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How and why do carcinogens cause cancer?


Determining a Substance's Link to Cancer

Imagine being on the team in charge of figuring out the known carcinogens around us. You wouldn't be able to wrap up your project all neat and tidy, filing it away marked complete. Instead, you would continue to research and refine your list, working on new revisions every couple of years. After all, your research would be linked to potentially preventing cancer, which is a matter of life and death.

In the last government report on carcinogens -- known as the "11th Report on Carcinogens (RoC)" -- 246 substances made it on the list. Of those substances, 58, such as alcoholic beverages, benzene, mustard gas and coal tars, were identified as known human carcinogens, while the other 188 were not as strongly labeled. Instead, they were referred to as "reasonably anticipated" to be substances linked to cancer [source: National Toxicology Program].

So just how does a substance make it on the list? Scientists rely on two different types of studies: lab and epidemiologic. In a laboratory environment, scientists are limited in what they can do, since they can't test on people. Therefore, they have to rely on cell cultures and animal testing. However, even that isn't enough because replicating exposures in people isn't possible, and it's impossible to say that a substance will act the same way in humans as it did in animals. Furthermore, to be able to use small sample groups, scientists must use doses markedly higher than human exposures when testing on animals. So scientists believe that positive carcinogen tests on animals are reasonable predictors of cancer risk and a justified reason to limit human exposure.

In contrast to laboratory studies, epidemiologic studies, also known as population-based studies, take research outside of the lab. In an epidemiologic study, researchers look at a population of people and target potential causes of cancer. The challenge here is that outside of the lab, scientists lose a controlled environment, meaning it's difficult to determine what someone is exposed to and when. Therefore, scientists aim to use the best of both worlds -- lab and epidemiologic studies -- to determine the carcinogens that are potentially life threatening.

And they're certainly life threatening, indeed. In fact, it's believed that 75 to 80 percent of cancer deaths in the United States are due to exposure to carcinogens rather than hereditary links to cancer [source: American Cancer Society]. However, that doesn't mean that we should all hide under a rock; there might be a carcinogen under that rock anyway. Instead, we can take a role in our own protection by limiting our contacts to known carcinogens. For example, staying away from tobacco, limiting alcohol consumption and avoiding too much sun exposure are all wise steps toward prevention. Just remember, keep your wits about you, and there are things you can do to stop some of those carcinogens in their tracks.


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