The Commoner Cancer Screen

Physicians smiled in disbelief a decade ago when Cancer Researcher Dr. John Higginson of the World Health Organization suggested that as many as 80% of all cancers were caused by agents in the environment. But no one is scoffing any more. The National Cancer Institute has published charts showing those areas of the country with the highest death rates from lung, liver and bladder cancer (see map); these areas also happen to have chemical plants--and chemical pollution. The obvious conclusion: Americans--and others elsewhere round the world--are increasingly filling their environment with chemicals that are not only harmful but may even be lethal.

Perfected Test. Medical scientists have been trying for decades to identify those chemicals that are carcinogenic. Their task is not easy. Throughout his evolution, man has been exposed to literally millions of chemical compounds; more recently, he has encountered synthetic compounds that did not even exist a generation or even a few years ago. Testing these compounds for ability to cause cancer currently requires extensive animal studies, which will take years and cost millions of dollars. But now there may be a way to speed up the search. In a report to the Environmental Protection Agency last week, Biologist Barry Commoner, who heads the Center for the Biology of Natural Systems at St. Louis' Washington University, announced that he had perfected a test that can not only identify possible carcinogens, but may also be able to pick out those individuals most likely to develop cancer as a result of exposure to them.

Commoner's work relies heavily upon a test devised by Dr. Bruce Ames of the University of California at Berkeley. Ames found that certain carcinogens were capable of causing mutations in bacteria. This suggested to Ames the possibility of using mutagenicity, the ability to cause mutations, which can be determined simply and quickly, as a test for carcinogenicity.

To determine the correlation, Commoner and his Washington University colleagues tested 92 chemical compounds on strains of the common bacteria Salmonella typhimurium, developed by Ames. Each compound was made up in three different concentrations and mixed with preparations made from seven different rat tissues (liver, kidney, brain, stomach, lung, spleen and blood); each of the mixtures was then added to culture dishes containing the Salmonella.

The results were dramatic. Of the 50 compounds that were known to be noncarcinogenic, only one, which happened to be a close chemical relative of a known carcinogen, caused the bacteria to mutate at a significant rate. Of the 42 other compounds, all known carcinogens, all but seven induced bacterial mutations by themselves. When the urine of rats that had been fed to three of the remaining compounds was placed in the culture dishes, it too produced mutations, suggesting that the chemicals, which may not cause cancer directly, are metabolized in the body into substances that do. With a slight change in the test method, three other compounds also proved mutagenic.

Commoner's test demonstrates that there is indeed a strong correlation between mutagenicity and carcinogenicity --at least in animals. "What we have needed," says Commoner, "is a fast way of looking at a chemical and telling if it is likely to cause cancer in some test animal. We would be satisfied with a method that made every presumptive carcinogen sit up and whistle Dixie. This test does the same thing by showing us that a chemical that is mutagenic is highly likely to be carcinogenic as well."

Cheap Way. The mutagenicity test, which can be done in 48 hours at a cost of about $500, gives doctors and environmentalists a quick, cheap way of determining whether a chemical compound is likely to be dangerous to animals. But Commoner's work is applicable to humans as well. It may enable researchers to tell whether an individual who has been exposed to a suspect substance is metabolizing it in such a way as to produce carcinogens. A doctor may soon be able to take a sample of his patient's urine and introduce it into a culture of Salmonella; if it causes mutations, the patient's system is probably modifying substances that may be carcinogenic. Such patients could then be monitored carefully in the hope that any cancers that might develop could be detected and treated early.

Mutagenic screening could also help prevent cancer, which will kill about 365,000 in the U.S. alone this year. It may be too late to help those who have already been exposed to chemical carcinogens, some of which may have been present in air, water, food and factories for decades.* But it is not too early to begin protecting the public against new compounds, which are being introduced at the rate of several hundred a year. Many substances, such as vinyl chloride and diethylstilbestrol (a hormone-like substance used to fatten cattle), were not recognized as having a cancer-causing potential until they had been in use for decades. Commoner's screen makes it possible to spot potential carcinogens before they get into the environment.

* "One example: the EPA last week took steps to ban most uses of the long-popular pesticides chlordane and heptachlor, which have been found to cause cancer in laboratory animals and are thus considered hazardous to humans as well.

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