Cancer remains a sobering fact of life: It will be the cause of death of more than one in five Americans. With the exception of tobacco- and occupation-related cancers, science does not know the precise origin of cancer, nor does it understand the exact mechanism involved in any cancer. It is not surprising that lack of knowledge about cancer has led to public and political confusion, contradiction, and misinformation. The Delaney Clause banning some food additives is one example. Despite the lack of evidence that the number of people getting cancer is increasing rapidly, the public and the press seem to believe that it is. In fact, if the incidence of lung and skin cancer, for which the major causes are known (tobacco and sun exposure), and breast cancer (which is likely related to hormone status) are not considered, cancer incidence and mortality would be flat or declining.
The central question in cancer prevention (as opposed to treatment) is "What strategy should we follow to prevent or reduce cancer?" Beginning in the 1950s and continuing through the 1970s, much of the scientific community believed that up to 90 percent of cancer was due to environmental causes, which was assumed to mean exposure to "chemicals." To most, this meant exposure to man-made chemicals that had been carelessly dispersed throughout the environment. This point of view was exemplified in Rachel Carson's Silent Spring, published in 1962. According to Carson, for the first time in recorded history humans were being exposed to dangerous levels of toxic substances from cradle to grave. We now know this to be untrue. For example, humans have always been exposed to potent carcinogens resulting from cooking protein-containing foods.
In the 1950s it appeared that a significant portion of cancer was caused by relatively few chemicals. There were only 50 or so known chemical carcinogens, most of which were synthetic. It was assumed that chemicals that produced cancer in animals would do so in humans. As this dogma became accepted, scientists and politicians formulated a three-pronged approach to cancer prevention. First, they established programs to determine which chemicals had the capacity to cause cancer. New institutions, such as the National Toxicology Program, the National Center for Toxicological Research, and the National Institute of Environmental Health Sciences, were given the task of determining which chemicals caused cancer. The second step was to find out where and how humans were exposed to these chemicals. It was assumed that any amount of exposure could lead to cancer; in theory even a single molecule represented a risk. Cancer-causing chemicals in our foods, water, and air could be detected at lower and lower concentrations. Detection limits went from parts-per-million in the 50s
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