain cancers. For instance, Irish Wolfhounds and other large sighthounds bred for exceptional speed and ability to capture agile prey such as deer or rabbits are also prone to developing osteosarcoma (bone cancer). In fact, in general, dogs with legs longer than 50 cm (or a little less than 20 inches) are at risk for this cancer of the leg bones. Similarly, as noted earlier, the same trait that protects long-nosed dogs against lung cancer predisposes them to cigarette-related nasal cancers.

Information on genetic predispositions can be used to help decrease cancer risk. In the case of Scottish Terriers, Glickman is working with the National Cancer Institute to identify those at highest risk for bladder cancer and to establish the genetic basis for that predisposition. Says Glickman, “The goal is to screen all Scottish Terriers as puppies and identify those with higher risk of bladder cancer. Those that [have this risk] can have twice-yearly evaluations of urine to look for early signs, or can have an ultrasound performed every six months.” If the cancer is detected early on, it might be possible to remove it. But even more valuable is that with these predisposed dogs, exposure to lawn chemicals can be eliminated and diet can be changed. Consumption of vegetables—specifically leafy greens and yellow-orange vegetables—three or more times a week was associated with a 70 to 90 percent reduction in risk of developing transitional cell carcinomas in Scottish Terriers.

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Submitted by Dwight | January 31 2010 |

I'm a graduate of Ashland University with degrees in science and secondary education. One of my former professors, Dr. Weidenhamer, has made national news due to his research of childrens' toys and jewelry and presence of high levels of lead and cadmium contained within them. The biggest dangers occurs when the children have prolonged exposure to the lead and smaller children putting the toys in their mouth. Many of the toys that have shown extremely high levels of lead are ones made overseas (mostly China). Here's a link that about this: (http://personal.ashland.edu/~jweiden/lead.htm) and (http://blogs.consumerreports.org/safety/2009/09/lead-levels-in-childrens...).

My wife and I rescued a black lab mix dog. He goes through a lot of chew toys. While at the store, I noticed many of the toys we get for our dog also comes from overseas (ie. China). I've even come across some toys that are exactly the same as what's found at children's toy stores.

This got me to thinking. Should pet owners also be concerned of the possibility of lead in their pet toys? Has there been any research of the effects of lead in pets (dogs)? Since dogs tend to do a lot more of putting things in their mouth, chewing, and swallowing small amounts of chewed up plastic, what are the dangers of lead poisoning of our pets?

I've emailed my professor, Dr. Weidenhamer, regarding the testing of pet toys. He stated that some of the soft plastics used in pet toys are also used in physical therapy for people. Due to the large number of children's toys and general public's concern of their children, he doesn't have the time to test the pet toys.

We love our dog. He's an important part of our family. I know many others feel the same way about their dog(s). From going to the store the other day and seeing bottled water for dogs (which personally, I think is over the top), I know many people want the best for their dog...to be happy, healthy, loved, and well cared for. I feel that this is something that should also be looked into. Out of our love, I don't want to be an irresponsible pet owner and get something that could potentially be harmful for our dog. There are days that I believe our dog doesn't have too many IQ points to spare...he can't afford to lose anymore. (just kidding, he is pretty smart) Seriously, I think as a responsible pet owner, we need to speak on their behalf as to the hidden potential dangers of lead contained within pet toys.

So now, whenever we do get him some toys, I check the labels as to where they were made. It's not a guarantee, but hopefully it's a step in the right direction of keeping our beloved dog healthy.

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