Carcinogens

References to cancer have been found in the annals of human disease since ancient times, but the disease's association with carcinogen exposure is a relatively new concept. Sir Percival Potts, a British physician who lived in the eighteenth century, was the first to suggest that the induction of cancer might be linked to agents in the environment. Potts had observed high rates of scrotal and nasal cancer among England's chimney sweeps, men who were exposed to accumulated fireplace soot during their work. After some careful studies, Potts suggested correctly that exposure to soot caused the high cancer rates, providing the impetus for identifying other carcinogens present in the environment.

In retrospect, it was fortuitous that soot was acknowledged as one of the first carcinogenic agents. Soot is a complex mixture of chemicals that arises from the combustion of organic material. As scientists and physicians separated soot's individual components, it became clear that chemicals called polycyclic aromatic hydrocarbons (PAHs) were among its principal carcinogenic compounds. The story became even more intriguing when it was shown that many PAHs behave as procarcinogens. Procarcinogens do not cause cancer per se, but they can be converted to active carcinogens by enzymes located in organs like the liver and lung. The implications of this discovery are noteworthy. For example, cigarette smoke contains a wide variety of procarcinogenic PAHs that are turned into active carcinogens in lung cells. Since smokers draw these PAHs deep into their lungs with each inhale on a cigarette, one reason that cigarette smoking correlates so highly with the induction of lung cancer becomes very clear.